US20080112885A1 - System and Method for Acoustic Data Transmission - Google Patents

Abstract

Embodiments of the present invention are directed to acoustic data transmission using a spreading code. A system for acoustic data transmission includes an ingestible capsule and an acoustic receiver. The ingestible capsule includes a modulator, a spreader, and an acoustic transmitter. The modulator modulates data according to a modulation scheme. The spreader spreads the modulated data according to a spreading code. The acoustic transmitter acoustically transmits the modulated and spread data through a body of an animal. The acoustic receiver includes an acoustic transducer a de-spreader and a demodulator. The acoustic transducer receives the acoustically transmitted signal and forms an electrical signal therefrom. The de-spreader de-spreads the received signal in accordance with the spreading code. The demodulator demodulates the received and de-spread signal in accordance with the modulation scheme, wherein a phase of the spreading code is synchronized with the received signal whereby a signal-to-noise ratio of the received signal is increased.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• The present application claims the benefit of U.S. Provisional Patent Appl. No. 60/842,360, filed Sep. 6, 2006, and U.S. Provisional Patent Appl. No. 60/941,184, filed May 31, 2007, each of which is incorporated by reference herein in its entirety.
BACKGROUND
• 1. Field of the Invention
• The present invention is generally directed to medical device communications, and in particular, to communication with an ingestible medical device.
• 2. Related Art
• An ingestible medical device may be used to diagnose and/or treat a patient. For example, the ingestible medical device may be used to collect data regarding the patient's internal body chemistry. This data can then be transmitted to an external device for diagnostic purposes. Such a diagnostic technique is easy to administer and less invasive compared to conventional diagnostic techniques, such as surgery.
• Conventional ingestible medical devices use a radio frequency (RF) signal platform to collect and transmit data to external devices. However, the RF signal platform is problematic for several reasons.
• First, the extent to which RF signals cause harm to human tissue is not fully understood. The potential for harm only increases as the source of the RF signals comes closer to the human tissue. Accordingly, patients may be apprehensive about ingesting a device that emits RF signals.
• Second, ingestible medical devices based on an RF signal platform consume a significant amount of power. To provide the requisite amount of power, RF-based ingestible medical devices include a relatively large power supply, making the overall size of such devices quite large. In fact, conventional RF-based ingestible medical devices are so large that they cannot be swallowed by a portion of the patient population. And, even if a patient can swallow a conventional RF-based ingestible medical device, its large size may cause it to become lodged in the patient's gastrointestinal tract, which would require surgery to remove.
• To circumvent problems associated with conventional RF-based ingestible medical devices, data from an ingestible medical device can be transmitted acoustically. An ingestible medical device that acoustically transmits data consumes less power than a conventional RF-based ingestible device, and can therefore be manufactured to be smaller than a conventional RF-based ingestible device. Also, low-power acoustic signals are not harmful to human tissue.
• Despite these and other advantages, acoustically transmitting data inside a human's body is problematic. The surface between the human's body and air is almost a perfect acoustic reflector. Consequently, the inside of the human's body is an acoustic reverberation chamber, in which sound echoes back and forth between internal surfaces until attenuation causes the sound to die out (i.e., fall below an amplitude sensitivity level). Even worse, this acoustic reverberation chamber is dynamic, with the echo characteristics changing over time. Many factors affect the dynamic behavior of this reverberation chamber, including breathing, the heart beat, speaking, organ movement, bowel function, vein pulsing, body movement, and even Doppler frequency shifting. As a result, an acoustic signal in the body will create a noise signal which is a complicated function of the multiple echoes of previously transmitted signals and which is amplitude modulated by the dynamic changes of the body cavity.
• This dynamic noise background significantly complicates acoustic data transmission within the body. During data transmission, multi-path propagation causes inter-symbol interference and signal fading in the time and frequency domains. Inter-symbol interference and signal fading (such as, Rayleigh fading) significantly decrease system performance, restrict data rate, dramatically increase power consumption, and sometimes even lead to complete transmission degradation.
• One possible method for mitigating the effects of the dynamic noise background is to merely wait until the noise from a first data bit or symbol dies out before sending another data bit or symbol. In this way, the subsequent data bit or symbol can be unambiguously identified by a receiving device. However, this method cannot be used to achieve high data rates. To achieve high data rates, data bits or symbols should be pushed through the channel in the presence of the dynamic noise.
• Therefore, what is needed is an improved ingestible medical device and a method for acoustically transmitting data from the same to achieve high data rates.
BRIEF SUMMARY
• The present invention meets the above-described need by providing systems and methods of acoustic data transmission which spread a data signal using a spreading code. The spreading code is quasi-orthogonal to reduce inter-symbol interference and improved system performance.
• An embodiment of the present invention provides a system for acoustic data transmission including an ingestible capsule and an acoustic receiver. The ingestible capsule includes a modulator, a spreader, and an acoustic transmitter. The modulator modulates data according to a modulation scheme. The spreader spreads the modulated data according to a spreading code. The acoustic transmitter acoustically transmits the modulated and spread data through a body of an animal. The acoustic receiver includes an acoustic transducer a de-spreader and a demodulator. The acoustic transducer receives the acoustically transmitted signal and forms an electrical signal therefrom. The de-spreader de-spreads the received signal in accordance with the spreading code. The demodulator demodulates the received and de-spread signal in accordance with the modulation scheme, wherein a phase of the spreading code is synchronized with the received signal whereby a signal-to-noise ratio of the received signal is increased.
• In embodiments, phase shift keying or differential phase shift keying is used in combination with a simple Barker spreading code, collectively providing substantial inter-symbol interference mitigation. In an embodiment, the Barker code is implemented as an 11-element cyclic shift register which conserves area and reduces power consumption, enabling an ingestible capsule of the present invention to be relatively small.
• Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. Note that the Summary and Abstract sections may set forth one or more, but not all exemplary embodiments of the present invention as contemplated by the inventor(s).
BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES
• The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention.
• FIG. 1 illustrates a partial view of a human according to an embodiment of the present invention.
• FIG. 2 is a block diagram of an ingestible capsule according to an embodiment of the present invention.
• FIG. 3 is a block diagram of a communications module according to an embodiment of the present invention.
• FIG. 4 is a block diagram of an ingestible capsule according to another embodiment of the present invention.
• FIG. 5 is a block diagram of a communications network according to an embodiment of the present invention.
• FIG. 6 is a block diagram of an exemplary communications network utilizing a sensor link module according to an embodiment of the present invention.
• FIG. 7 is a block diagram of a sensor link module according to an embodiment of the present invention.
• FIG. 8 is an exemplary computer system useful for implementing the present invention.
• FIG. 9 is a block diagram of an ingestible capsule according to yet another embodiment of the present invention.
• FIG. 10 is a circuit diagram of an acoustic communications module according to an embodiment of the present invention.
• FIG. 11 is a cross-section of a piezoelectric transducer according to an embodiment of the present invention.
• FIG. 12 is an exemplary step function.
• FIG. 13 is another exemplary step function.
• FIG. 14 is a block diagram of a phased array according to an embodiment of the present invention.
• FIG. 15 is an illustration of an acoustic biobus according to an embodiment of the present invention.
• FIG. 16 illustrates a power source for an acoustic transmitter according to an embodiment of the present invention.
• FIG. 17 illustrates a block diagram of an acoustic data transmission system utilizing a spreading code according to an embodiment of the present invention.
• FIG. 18 illustrates a block diagram of an acoustic transmitter that utilizes a phase shift keying (PSK) modulation scheme and a spreading code according to an embodiment of the present invention.
• FIG. 19 illustrates a block diagram of an acoustic receiver of an acoustic data transmission system that utilizes a PSK modulation scheme and a spreading code according to embodiments of the present invention.
• FIG. 20 illustrates a block diagram of a transmitter of an acoustic data transmission system that utilizes a differential PSK (DPSK) modulation scheme and a Barker spreading code according to an embodiment of the present invention.
• FIG. 21 illustrates a block diagram of a receiver of an acoustic data transmission system that utilizes a DPSK modulation scheme and a Barker spreading code according to an embodiment of the present invention.
• FIG. 22 illustrates a block diagram of a transmitter of an acoustic data transmission system that utilizes a DPSK modulation scheme and a Barker spreading code according to another embodiment of the present invention.
• FIG. 23 illustrates a block diagram of a receiver of an acoustic data transmission system that utilizes a DPSK modulation scheme and a Barker spreading code according to another embodiment of the present invention.
• FIG. 24 illustrates a block diagram of a receiver of an acoustic data transmission system that extracts a signal from a plurality of reflected signals according to an embodiment of the present invention.
• FIG. 25 illustrates a block diagram of a transmitter of an acoustic transmission system that uses two types of DPSK modulation according to an embodiment of the present invention.
• FIG. 26 illustrates a block diagram of a receiver of an acoustic transmission system that uses two types of DPSK modulation according to an embodiment of the present invention.
• FIG. 27 illustrates a frequency hopping (FH) scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 28 illustrates a hopping pattern used to encode and/or decode the acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 29A illustrates a combined FH and pulse interval encoding (PIE) scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 29B further illustrates the combined FH and PIE scheme according to an exemplary embodiment of the present invention.
• FIG. 30A illustrates a combined FH and differential phase shift keying (DPSK) scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 30B further illustrates the combined FH and DPSK scheme according to an exemplary embodiment of the present invention.
• FIG. 31 illustrates a block diagram of a transmitter to encode an information signal using a combined FH and DPSK scheme according to an exemplary embodiment of the present invention.
• FIG. 32 illustrates a block diagram of a receiver to decode an acoustic communication signal using a combined FH and DPSK scheme according to an exemplary embodiment of the present invention.
• FIG. 33A illustrates a hopping pattern used to encode and/or decode an acoustic communication signal using a combination of FH and differential frequency shift keying (DFSK) according to an exemplary embodiment of the present invention.
• FIG. 33B further illustrates the hopping pattern used to encode and/or decode the acoustic communication signal using the combination of FH and DFSK according to an exemplary embodiment of the present invention.
• FIG. 33C illustrates a combined FH and DFSK scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 34A illustrates a combined FH, DFSK, and DPSK scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 34B further illustrates the combined FH, DFSK, and DPSK scheme according to an exemplary embodiment of the present invention.
• FIG. 34C further illustrates the combined FH, DFSK, and DPSK scheme according to an exemplary embodiment of the present invention.
• FIG. 35 illustrates a block diagram of a transmitter to encode an information signal to a combination of FH, DFSK and DPSK acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 36 illustrates a block diagram of a receiver to decode an information signal from an acoustic communication signal encoded using a combination of FH, DFSK and DPSK according to an exemplary embodiment of the present invention.
• FIG. 37 illustrates a block diagram of a demodulator to decode an information signal from an acoustic communication signal encoded using a combination of FH, DFSK, and DPSK according to an exemplary embodiment of the present invention.
• FIG. 38 illustrates a block diagram of a demodulator to decode an information signal from an acoustic communication signal encoded using a combination of FH, DFSK, and DPSK according to another exemplary embodiment of the present invention.
• FIG. 39A illustrates a hopping pattern used to encode and/or decode an acoustic communication signal using multiple frequency bands with FH according to an exemplary embodiment of the present invention.
• FIG. 39B illustrates a multiple frequency band with FH scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 39C illustrates a multiple frequency band with FH and time interval encoding scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention.
• FIG. 39D illustrates an advancement function that may be used with the multiple frequency bands with FH and time interval encoding scheme according to an exemplary embodiment of the present invention.
• The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears.
DETAILED DESCRIPTIONI. Introduction
• Methods, systems, and apparatuses for ingestible capsules are described. Furthermore, methods, systems, and apparatuses for operating and communicating with the ingestible capsules are also described. The present specification discloses one or more embodiments that incorporate the features of the invention. The disclosed embodiment(s) merely exemplify the invention. The scope of the invention is not limited to the disclosed embodiment(s). The invention is defined by the claims appended hereto.
• References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
• Furthermore, it should be understood that spatial descriptions (e.g., “above,” “below,” “up,” “left,” “right,” “down,” “top,” “bottom,” “vertical,” “horizontal,” etc.) used herein are for purposes of illustration only, and that practical implementations of the structures described herein can be spatially arranged in any orientation or manner. Likewise, particular bit values of “0” or “1” (and representative voltage values) are used in illustrative examples provided herein to represent information for purposes of illustration only. Information described herein can be represented by either bit value (and by alternative voltage values), and embodiments described herein can be configured to operate on either bit value (and any representative voltage value), as would be understood by persons skilled in the relevant art(s).
• The example embodiments described herein are provided for illustrative purposes, and are not limiting. Further structural and operational embodiments, including modifications/alterations, will become apparent to persons skilled in the relevant art(s) from the teachings herein.
• Methods and systems for an ingestible capsule are described. The ingestible capsule may be swallowed by an animal to diagnose or aid in the diagnosis of one or more conditions of the animal through either an immediate detection or a historical and/or statistical analysis of multiple detections of conditions or attributes over a time period. Example embodiments are described below as related to a human subject, for illustrative purposes. However, embodiments of the present invention are applicable to further types of animals other than humans, including livestock (cattle, sheep, pigs, chickens, turkeys, ostriches, etc.), pets (e.g., dogs, cats, horses, etc.), and other animals of interest such as race horses or other performance/sport animals. Such applicability to these types of animals, and other types, will be apparent to persons skilled in the relevant art(s) from the teachings herein, and is within the scope and spirit of embodiments of the present invention.
• Furthermore, example embodiments are described below as related to passing an ingestible capsule through a gastrointestinal tract, for illustrative purposes. However, embodiments of the present invention are applicable to further bodily systems other than the gastrointestinal tract, including the circulatory system, the urinary tract, and other bodily systems and additionally other means of entry or implant into a body cavity of an animal or human. Such applicability to other types of bodily systems will be apparent to persons skilled in the relevant art(s) from the teachings herein, and is within the scope and spirit of embodiments of the present invention.
II. Ingestible Acoustic Device
• FIG. 1 shows a partial view of a human102 according to an embodiment of the present invention. InFIG. 1, human102 has swallowed or ingested aningestible capsule104.Ingestible capsule104 is configured to sense one or more attributes or conditions of human102 asingestible capsule104 passes throughhuman102. While passing throughhuman102,ingestible capsule104 transmits information in acommunication signal106 to be received on the outside of the human102.Ingestible capsule104 may send information to and receive information from an external device, or it may be a beacon that only emits information to the external device. As shown inFIG. 1, anexternal computing device108 may receivecommunication signal106.Computing device108 may be used to display the information received incommunication signal106, to interact with the information, to process the information, and/or to transmit the information (raw or processed) to another entity or component. In an embodiment,computing device108 can interact withingestible capsule104 to control functions ofingestible capsule104.
• In a simplistic embodiment,computing device108 may simply act as a protocol converter in a store and forward manner. However, in a more complex environment,computing device108 may perform complex and intensive functions such as data normalization, compression, and encryption for example.
• In another advanced embodiment,computing device108 can interact withingestible sensor device104 to control functions ofingestible sensor device104. This embodiment infers abi-directional communication106 withsensor device104. Bi-directional communications are generally common place with persons skilled in the art. However, these designs are typically designed to be able to receive signals either at times not transmitting, or at all times. These common techniques are not desirable in the described environment as receivers require power, and additional power would consequently add to the size ofsensor device104.External computing device108 receives and stores commands and/or information from a network. Upon termination of the next transmission fromsensor device104,sensor device104 may turn on a receiver for a very short amount of time, whileexternal device108 commences transmission of commands or information tosensor device104. Greatly reduced power requirements onsensor device104 are gained from very rapidly turning off a receiver when no communications (or an indication of no information to communicate) are received fromdevice108 within a defined time window after a last transmission fromsensor device104.
• In embodiments, human102 may be provided with one or moreingestible capsules104 that human102 may at designated times and/or periodically swallow to perform an analysis of one or more health-related conditions ofhuman102. Multipleingestible capsules104 may interact withdevice108 and/or each other. An exemplary ingestible capsule is described in co-pending U.S. patent application Ser. No. ______, Attorney Docket No. 2520.0020001, titled “Ingestible Low Power Sensor Device and System for Communicating with Same,” which is incorporated by reference herein in its entirety.
• FIG. 2 shows an example block diagram ofingestible capsule104, according to an embodiment of the present invention. InFIG. 2,ingestible capsule104 includes an acousticallytransmissive encapsulation208 that holds one or more sensors202, acommunications module204, and apower source206. AlthoughFIG. 2 illustratesingestible capsule104 as having threesensors202a,202b, and202c, one of skill in the art will recognize that any number of sensors may be included iningestible capsule104. In one embodiment, there may be no sensor(s)202 at all, providing a capability to track the pill movement in space, hence allowing a mapping of a gastro-intestinal tract and also the time of movement within that tract.
• In an embodiment whereingestible capsule104 has one or more sensor(s)202, sensor(s)202 are used to sense (e.g., measure, detect, etc.) a receivedstimulus210, and generate asensor output signal212.Sensor output signal212 may be a digital or analog signal, depending on the particular implementation of sensor202. In alternative embodiments the acousticallytransmissive encapsulation208 may be made of sensor(s)202, or sensor202 may be integrated within the materials known as acousticallytransmissive encapsulation208.Ingestible capsule104 can include any number of sensors202, each of which may all sense the same condition or may sense a different condition than another sensor202. Sensor202 may detect and/or interact directly with conditions of the body. Sensor202 may also detect and/or interact with signals emanating from the pill and reflecting off nearby tissues, such as is the case with, for example and without limitation, a camera detecting light that originates from the capsule, ultrasonic detectors, and radioactivity sensors. In an embodiment, sensor202 detects reflections ofsignal106 from nearby gastro-intestinal and other body tissues.
• Logic control214 initiates activity of sensor202. Sensor202 detects or interacts with the body viasignal210 and produces asensor output signal212.Communications module204 receivessensor output signal212, and generatescommunication signal106 to include information based onsensor output signal212.Communication signal106 is transmitted fromingestible capsule104.
• In an example embodiment, as shown inFIG. 3,communications module204 may include anacoustic communications module302, configured to transmit and/or receive an acoustic communications signal. For example,acoustic communications module302 may include one or more acoustic transducers.Sensor output signal212 is modulated on an acoustic signal that is transmitted as communications signal106 by the acoustic transducer(s). The acoustic communications signal106 may be transmitted by radiatingelement304, which may be, for example, an electromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.) element or transducer that vibrates at acoustic or ultrasonic frequencies. An example acoustic frequency range in whichacoustic communication signal106 may be transmitted is 20 Hz to 16 KHz, although the frequency may be an acoustic frequency higher or lower than this range in some applications. An example frequency for acoustic communications signal106 is 40 Hz. In another example embodiment,acoustic communications module302 may include an ultrasonic communications module, configured to transmit and/or receive a communications signal at ultrasonic frequencies (e.g., between 0.5 to 5 MHz). Generally, transducers are smaller for ultrasonic frequencies, which is useful for a very small sensor device. However, smaller devices also generally transmit less power through a medium and thus need to have a high power input and hence a larger battery. Higher frequency transducers do generally have a higher bandwidth and may have an impact on the amount of sensor data can be transmitted to a receiver. However, attenuation is greater for higher frequencies. A person skilled in the art of acoustic transducers will be able to select an appropriate frequency range for an ideal situation of size and power consumption.
• Communications module204 may be configured to modulate information ofsensor output signal212 according to a variety of modulation techniques, including amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM), and including any combination of these modulation techniques, including in quadrature or other modulation schemes. Acoustic pressures according to embodiments may have various levels, including greater or lower than 1 Pa, including in the KPa (or greater) range to the μPa (or less) range.
• FIG. 4 shows a view ofingestible capsule104, withcommunications module204 includingacoustic communications module302. InFIG. 4,communications module204 is coupled to acousticallytransmissive encapsulation208.Acoustically transmissive encapsulation208 vibrates according toacoustic communications module302 to transmit acommunications signal402, which is an acoustic version of communications signal106. InFIG. 4, acousticallytransmissive encapsulation208 functions as an acoustic radiating element, vibrating at acoustic frequencies according toacoustic communications module302.
• Returning toFIG. 2, operation ofingestible capsule104 may be gated and controlled bycontrol logic214, which itself may be operating in a sub-threshold voltage (Vt) manner (e.g., to save power), orcontrol logic214 may operate in normal bias modes. In an embodiment,ingestible capsule104 is an autonomous device with one way communication (transmission capability), so thatcontrol logic214 may be extremely simple, and thus would not consume much power even when operating in normal bias modes. However, in another embodiment,ingestible capsule104 may communicate in both directions, and may be configured to receive instructions fromcomputing device108.Control logic214 may thus have additional complexity in order to, for example, decode and implement received instructions.
• Power source206 provides power (e.g., via electrical energy) to operate the components ofingestible capsule104 that require power, such ascommunications module204 and/or sensor202.Power source206 may include, for example and without limitation, a battery, a liquid, or an energy harvesting module.
• In an embodiment,power source206 includes a liquid or semi-liquid, such as is illustrated inFIG. 16. In this embodiment, communications signal106 is a signal of acoustic nature, andpower source206 includes anelectrolyte1601 in the form of an acoustically transmissive material such as a liquid or semi-liquid.Electrolyte1601 serves a first purpose of a battery component but also serves an efficient medium of acoustic transmission. Furthermore, as illustrated inFIG. 16, amaterial1602 serves a dual purpose ofhousing battery1601 as well as other components, while allowing an efficient transfer of acoustic energy from inside to outside ofingestible capsule104.FIG. 16 additionally demonstrates control andregulation component206a,anode206b, andcathode206c.
• Communication signals106 pass throughelectrolyte1601 and externalanimal flesh environment1603. In the case of an acoustic propagation, the most efficient energy transfer is accomplished when the acoustic material impedance from material to material is gradually changed from origin to destination from high to low, or low to high impedance as is common knowledge to those skilled in the art.Communication signal106 then is demonstrated inFIG. 16 as a combination ofsignals106aand106bto illustrate the change in medium properties fromelectrolyte1601 throughhousing material1602 and intoflesh1603. As one example of many,electrolyte1601 may be a citric juice or gel that is non-harmful to human consumption;anode206bandcathode206cmay include zinc and copper, which is also not harmful to human consumption; andhousing1602 may be comprised of a thin but soft plastic of reasonable acoustic impedance toelectrolyte1601 andanimal flesh1603. However, other material selections by those skilled in the art of battery technology and acoustic propagation forelectrolyte1601,housing1602,anode206bandcathode206cdo not depart from the spirit of this invention.
• In an embodiment,ingestible capsule104 is configured for low power operation, including extreme low power (XLP) operation. To achieve XLP operation,ingestible capsule104 can use one or both of a very small battery and energy harvesting to operateingestible capsule104. In an embodiment, circuits ofingestible capsule104 are implemented in one or more integrated circuits (ICs), in a technology such as CMOS, or other technology. The IC(s) and any other internal components ofingestible capsule104 may be mounted to a circuit board, or mounted directly to acousticallytransmissive encapsulation208. Thus, in embodiments,power source206 is configured for low power output, including supplying power in the milliwatt and microwatt ranges. Such low power requirements enable the size ofpower source206 to be minimal.
• In a CMOS embodiment, MOSFET circuits may be configured to operate in a deep sub-threshold voltage (sub-Vt) mode, which lowers their switching time to acoustic switching frequencies, and lowers their power consumption by orders of magnitude. In such a mode the MOSFET devices operate as analog devices. Such operation was demonstrated in the mid-1980's by Carver Meade with regard to eye and ear chips. Such a mode of operation eliminates the need for digitizing the sensor information, which can be very power intensive, and which further reduces the power consumption by a large factor. Further details on such sub-threshold voltage MOSFET circuits may be found in the following U.S. patents, which are incorporated herein by reference in their entirety: U.S. Pat. Nos. 6,198,324, 6,252,448, 6,297,668, and 6,333,656.
• Acoustically transmissive encapsulation208 contains sensor202,communications module204, andpower source206, and is configured to be ingestible by or inserted within a human and/or animal.Acoustically transmissive encapsulation208 may be the size of a vitamin or other type of pill that is ingestible by humans. For example, acousticallytransmissive encapsulation208 may be approximately 3 mm in diameter and approximately 5 mm in length.Acoustically transmissive encapsulation208 may be any suitable shape, including oval, elliptical (as shown inFIG. 2), capsule shaped, or spherical. The small size of acousticallytransmissive encapsulation208 allowsingestible capsule104 to be easily ingested by anaverage human102. The small size overcomes difficulties present with existing camera pills, which are often so large that only a small percentage of the population can actually swallow them. Further, the small size of acousticallytransmissive encapsulation208 increases the ability ofingestible capsule104 to pass completely through the digestive system of a human102 without becoming trapped due to size incompatibility.
• Acoustically transmissive encapsulation208 may be made from a variety of non-digestible or slow rate of digestion materials, including: a plastic material, such as a resin, a resinoid, a polymer, a cellulose derivative, a casein material, and/or a protein; a metal, including a combination of metals/alloy; a glass material; a ceramic; a composite material; and/or other material/combination of materials. In a particular embodiment, acousticallytransmissive encapsulation208 may be comprised of a material that aids in the sensing of biological, chemical, or other attributes of body material that touches or comes in close proximity to the acousticallytransmissive encapsulation208, such as could be called an integrated encapsulation and sensor material.
• After being swallowed byhuman102,ingestible capsule104 eventually passes fromhuman102, such as when human102 has a bowel movement to excrete waste. In an embodiment,ingestible capsule104 is disposable. In another embodiment,ingestible capsule104 may be recovered, (and recycled) for reuse.
• Depending upon the ability or control of the patient,ingestible capsule104 may alternatively be inserted into a lower gastrointestinal tract of human102 as a suppository device.
• Depending on the configuration of sensor202, while passing throughhuman102,ingestible capsule104 can sense conditions and/or features of any part of the gastrointestinal tract, and any of the materials/fluids contained within and/or secreted by the organs in the gastrointestinal tract or organs indirectly associated with the gastrointestinal tract.Ingestible capsule104 can also receive conditions or signals from even more remote body organs such as acoustic pickup of heartbeat and/or breathing and more indirect conditions such as temperature. In an embodiment, a camera is coupled toingestible capsule104 to allow visual observation ofhuman102.
• As mentioned,ingestible capsule104 transmits information incommunication signal106 to be received outsidehuman102, such as by computingdevice108. In an embodiment,computing device108 may be configured to communicate with aremote entity502, such as shown in an examplesensor communications network500 shown inFIG. 5.Computing device108 may be configured to communicate withremote entity502 using wired and/or wireless links, in a direct fashion or through anetwork504. For example,computing device108 transmits acommunication signal506 tonetwork504, which transmits acommunication signal508 toremote entity502.Network504 may be any type of network or combination of networks, such as a telephone network (e.g., a land line and/or cellular network), a personal area network (PAN), a local area network (LAN), and/or a wide area network (WAN) such as the Internet.
• Remote entity502 may be one or more of a variety of entities, including a human and/or computer-based entity. For example,remote entity502 may include a doctor who receives information collected by ingestible capsule104 (and optionally processed by computer device108) incommunication signal508.
• As shown inFIG. 5,sensor communications network500 may include a return communications path fromremote entity502 throughnetwork504 tocomputing device108. For example, areturn communication signal510 is transmitted byremote entity502 tonetwork504, which transmits areturn communication signal512 tocomputing device108. In this manner, remote entity502 (e.g., doctor and/or computer system) can provide feedback tocomputing device108 incommunication signal512 regarding the analysis of human102 performed byingestible capsule104.Return communication signal512 may include any type of data/information format for providing the feedback, including an email, a text message, a text file, a document formatted for commercially available word processing software, a proprietary document/data format, auditory alarms, alerts and messages, etc.
• Ingestible capsule104 may also communicate withcomputing device108 via an intermediatesensor link module602, as shown inFIG. 6.Sensor link module602 receivescommunication signal106 fromingestible capsule104.Sensor link module602 transmits acommunication signal604 tocomputing device108, to provide the information sensed by sensor202 tocomputing device108. For example,sensor link module602 may be used wheningestible capsule104 communicates using an acoustic communications signal having a power level too low to reliably be received by computingdevice108. As shown inFIG. 6,sensor link module602 is coupled tohuman102.
• In another embodiment,sensor link module602 may provide a communication interface betweeningestible capsule104 andnetwork504, such that aseparate computing device108 is not required. In such an embodiment,sensor link module602 may perform some or all functions ofcomputing device108 described above, and thussensor link module602 may be referred to as a computing device.
• Multiplesensor link modules602 may provide a capability of location detection through triangulation and other algorithms, capable of detectingsensor device104 to a very accurate, three (3) dimensional location withinhuman102. In an embodiment, multiplesensor link modules602 may be attached to human102 at various locations in order to receive the interior acoustic signal from different positions.Sensor link module602 may be, for example, directly attached to the skin ofhuman102, such as by an adhesive or a strap.Sensor link module602 may be attached to human102 in one or more locations, including the head, neck, chest, back, abdomen, arm, leg, etc. With regard to receivingcommunication signal106 fromingestible capsule104 passing through the gastrointestinal tract,ingestible capsule104 may be attached to the neck, chest, back, and/or abdomen for a short signal path.
• An amount of received information is in part proportional to the number ofsensor link modules602 attached tohuman102. The array ofsensor link modules602 may be attached at specific locations on human102 to increase, and even maximize, the received diagnostic information. Multiplesensor link modules602 can identify a specific location of theingestible capsule104 which can be used for linking a location to the detection of a sensed material. The location can also be used to identify a historical analysis of the track taken by the ingestible capsule and the speed of passage.
• For example, the attachment of an array of three or moresensor link modules602 to human102 may enable triangulation or other location finding algorithms to be used to locateingestible capsule104 inhuman102. Alternatively, one or moresensor link modules602 having three or more receivers each may be used to the same effect. Further details regarding location of an ingestible capsule may be found in co-pending U.S. patent application Ser. No. ______, Attorney Docket No. 2520.0120001, titled “Imaging and Locating Systems and Methods for a Swallowable Sensor Device,” incorporated by reference herein in its entirety. By locatingingestible capsule104 inhuman102, a location of a sensed material inhuman102 can be determined.
• In embodiments,sensor link module602 may be configured in various ways. For instance,FIG. 7 shows an examplesensor link module602, according to an embodiment of the present invention. As shown inFIG. 7,sensor link module602 includes acontrol logic702, asensor communication module704, astorage706, aremote communication module708, and apower source710.
• Sensor communication module704 receivescommunication signal106 fromingestible capsule104.Sensor communication module704 demodulates the sensor-related information ofcommunication signal106. Furthermore,sensor communication module704 may process and/or convert a format of the information received incommunication signal106. For example,sensor communication module704 may perform an analog-to-digital (A/D) conversion of the received sensor information, and outputs a sensor information signal. The sensor information signal may be received bystorage706 and/or bycontrol logic702. In an embodiment,sensor link module602 may convert a communications signal106 (for example, an acoustic protocol) into an industry adopted or standardized communications signal604 (for example, Medical Implant Communications Services (MICS), an RF medical devices standardized protocol). Such an embodiment may not requiremuch storage706, potentially as small as a single register device.
• In other embodiments,storage706 is configured to store the sensor information of the sensor information signal.Storage706 may include any type of suitable storage, including a hard drive and/or memory devices. For example, in an embodiment,storage706 includes a read/write non-volatile memory, such as a secure digital (SD) memory card as is typically used in a PDAs and digital cameras.Storage706 can output the stored information in a stored sensor information signal, for subsequent transmission tocomputing device108 byremote communication module708. In an embodiment with a removable storage706 (SD memory, for example), physical removal of the memory and insertion intocomputing device108 orremote entity404 may be both possible and cost effective.
• Control logic702 is configured to control operation ofsensor link module602.
• Remote communication module708 receives the stored sensor information signal, and formats the sensor-related information for transmission. Furthermore,remote communication module708 transmits the sensor information incommunication signal604.Remote communication module708 may be configured to transmitcommunication signal604 in a variety of formats/protocols, such as a standard RF communication protocol including Bluetooth, IEEE 802.11, Zigbee, or other communication protocol, standard or otherwise. For example, in embodiments,computing device108 may be a Bluetooth, 802.11, and/or Zigbee configured handheld device such as cell phone, personal digital assistant (PDA), a Blackberry™, wrist watch, music player, or laptop, or other type of computer, handheld, desktop, or otherwise.Remote communication module708 may also transmit an identification number assigned toingestible capsule104 for identification by a receiver.
• Power source710 provides power to elements ofsensor link module602 that require power, such ascontrol logic702,sensor communication module704,storage706, andremote communication module708. For example,power source710 may include one or more batteries that are rechargeable ornon-rechargeable. Power source710 may also (or alternatively) include an interface for externally supplied power, such as standard AC power.
• As described above, in an embodiment,ingestible capsule104 can transmit an acoustic signal. By receiving the acoustic signal transmitted byingestible capsule104,sensor link module602 may perform a type of ultrasound analysis based on the human interior generated acoustic signal fromingestible capsule104. Asacoustic communication signal106 is transmitted through human102 fromingestible capsule104, signal106 is transformed by attenuation, refraction, and reflection, as a function of the tissue of human102 that signal106 passes through. The transformed signal thus provides additional diagnostic information tosensor link module602, very much like a diagnostic ultrasound conveys diagnostic information that can be analyzed by a trained technician. The acoustic signal fromingestible capsule104 may be viewed as an “interior” ultrasound or “sonogram”, which can be analyzed to extract additional diagnosticinformation regarding human102. In an embodiment, information received bysensor link module602 regarding the interior ultrasound signal can be used to generate a graphical display of at least a portion of the interior ofhuman102.
III. Example Computer System Embodiments
• According to an example embodiment, an ingestible capsule may execute computer-readable instructions to perform its functions. Furthermore, a sensor link module for communicating with the ingestible capsule may execute computer-readable instructions to communicate with the ingestible capsule. Still further, a computing device may execute computer-readable instructions to communicate with the ingestible capsule and/or the sensor link module, and/or to process information obtained by the ingestible capsule and/or sensor link module, as described above. Still further, a test kit and medical diagnostic network system may each execute computer-readable instructions to perform its functions.
• In one embodiment, one or more computer systems are capable of carrying out the functionality described herein. An example of acomputer system800 is shown inFIG. 8.
• Thecomputer system800 includes one or more processors, such asprocessor804. Theprocessor804 is connected to a communication infrastructure806 (e.g., a communications bus, cross-over bar, or network). Various software embodiments are described in terms of this exemplary computer system. After reading this description, it will become apparent to a person skilled in the relevant art(s) how to implement the invention using other computer systems and/or architectures.
• Computer system800 can include adisplay interface802 that forwards graphics, text, and other information from the communication infrastructure806 (or from a frame buffer not shown) for display on thedisplay unit830.
• Computer system800 also includes amain memory808, preferably random access memory (RAM), and may also include asecondary memory810. Thesecondary memory810 may include, for example, ahard disk drive812 and/or aremovable storage drive814, representing a floppy disk drive, a magnetic tape drive, an optical disk drive, etc. Theremovable storage drive814 reads from and/or writes to aremovable storage unit818 in a well known manner.Removable storage unit818 represents a floppy disk, magnetic tape, optical disk, etc. which is read by and written to byremovable storage drive814. As will be appreciated, theremovable storage unit818 includes a computer usable storage medium having stored therein computer software and/or data.
• In alternative embodiments,secondary memory810 may include other similar devices for allowing computer programs or other instructions to be loaded intocomputer system800. Such devices may include, for example, aremovable storage unit822 and aninterface820. Examples of such may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an erasable programmable read only memory (EPROM), or programmable read only memory (PROM)) and associated socket, and otherremovable storage units822 andinterfaces820, which allow software and data to be transferred from theremovable storage unit822 tocomputer system800.
• Computer system800 may also include acommunications interface824. Communications interface824 allows software and data to be transferred betweencomputer system800 and external devices. Examples ofcommunications interface824 may include a modem, a network interface (such as an Ethernet card), a communications port, a Personal Computer Memory Card International Association (PCMCIA) slot and card, etc. Software and data transferred viacommunications interface824 are in the form ofsignals828 which may be electronic, electromagnetic, optical or other signals capable of being received bycommunications interface824. Thesesignals828 are provided tocommunications interface824 via a communications path (e.g., channel)826. Thischannel826 carriessignals828 and may be implemented using wire or cable, fiber optics, a telephone line, a cellular link, a radio frequency (RF) link and other communications channels.
• In this document, the terms “computer program medium” and “computer usable medium” are used to generally refer to media such asremovable storage drive814 and a hard disk installed inhard disk drive812. These computer program products provide software tocomputer system800. The invention is directed to such computer program products.
• Computer programs (also referred to as computer control logic) are stored inmain memory808 and/orsecondary memory810. Computer programs may also be received viacommunications interface824. Such computer programs, when executed, enable thecomputer system800 to perform the features of the present invention, as discussed herein. In particular, the computer programs, when executed, enable theprocessor804 to perform the features of the present invention. Accordingly, such computer programs represent controllers of thecomputer system800.
• In an embodiment where the invention is implemented using software, the software may be stored in a computer program product and loaded intocomputer system800 usingremovable storage drive814,hard drive812 orcommunications interface824. The control logic (software), when executed by theprocessor804, causes theprocessor804 to perform the functions of the invention as described herein.
• In another embodiment, the invention is implemented primarily in hardware using, for example, hardware components such as application specific integrated circuits (ASICs). Implementation of the hardware state machine so as to perform the functions described herein will be apparent to persons skilled in the relevant art(s).
• In yet another embodiment, the invention is implemented using a combination of both hardware and software.
IV. Acoustic Information Exchange
• Because signals are transmitted betweeningestible capsule104 and an external receiver and/or transmitter, the signals necessarily pass through living tissue ofhuman102. To minimize damage to the tissue,ingestible capsule104 is configured for low power operation, including extreme low power (XLP) operation. Operating at a lower power than existing camera pills or radio frequency (RF) based pills enablesingestible capsule104 to have a smaller, longer-lasting battery than existing pills. Low power operation also provides the flexibility to allocate power to functions ofingestible capsule104 other than information exchange without sacrificing size. For example, reducing the power for information exchange enables additional power to be used to drive multiple sensors.
• Ingestible capsule104 can achieve low power communications by using acoustic signals for information exchange. The acoustic channel can deliver reliable information (e.g., a signal having a signal-to-noise ratio of approximately 15 dB) with a total required transmission power as low as a few microwatts, depending on the amount of information that is transmitted. Such low power is a possibility becauseingestible capsule104 need not transmit the signal any farther than approximately 20 cm (e.g., from the innermost point in human102 to a detector on the skin of human102).
• As discussed with respect toFIG. 3,ingestible capsule104 may include an acoustic communications module, such asacoustic communications module302, configured to transmit and/or receive an acoustic communications signal. For the acoustic transmitter to effectively transmit a signal for detection outside the body, the signal must have a relatively high signal-to-noise ratio (SNR), such as, for example, 15 dB. Methods and systems for increasing the SNR will be described further below. Additionally, since the pill may rotate or otherwise change orientation while insidehuman102, the acoustic signal should be transmitted substantially omnidirectionally.
• In an embodiment, omnidirectionality can be obtained by creation of a spherical transducer that launches a spherical wave front. In another embodiment, omnidirectionality may be implemented with multiple transducers having a more directional radiation pattern utilized in sequential time periods transmitting the same information on multiple transducers. Orientation of these transducers is most efficient when the orientations of the peak signal are orthogonally placed within a final configuration. The number of transducers, the amount of information sent in a time period, and the algorithm employed to switch to another time period and transducer may be determined by a person having skill in the art without departing from the spirit and scope of the present invention.
• As previously described,FIG. 4 shows a spherical embodiment ofingestible capsule104, whereinsignal106 is transmitted omnidirectionally via a single acoustic transducer. When signal106 is transmitted from the single acoustic transducer, signal106 interacts with various surfaces, for example, the internal tissue and skin ofhuman102. Interaction with these surfaces results in one or both of reinforcement reflections and cancelling reflections that may interfere withsignal106. As a result, some of the information carried insignal106 may be corrupted by the time it reaches an external receiver. Further, if the receiver is located at a null in the signal, no information will be received at all. In an embodiment, multiple external receivers may be utilized. Reflections (constructive or destructive) may interfere withsignal106, resulting in different signals being received by each of the multiple external receivers. Such an embodiment allows signal106 to be received from one external receiver even whensignal106 is too distorted to be correctly detected on an external receiver.
• FIG. 9 illustrates an alternative embodiment of aningestible capsule104 that reduces problems with interfering signals.Ingestible capsule104 is capsule-shaped, and includes two acoustic transducers,904aand904b. In an embodiment,acoustic transducers904aand904bare each placed at an equal distance from their respective ends.Transducer904atransmits anoutput signal106a.Transducer904btransmits anoutput signal106b. Due to the placement oftransducers904aand904bnear the ends of ingestible capsule902, the combined effect ofoutput signals106aand106bis an output signal having a uniformity similar to that of an omnidirectional transmitter. Furthermore, iftransducers904aand904bare appropriately spaced, nulls in the output signal can be eliminated. For example, if the spacing betweentransducers904aand904bis approximately one-half the wavelength of the transmitted signal, a signal produced by one transducer will be received even when the signal produced by the other transducer is at a null.
• In another embodiment,transducers904aand904bneed not be located with specific spacing or orientation referenced to a frequency of operation as depicted inFIG. 9. In this embodiment, information can be transmitted during a first time period ontransducer904a, providingsignal106ato be received by one or multiple external receivers. Subsequently, a duplicate set of information may be transmitted during a second time period ontransducer904b, providingsignal106bto be received by one or multiple external receivers. By having different origins ofsignals106, but the same content, an external receiver is likely to properly receive asignal106bin the event that signal106ahas been severely impacted by destructive interference caused by reflections of the signals off a variety of body parts and cavities. WhileFIG. 9 depicts use of two transducers, the use of three or more transducers gains more probability that signals are received and do not depart from the scope and spirit of this invention.
• FIG. 10 shows an example circuit1000 foracoustic communications module402, according to an embodiment of the present invention. As shown inFIG. 10, circuit1000 includes anoscillator1002, anamplifier1004, and anacoustic transducer1006. In the example ofFIG. 10,sensor1012 has a resistance (or other impedance value) that changes based on the sensed stimulus,stimulus1010. For example,sensor1012 may be a temperature sensor.Sensor1012 is coupled in series withoscillator1002, which may be a current-dependent oscillator configured to operate in a deep-threshold voltage (Vt) range to lower an oscillation frequency generated byoscillator1002 to a desired acoustic frequency range. As the resistance ofsensor1012 changes, the oscillator frequency changes in a predictable way. An output ofoscillator1002 is coupled to an input of anamplifier circuit1004 for amplification. An output ofamplifier1004 is input to acoustic transducer1006 (which may include or be coupled to an acoustic radiating element or acoustic actuator) that acts as a “speaker” to send the acoustic information out in anacoustic communication signal106.Acoustic transducer1006 may be, for example, one or more piezoelectric transducers. Althoughacoustic transducer1006 is described as being used for transmitting a signal, one of skill in the art will recognize thatacoustic transducer1006 may also be used to receive an incoming acoustic signal. Additionally, although circuit1000 is discussed herein as transmitting sensor information, one of skill in the art will recognize that circuit1000 may also be modified to receive information fromtransducer1006. Further, although circuit1000 is discussed herein as transmitting sensor information, one of skill in the art will recognize that circuit1000 may also be used to transmit acoustic signals used for imaging and/or locationing without departing from the spirit and scope of the present invention.
• In another embodiment, no oscillator is needed to drive oscillation ofacoustic transmitter1006. Instead, an electromechanical modulation method using only a DC voltage instead of an internal oscillator may be used to modulate information intooutput signal106. The electromechanical modulation method takes advantage of the nature of piezoelectric elements to expand or contract in response to an applied voltage. If voltage is applied in an appropriate manner, the resulting expansion or contraction of the piezoelectric element can be indicative of “1” and “0” bits in an information stream.
• FIG. 11 is a block diagram illustrating a cross-section of an exemplarypiezoelectric transducer1102 for modulating information intooutput signal106 using electromechanical modulation. InFIG. 11, a voltage V is coupled acrosspiezoelectric transducer1102. When voltage V is equal to 0 V,piezoelectric transducer1102 is uncompressed and has a given acoustic impedance. When voltage V is greater than 0,piezoelectric transducer1102 is compressed (e.g., clamped), which increases the spring force. This compression makespiezoelectric transducer1102 stiffer, changing the acoustic impedance ofpiezoelectric transducer1102.Piezoelectric transducer1102 thus has a first resonant frequency at 0 V and a second resonant frequency at the higher voltage.
• A step function may be applied topiezoelectric transducer1102 to take advantage of the resonant frequency variation.FIG. 12 illustrates anexemplary step function1202. Atpoint1204, the voltage acrosspiezoelectric transducer1102 is suddenly increased from, for example, 0 V to 10 V. Although this example will be described with using a low voltage of 0 V and a high voltage of 10 V, one of skill in the art will recognize that any two voltages having a differential may be used without departing from the spirit and scope of the present invention. As a result, piezoelectric transducer begins ringing at a frequency F_10V. At point1206, the voltage acrosspiezoelectric transducer1102 is suddenly decreased from, for example and without limitation, 10 V to 0 V. As a result, piezoelectric transducer changes impedance and begins ringing at a frequency F_0Vthat is different from frequency F_10V.
• The sudden changes in applied voltage instep function1202 are similar to a tuning fork being struck. As a result,piezoelectric transducer1102 rings at a self-resonance value with no additional energy applied. This makes electromechanical modulation useful for low power situations. Information bit values can be assigned to the frequencies at whichpiezoelectric transducer1102 rings. For example, the frequency at whichpiezoelectric transducer1102 rings when subject to a voltage at 10 V may indicate a “1” bit, while the frequency at whichpiezoelectric transducer1102 rings when the voltage is dropped to 0 V may indicate a “0” bit.
• An intermediate voltage may be utilized in electromechanical modulation to provide a drone frequency that separates out sequential bits in an information stream.FIG. 13 illustrates anexemplary waveform1300 for providing a high frequency, a low frequency, and a drone frequency to produce an information stream. In this example, an intermediate voltage of 5 V is used between bits to provide bit separation.Waveform1300 begins at point1302 with the application of a 5 V signal, causingpiezoelectric transducer1102 to ring at a drone frequency, f_D. At point1304, a 10 V signal is applied topiezoelectric transducer1102. As a result,piezoelectric transducer1102 resonates at a frequency f_10V, which may represent, for example, a “1” bit. At point1306, after the resonance ofpiezoelectric transducer1102 has faded due to damping inpiezoelectric transducer1102, voltage V is returned to 5 V. The drop from 10 V to 5 V causespiezoelectric transducer1102 to ring at drone frequency f_D. At point1308, a 10 V signal is applied, causingpiezoelectric transducer1102 to ring at frequency f_10Vagain, producing another “1” bit. Atpoint1310, after the resonance ofpiezoelectric transducer1102 has faded, voltage V is returned to 5 V, causingpiezoelectric transducer1102 to ring at drone frequency f_D. Atpoint1312, voltage V is dropped to 0 V. The drop causespiezoelectric transducer1102 to resonate at a frequency f_0V, which may represent, for example, a “0” bit. Atpoint1314, after the resonance ofpiezoelectric transducer1102 has faded, voltage V is returned to 5 V, causingpiezoelectric transducer1102 to ring at drone frequency f_D. In this manner,waveform1300 provides a “1-1-0” signal.
• The amount of time it takes the resonance ofpiezoelectric transducer1102 to dampen out after each voltage is applied depends on the Q of the resonator. The receiver can be set accordingly to receive the low power information communication modulated using electromechanical modulation. Sincepiezoelectric transducer1102 uses only a DC voltage in this embodiment and does not use an oscillator to drivepiezoelectric transducer1102, leakage in the circuit is similar to loss in a capacitor and the power level required is approximately 1/1000 the power required to use electromagnetic signals (such as RF).
• When a signal is transmitted fromingestible capsule104, the vibration of, for example,piezoelectric transducer1102 incommunications module204 may interfere with the operation of sensor202.Control logic604 can be configured to enable or disable operation of sensor202 and/orcommunications module204 at various times during the transit ofingestible capsule104 through, for example, the gastrointestinal tract.Control logic604 may enable or disable operation of elements ofingestible capsule104 based on time and/or location ofingestible capsule104. For example,control logic214 may include a timing module. The timing module ofcontrol logic214 may be used to enable and disable sensor202 and/orcommunication module204 in a periodic manner or at predetermined time intervals, so that sensor information is transmitted at set times.
• In an embodiment, asensor202amay interfere withsignals106, and should therefore be sampled only whensignals106 are not present in sufficient energies, such as would be adjacent tocommunications module204. For example, there may exist a standard standoff period after each information exchange that allows new, non-corrupted information to be taken by sensor202. During this standoff period, sensor202 may be activated and sensor readings read and stored. After the standoff period ends, the acoustic communications module may be re-activated for transmission. After transmission, a new standoff period begins. In another embodiment, however, sensor202 may only be valid when in the presence ofsignal106, such as with an acoustic receiver sensor to match in frequency withsignal106. In this embodiment, it is also likely that sensor202 requires a signal of comparison electrically connected tocommunications module204. Such a device results in sensing the reflectivity oftissue surrounding device104, for example, a self-contained localized ultrasonic imaging device. Additionally, such a device is efficient in that a reference signal for imagery is derived from acommunications signal106, not a separate signal requiring more power, and hence alarger device104.
• Control logic214 may be configured to gate power frompower source206 to sensor202 and/orcommunications module204, or to gate them in other manners to enable or inhibit their operation as desired. Alternatively,control logic214 may receive information from sensor(s)202 to determine a relative location ofingestible capsule104 in gastrointestinal tract300. Based on the determined location,control logic214 may enable or disable operation ofcommunications module204 and/or sensor202. Furthermore,control logic214 may also placecommunications module204 and/or sensor202 in a power conservation mode, for example a reducedpower signal106, when in close proximity to an external receiver and/or reduced sensor activity. Alternatively,control logic214 may instigate a cycle based on sensor activity and/or location.
V. Phased Array Sensor Link Module
• As described above with respect toFIG. 6,ingestible capsule104 may communicate with a sensor link module acting as an intermediary to or in lieu ofcomputing device108.Sensor link module602 may be coupled to human102 in a variety of ways. For example,sensor link module602 may be directly attached to the skin ofhuman102, such as by an adhesive or a strap.Sensor link module602 may be incorporated in a patch for direct attachment to a surface, such as skin, ofhuman102. An adhesive layer may be coupled tosensor link module602. The adhesive layer may include, for example, an adhesive commonly used in transdermal patches.
• In one embodiment, eachsensor link module602 includes a single acoustic transducer, and multiple patches can be used to triangulate the location of an ingestible capsule, receive information exchanges from the ingestible capsule, and/or transmit information to the ingestible capsule. In another embodiment, a singlesensor link module602 includes multiple acoustic transducers. The transducers are organized into an array, receive information exchanges from the ingestible capsule, and/or transmit information to the ingestible capsule. Additionally, transducers organized into an array can facilitate an accurate location, whereby phase differences between the transducers are used to calculate the direction (angle) of the ingestible capsule; in combination, amplitudes of signals between the transducers at the same or different frequencies derive distance. The combination creates an accurate location ofdevice104.
• FIG. 14 is an illustration of an exemplary phasedarray1400 for use as a sensor link module according to an embodiment of the present invention.Phased array1400 includes multiple acoustic transducers1402. AlthoughFIG. 14 illustrates an array of nine acoustic transducers1402a-1402i, one of skill in the art will recognize that any number of acoustic transducers1402 may be used without departing from the spirit and scope of the present invention. Further, one of skill in the art will recognize that acoustic transducers1402 may be placed in any pattern, such as a grid pattern or a close-packed hexagonal array pattern.
• An array of acoustic transducers1402 allows triangulation to be performed using a single sensor link module when a device, such asingestible capsule104, emits asignal1404.Signal1404 may be an information signal, such asinformation signal106, or it may be a locationing signal emitted, for example, prior to the emission ofinformation signal106. As illustrated inFIG. 14,signal1404 has various wavefronts.
• The phase of the signal detected by a given acoustic transducer1402 will vary, depending on the location ofingestible capsule104 relative to the given acoustic transducer1402. The operating wavelength λ ofingestible capsule104 determines the size and location of each acoustic transducer1402. If each acoustic transducer has a width of λ/4 and is separated from other acoustic transducers by a distance of λ/4, such that the distance between the centers of two adjacent acoustic transducers is λ/2, different phases of each signal period can be detected by the various acoustic transducers1402. The different phases and amplitudes ofsignal1404 as detected by multiple acoustic transducers1402 can then be used to pinpoint the location ofingestible capsule106 relative to the sensor link module by calculation of angle and distance from the phase and amplitude, respectively, ofsignal106 as it is received by transducers1402.
• Because the signal is acoustic, however, it can be difficult to ensure that the signal detected by transducer1402 is at its peak at a combinedreception point1408 for input toreceiver1410, which is needed for accurate locationing. To solve this difficulty, an adjustable delay1406 may be coupled to each acoustic transducer1402. In an embodiment, each adjustable delay1406 automatically adjusts itself to achieve maximum gain at a peak signal amplitude with respect to a combined signal atpoint1408, or alternatively with respect to a single reference signal such aselement1402a, similarly to a radio frequency phased array construction. In another embodiment, a separate circuit may adjust delays1402a-1402i. Detection of the peak signal amplitude at a maximum gain (thus maximizing SNR) may occur based on, for example, successive approximation or a previous location measurement. Use of a successive approximation method is possible because receivedacoustic signal1404 is moving much more slowly than the time it takes to digitally process receivedsignal1404. For example, using a 1 MHz digital signal processor, all the calculations needed to focus on the signal can be performed more quickly than the signal changes.
• For example, inFIG. 14, a first portion of a wavefront (e.g., a portion ofsignal1404 assigned a 0° phase delay) ofsignal1404 is detected byacoustic transducers1402a,1402e, and1402i. A second portion of wavefront ofsignal1404 detected byacoustic transducers1402dand1402hdiffers from the first portion of wavefront ofsignal1404 by 90°. A third portion of wavefront ofsignal1404 detected byacoustic transducer1402gdiffers from the first portion of wavefront ofsignal1404 by 180°. Therefore, the maximum gain of the signal is produced when a value of 0° is assigned to phasedelay1406g, a value of 90° is assigned to each ofphase delays1406dand1406h, and a value of 180° is assigned to each ofphase delays1406a,1406e, and1406i. To achieve the maximum gain of the system, all wavefront peaks should be aligned at the output of adjustable delays1406a-1406i.
• Once the phase footprint ofsignal1404 is determined, the phase footprint can be used to identify the location ofingestible capsule104. That is, the phase separation of the different acoustic transducers1402 identify the angular direction ofingestible capsule104 while the differences in time of arrival between acoustic transducers1402 indicate a distance toingestible capsule104.
• The same phase information can also be used to maximize the SNR of an information signal received fromingestible capsule104, such asoutput information signal106. In an embodiment, a primary wavefront fromdevice104 is phase aligned throughout all transducers1402a-1402i. However, acoustic noise is typically produced by reflections from objects within the human102 and also the exterior skin ofhuman102. Reflections likely do not originate from the same angle with respect to the array1402. Thus, the combined noise signal output atpoint1408 is reduced from maximum signal as the reflections, originating from an off-angle position, are partially phase cancelled due to the delays set upon1406a-1406i. Output information signal106 can thus be transmitted at a lower power than is required for systems that do not have as high a SNR. That is, systems that are not optimized to receive a transmitted signal at maximum gain require a higher-power transmission, in case the signal is received off-peak and/or the noise is not partially phase cancelled, making the SNR relatively low. In the present embodiment, however, the signal is received on-peak and most reflected signals are partially phase cancelled so the SNR is relatively high. The power of the signal thus need not be as strong. This technique is therefore useful in an environment where low-power signals are preferable, such as the human body where signals are passing through live tissue.
• Another advantage of the phased array design is that the potential angles of reception are extremely wide for an instance of the technology, whereas a larger receiver to provide signal gain is typically very narrow. For example, an example element nine times the size of transducer1402 would provide potentially the same gain as theFIG. 14 array; however, this occurs only whendevice104 is perpendicular to a flat receiving side of a large element. Furthermore, at an angle of 45 degrees, for example, the combined signal received by an maximized array far exceeds the output of the same single element nine times larger. This is due to the wavefront cancellation within a large element on an off-perpendicular wavefront, such as is the case for an acoustic signal transmitted and received within ahuman body102.
• Further, once the location ofingestible capsule104 is determined, phasedarray1400 can also be used to focus an information exchange signal oningestible capsule104 in order to send information from phasedarray1400 toingestible capsule104. To do this, a known phase delay1406a-1406i, such as a captured configuration from a signal reception, is implemented into a signal transmitted from anamplifier1412, with the resulting phase delayed signal routed to transducers1402a-1402irespectively. Because the transmission is focused oningestible capsule104, such that the point of maximum gain intersects with the location ofingestible capsule104, either a lower average power signal may be used. Alternatively, a less sensitive (lower power) receiver design withinsensor device104 may be used.
• Although locationing and information exchange are described inFIG. 14 with respect to a phased array in a single sensor link module, one of skill in the art will recognize that improved resolution may be provided when additional sensor link modules, each having its own phased array, are used. Furthermore, one of skill in the art will also recognize that multiple phased array devices can utilize phase-only information for the accurate determination of the location ofsensor device104, as multiple intersecting lines derived from multiple angles intersect at a point of origin of the signal fromdevice104.
• In an alternate embodiment, multiple single element receivers and/orsensor link modules602 exist and forward signals received tocomputing device108. As described earlier, a desiredsignal104 may be incident upon each ofsensor link modules602 in combination with reflections from a variety of body parts within and on (e.g., located on the skin of)human102. Therefore, acomputing device108 can create a complex mathematical model (e.g., a Fourier transform) of the complex signal received. Given a particular received frequency of operation F1 ofsensor device104,computing device108 may derive a close proximity to actual signals received by a combination of F1 at an amplitude A1, and phase P1; a second harmonic at frequency F2 (necessarily at F1×2), its amplitude A2, and phase P2, and so on for 3^rdharmonic, 4^thharmonic, and further frequencies as is well known as a Fourier transform. The closeness to actual signals is primarily a function of how many harmonics can be evaluated, and the resolution of amplitude and phase. Furthermore,computing device108 performs this Fourier transform on each of the associatedsensor link modules602. The resulting analysis can be utilized to algorithmically combine signals fromsensor link modules602 for a maximum signal reception. Additionally, it can be utilized to minimize an out of phase reflection (considered in this case as noise).
• In a further implementation of this embodiment, the resulting analysis of a receivedsignal104 atsensor link modules602 can be utilized in a reverse manner, regenerating known frequencies, phases, and amplitudes of harmonics F1, F2, F3, and so on. This Inverse Fourier transform provides an environment of three (or more) transmitted waveforms from multiplesensor link modules602 that maximally constructively interfere, with all reflection points in the body considered, at the point of the original signal received fromdevice104. Additionally, this process must be repeated for each location ofdevice104, location ofsensor link modules602 collectively, and for each transmitting frequency utilized. A person skilled in the art will recognize that the exemplified embodiment above utilizing threesensor link modules602 may also utilize any number ofsensor link modules602 to afford a desired level of accuracy, including onesensor link module602.
VI. Acoustic Biobus
• The ability to modulate information into an acoustic transmission, coupled with the ability to focus the reception and/or transmission of the signal on a particular location to achieve maximum gain makes it possible to use acoustic waves for many applications in addition to communication with an ingestible sensor device or multiple sensor devices.
• One such application is communication with and control of implanted devices, such as prosthetic controls. Currently, prosthetics require a significant amount of wires and data paths (collectively referred to herein as a wiring harness) to effect movement of the prosthetic. According to an embodiment of the present invention, an internal acoustic biobus replaces or supplements the wiring harness of the prosthetic.FIG. 15 illustrates an exemplary biobus system according to an embodiment of the present invention. A human1502 has aprosthetic limb1504. An implantedprosthetic control unit1506 receives signals frombrain1508 viaconnection1510.Prosthetic control unit1506 interprets the signals received frombrain1508 and modulates them into an instruction signal. The instruction signal is transmitted byprosthetic control unit1506 as anacoustic information signal1512.Acoustic information signal1512 is received by aprosthetic operation unit1514, which causesprosthetic limb1504 to function accordingly. An acoustic biobus in accordance with this embodiment reduces or eliminates the wiring harness used forprosthetic limb1504. Additionally, information is transmitted in a format friendly to human tissue, namely, acoustic format. Use of an acoustic biobus also reduces or eliminates the susceptability ofprosthetic limb1504 to interference from environmental noise, such as cellular telephone transmissions and many other forms of radio frequency communications common in today's society.
• Similarly, acoustic information signals may be communicated between implantable devices, such as pacemakers, and external status and control devices.
VII. Modulation and/or Demodulation Methods
• Communications module204 (FIG. 2) may be configured to modulate information fromsensor output signal212 with a carrier frequency to generateacoustic output signal106 according to a variety of modulation techniques. Such techniques include, for example and without limitation, amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), pulse-width modulation (PWM), and pulse-position modulation (PPM), and any combination of these modulation techniques, including in-quadrature or other modulation schemes. Previous schemes have been used for short commands, such as that described in U.S. Pat. No. 7,024,248 to Penner et al., incorporated herein by reference in its entirety. Such previous schemes used for short commands do not consider difficulties present in long term and/or long stream data transmission, or communication with an ingestible capsule. For example, such previous schemes do not account for the multiple acoustic reflections and noise that may interfere with longer periods of transmissions.
• Modulation schemes are also discussed in co-pending U.S. patent application Ser. No. ______, Atty. Docket No. 2520.0110001, titled “System and Method for Acoustic Information Exchange Involving an Ingestible Low Power Capsule,” and co-pending U.S. patent application Ser. No. ______, Atty. Docket No. 2520.0160000, titled “Methods and Systems for Acoustic Data Transmission,” each of which is incorporated herein by reference, both generally and as they pertain to acoustic data modulation/demodulation schemes.
• Before further discussion of specific acoustic data transmission methods, it is important to describe the general acoustic environment of the medium, in this case human102 (and similar for most animals of approximate size). Specifically, it is important to note i) how to transduce a signal, ii) what noise is to be considered, both external and internal, and iii) what methods to use to best decode the signal in the presence of the second item, noise.
• When designing a transducer, well known principles apply to matching with transmitted medium. For example, a radio frequency antenna will launch electromagnetic waves into its environment, which includes air, buildings, etc. It is designed to assume contact with a certain medium (generally air). Similarly, a design of a speaker (and enclosure) is designed to be most efficient when operational at a certain normal air pressure (such as sea level). An exemplary transducer that may be used in embodiments of the present invention assumes a characteristic environment of ahuman body102.
• Such a transducer needs to be appropriate for use within a human body, for example in contact with human tissue. Greatly different from a speaker design in contact with air, a fluid possesses a different set of characteristics. For instance, a speed of an acoustic wave in air at sea level is approx 350 meters per second. However, a speed of an acoustic wave in an animal tissue is approx 1500 meters per second. Additionally, a force required to move a volume of air is substantially different from a force required to move a volume of tissue. Thus, when designing a transducer for a human tissue, a most efficient design comes as close as possible to matching the impedance of the medium (for example, closely matching a speed of an acoustic wave).
• Additionally, it is useful for a transducer design to focus energy in the direction of a receiver for maximal use of energy. However, the transducer design needs also to be able to be efficient in energy transfer for most, if not all, potential locations of a receiver when the transducer is mobile. In the case of an ingestible sensor device, such asingestible sensor device104, in a human body, the receiver is very mobile as it transcends the full gastrointestinal tract.
• Once a signal can be efficiently transmitted into a medium, the noise in the environment should be accounted for, both from an aspect of external noise, but also an aspect of self-generated noise due to reflections from a variety of materials. When working with radio frequencies (RF), as commonly as they are used a key study is in the external impact of unwanted signals from other unknown transmitters, characterized as noise. Conversely, when evaluating an acoustic environment within a human body, very little, if any, noise is present from other transmitters, given an ultrasonic frequency range. One of very few applications of ultrasonic signals upon a human body is in the case of ultrasound—an imaging technique by use of ultrasonic signals. However, this is not present for a general population, and a patient is typically under a doctor's care when ultrasonic frequencies are being transmitted into the body. Additionally, ultrasonic frequencies used exterior to the human body would need to convey internal to the body in order to interfere with an internal transducer. Although this is possible, it is unlikely as a result of the large difference in impedance of air and human tissue. Ultrasonic frequencies, as a result, mostly bounce off the human skin to return to the air medium from which they originated.
• Additionally, some common uses of RF transcend long distances almost entirely in air, such as with cellular telephony. In these cases, reflections are reasonably spaced with respect to time, and are also very modestly attenuated with respect to power at a receiver. An ultrasonic environment within a relatively confined space, such as a human body, presents a difficult noise model. Since there are bones, air pockets, differing tissues, sacks of liquids, dynamic resonating cavity effects due to breathing, heart beat, larynx, moving fluid such as blood flow in blood vessels, etc., causing Doppler shifting, all within close proximity (tens and hundreds of wavelengths as opposed to tens and hundreds of thousands of wavelengths) to a transmitter and receiver, very complex waveforms are received at the receiver. These waveforms may be a combination of a multitude of re-transmitted waveforms in the form of reflections from the original transmitted waveform imposed upon the original waveform. Further complicating the acoustic model is the human skin. The skin is an effective reflector. As effective as the skin is in reflecting airborne ultrasonic transmissions, it also reflects a substantial amount of incident energy from within. Reflections may include a reflected original wavefront, but also a reflected complex wavefront built with all of the other reflected wavefronts from the variety of organs and materials within the body.
• Timing of these reflections leads to an evaluation in three scenarios. A first timing scenario occurs when an original waveform is received prior to any substantial reflected waveforms from the original, referred to herein as ‘clear channel’. A second timing scenario occurs during reception of some but not all of the complex wavefronts caused by some but not all of the reflections, referred to herein as ‘transitionary channel’. A third timing scenario occurs after all reflections have substantially stabilized, herein referred to as ‘standing wave channel’. It is noted that the standing wave channel is an adiabatic approximation, valid for acoustic event time periods much shorter than the dynamic changes in the resonating cavity, due to body functions such as heart beating and breathing. It is most important to note that a modulation of a carrier frequency (a traditional method of encoding data upon a frequency) in any of amplitude, frequency, or phase, imposes a same environment study as does turning a carrier on and off (the extreme of amplitude modulation). The acoustic environment may therefore be analyzed to determine clear channel, transitionary channel, and standing wave channel characteristics from the time period of the implementation of the modulation.
• Differing technologies may apply to the three differing timing scenarios described above, or potentially a combination of multiple technologies to make use of multiple timing scenarios. For example, an embodiment of the present invention utilizes frequency hopping in order to maintain operation within a first timing scenario, clear channel. For continuous operation, frequencies are changed prior to the transitionary channel. As long as the frequency being hopped to was not previously sent or is completely attenuated from a previous transmission, it will be presented with a clear channel. In another example embodiment, a system makes use of a standing wave channel. Additional details of modulation schemes according to these and other embodiments of the present invention follow.
A. Drone Frequency
• For example, in an embodiment, FM may be used to send the output information signal106 fromingestible capsule104, in a variety of schemes. For instance, an example FM protocol that can handle multiple sensors202a-202cis described below:

• FDrone=	a drone frequency,
  F0=	a frequency for bit zero,
  F1=	a frequency forbit 1,
  Fi=	an information frequency, where i = a, b, c, etc forsensors 202a-
  	202c, respectively, and
  FID=	a frequency sequence of zero bits (F0) and one bits (F1)
  	for an identification number of the particularingestible
  	sensor device
  104.

• The drone frequency F_Droneis used to provide a detectable separation between frequencies Fa, Fb, and Fc related to information from sensors202a-202c. The presence of drone frequency F_Dronemay not be required in all implementations. Frequencies Fa, Fb, and Fc may have frequency ranges that are non-overlapping so that communications related to sensors202a-202ccan be distinguished from each other. In an embodiment, after aningestible capsule104 is swallowed, the swallowedingestible capsule104 is configured to serially send out the following frequency sequence:
• F_DroneF_IDF_DroneF_aF_DroneF_bF_DroneF_cF_DroneF_IDF_Drone
• Thus, in a first time slot (F_Drone),ingestible capsule104 transmits the drone frequency F_Drone. In a second time slot (F_ID),ingestible capsule104 transmits the identification number for the particularingestible capsule104 as a series of 0 and 1 bits, respectively represented by frequencies F₀and F₁. The identification number may be useful, for example, when more than oneingestible capsule104 is transmitting from insidehuman102.
• In a third time slot (F_Drone),ingestible capsule104 transmits the drone frequency F_Drone. In a fourth time slot (F_a),ingestible capsule104 transmits information related tosensor202a. The information is transmitted at a central frequency of F_athat varies in frequency in a manner according to information from sensor output signal212a. Thus, information fromsensor202ais transmitted in the fourth time slot. In a fifth time slot (F_Drone),ingestible capsule104 transmits the drone frequency F_Drone. In a sixth time slot (F_b),ingestible capsule104 transmits information related tosensor202b. The information is transmitted at a central frequency of F_bthat varies in frequency in a manner according to information from sensor output signal212b. Thus, information fromsensor202bis transmitted in the sixth time slot. In a seventh time slot (F_Drone),ingestible capsule104 transmits the drone frequency F_Drone. In an eighth time slot (F_c),ingestible capsule104 transmits information related tosensor202c. The information is transmitted at a central frequency of F_cthat varies in frequency in a manner according to information from sensor output signal212c. Thus, information fromsensor202cis transmitted in the eighth time slot. In a ninth time slot (F_Drone),ingestible capsule104 transmits the drone frequency F_Drone. In a tenth time slot (F_ID),ingestible capsule104 transmits the identification number for the particularingestible capsule104. In an eleventh time slot (F_Drone),ingestible capsule104 transmits the drone frequency F_Drone. In subsequent time slots, information related to sensors202a-202ccan be further transmitted at frequencies F_a-F_c, and the identification number F_ID, can be further transmitted, separated by the drone frequency F_Das desired.
• This frequency sequence may be received, and due to the ordering of frequency signals, and the different frequencies used, the received information from sensors202a-202ccan be demodulated and stored in an organized manner.
• In such embodiments, information from any number of sensors202 can be accommodated. In some embodiments, the drone frequency F_Dmay not be necessary. Furthermore, in some embodiments, the identification number sequence, F_ID, may not be necessary (e.g., if identicalingestible capsules104 are individually used by human102). Any length of identification number may be used.
• A time interval, T_d, may be used for each of the time slots described above. The time interval T_dmay be bounded by a minimum time interval for T_d, T_dmin, and a maximum time interval for T_d, T_dmax. As discussed above, the minimum time interval, T_dmin, is determined by noise issues. Here, either the standing wave model or the clear channel model is employed. If the standing wave approach is applied, then the system needs to wait for the signal to stabilize to a standing wave. If the clear channel approach is chosen, then the system needs to wait for the signal to decay before sending out a new signal on the same frequency. The maximum time interval, T_dmax, may be determined by power consumption issues (such as a charge lifespan of battery702) ofingestible capsule104. Furthermore, a duty cycle, T_c, may be used for the time slots described above. The duty cycle, T_c, may be bounded by a minimum duty cycle length, T_cmin, and a maximum duty cycle length, T_cmax. The minimum duty cycle, T_cmax, may be determined by requirements of the particular diagnostic test(s) to be performed byingestible capsule104, and the maximum duty cycle, T_cmax, may be determined by power consumption issues (such as a charge lifespan of battery702) ofingestible capsule104.
B. Spread Spectrum
• i. Overview
• An embodiment of the present invention is directed to acoustically transmitting data (such as communication signal106) from a transmitter (such as ingestible capsule104) to a receiver (such as sensor link module602). In this embodiment, a high data rate is achieved by spreading acoustic data signals within a bandwidth considerably exceeding the data bandwidth. The spreading scheme is based on quasi-orthogonal spreading codes having substantially zero auto-correlation functions. Advantageously, the spreading scheme is combined with efficient modulation schemes, thereby considerably mitigating inter-symbol interference and providing reliable system performance. In addition, the spreading code and modulation schemes can be easily implemented using hardware components to reduce power consumption within and the size ofingestible capsule104.
• An acoustic transmission system according to an embodiment of the present invention includes a transmitter and a receiver. A data source provides a sequence of data symbols, which may be binary or M-ary symbols. An acoustic transmitter transforms the sequence of data symbols into an acoustic signal by an encoding procedure and acoustic carrier modulation. Sometimes the acoustic transmitter adds a preamble packet (preamble) for synchronization and channel parameters estimation at the receiving site.
• Acoustic waves, radiated by the transmitter, propagate through an acoustic channel. The acoustic waves reach the receiver by several paths, reflecting from different objects, surface areas, surface boundaries and interfaces in the environment. This multi-path propagation provides a complex interference of acoustic rays, having different attenuation, phase and delay. Each acoustic ray has instable (variable) amplitude and phase (fading) because it includes several sub-rays with insignificant delay variations.
• An acoustic receiver receives random noise and the acoustic signals transmitted by the transmitter. The acoustic receiver transforms the additive mixture of noise and delayed signals into data symbols using a demodulation and decoding procedure as described herein.
• ii. An Example System
• FIG. 17 depicts a block diagram illustrating an example acoustic data transmission system according to an embodiment of the present invention. The acoustic data transmission system ofFIG. 17 includes atransmission path1701 and a receivepath1751. In an embodiment,transmission path1701 is included iningestible capsule104 and receivepath1751 is included insensor link module602.
• Transmission path1701 includes anencoder1710, amodulator1712, aspreader1714, and an acoustic transducer (transmitter)1716.Transmission path1701 serves to encode and modulate data to generate an acoustic signal that is transmitted through the body ofhuman102. Each element oftransmission path1701 is described in more detail below.
• Encoder1710 encodes data symbols from a data source (such as sensor output signal212). The encoding scheme may include discrete transformations of data symbols, including adding redundant symbols for forward error correction (FEC).
• Modulator1712 modulates the encoded discrete signal with a carrier. In an embodiment,modulator1712 uses a narrow band modulation scheme, such as phase shift keying (PSK), frequency shift keying (FSK), quadrature amplitude modulation (QAM), or the like, as described in more detail below.Modulator1712 includes a carrier generator (not shown).
• Spreader1714 spreads the modulated signal according to a spreading code, causing the modulated signal to be spread within a bandwidth that considerably exceeds the data bandwidth. In an embodiment, a spectrum of the modulated signal is increased by a factor of N, wherein N is the spreading factor ofspreader1714. Characteristics of the spreading code implemented byspreader1714 are described below.
• An ideal orthogonal spreading code sequence would completely eliminate any interference between a signal S_r(t) and a time delayed version of that signal S_r(t+τ). Mathematically, the amplitude A of the interference between an ideal orthogonal spreading code satisfies the following equation:
• $\begin{array}{cc}A=\frac{1}{T}{\int }_0^TS_r\left(t\right)S_r\left(t+\tau \right)t=0,\mathrm{for}\mathrm{any}\tau >T/N& \left(\mathrm{Eq}.1\right)\end{array}$
• where [0,T] is the data symbol interval, T is the data symbol duration, and N is the spreading factor.
• Rather than implementing the ideal orthogonal spreading code of equation (1),spreader1714 implements a quasi-orthogonal spreading code. The quasi-orthogonal code implemented byspreader1714 reduces interference between a signal B_r(t) and a time-delayed signal B_r(t+τ) by a factor of N, wherein N is the spreading factor. In an embodiment,spreader1714 implements a quasi-orthogonal Barker code B(t), satisfying the following equation:
• $\begin{array}{cc}A=\frac{1}{T}{\int }_0^TB\left(t\right)B\left(t+\tau \right)t=N,\mathrm{for}\mathrm{any}\tau =0& \left(\mathrm{Eq}.2a\right)\\ A=\frac{1}{T}{\int }_0^TB\left(t\right)B\left(t+\tau \right)t\le 1,\mathrm{for}\mathrm{any}\tau >T/N& \left(\mathrm{Eq}.2b\right)\end{array}$
• In this case spreading factor N is a number of binary elements ±1 within the Barker sequence (within the data symbol interval T). Equation (2) shows that side lobes of the Barker autocorrelation function do not exceed the N-th fraction of the main lobe. Thus, all widespread acoustic rays (i.e., rays which are time-delayed by more than a factor of T/N relative to the Barker sequence in the receiver) are suppressed by N times.
• Spreader1714 implements the spreading code by one or more linear operations. These linear (parametric) operations may simply comprise multiplication of the modulated signal and a spreading code sequence as described below, although other methods for spreading the modulated signal may be realized without deviating from the spirit and scope of the present invention. In an embodiment,spreader1714 implements an 11 element Barker sequence, as described in more detail below. Other Barker sequences may be used. There are Barker sequences for N=2, 3, 4, 5, 7, 11, 13. For N>13 there are not quasi-orthogonal binary sequences with A≦1. Nevertheless there are sequences with length up to N=28 for A≦2, and sequences with length up to N=34 for A≦3. For larger N, linear recurrent M-sequences (pseudo-random binary sequences) may be used for signal spectrum spreading; they provide about √N times suppression of the delayed rays.
• Returning toFIG. 17, the signal from the output ofspreader1714, having N times more bandwidth than the data symbol spectrum, is fed to acoustic transducer/Tx1716 (such as acoustic transducer904 described above). Acoustic transducer/Tx1716 converts the electrical signals fromtransmission path1701 into acoustic signals which are then transmitted through the multi-path acoustic channel in the body ofhuman102.
• After traveling through the multi-path acoustic channel, the acoustic signal is received by receivepath1751 illustrated inFIG. 17. Receivepath1751 includes an acoustic transducer (receiver)1760, a de-spreader1762, ademodulator1764, and adecoder1766. At the receiving site, the signal from the output of acoustic transducer/Rx1760 is subjected to the opposite sequence of transformations compared totransmission path1701. Although the sequence of transformations is reversed, the implementation of each method may differ substantially asingestible capsule104 is designed to be small and low power, while the same constraints do not necessarily apply tosensor link module602. A variety of implementations for transmit and receive paths are anticipated and do not depart from the spirit and scope of this invention.De-spreader1762 transforms the received wideband signal into the initial narrowband modulated signal by synchronized multiplication of the wideband signal with the spreading code.Demodulator1764 demodulates the narrowband signal using signal processing based on coherent or non-coherent detection schemes.Decoder1766 distinguishes data symbols from the demodulated signals, based on soft or hard decision decoding procedures. It should be noted that both de-spreader1762 anddemodulator1764 are controlled by a synchronization function (not shown in theFIG. 17).
• It is to be appreciated thattransmission path1701 and receivepath1751 are presented for illustrative purposes only, and not limitation. Variations oftransmission path1701 and/or receivepath1751 can be implemented without deviating from the spirit and scope of the present invention. For example,modulator1712 can be implemented afterspreader1714. As another example, some filtration elements—such as a band-pass filter (BPF) or low-pass filter (LPF)—may be used in bothtransmission path1701 and receivepath1751. In such examples, a narrowband BPF is used after de-spreader1762. Such filtration elements are not depicted inFIG. 17, although their inclusion is within the spirit and scope of the present invention, as would be apparent to a person skilled in the relevant art(s).
• iii. Example Encoding Schemes
• (a) Phase Shift Keying
• FIGS. 18 and 19 depict block diagrams respectively illustrating a transmission path and a receive path of an acoustic data transmission system based on PSK modulation in combination with a spreading code according to an embodiment of the present invention. The transmission path ofFIG. 18 may be implemented iningestible capsule104 and the receive path ofFIG. 19 may be implemented in an external receiver patch, such assensor link module602.
• Referring toFIG. 18, the transmission path includes aPSK encoder1810, aPSK modulator1812, acarrier generator1813, a spreading code generator (SCG)1814, amultiplier1815, and an acoustic transducer/Tx1816.PSK encoder1810 together withPSK modulator1812 andcarrier generator1813 provide the phase modulated signals. The particular functions ofPSK encoder1810 andPSK modulator1812 depend on the type of PSK modulation scheme—whether binary PSK, binary differential PSK, M-ary PSK or M-ary DPSK, or the like. For example, if the modulation scheme is implemented as binary PSK, thenPSK encoder1810 andPSK modulator1812 may be implemented as a simple logic multiplier. If the PSK modulation scheme is implemented as DBPSK, thenPSK encoder1810 includes a binary multiplier and a binary delay element (see, e.g.,FIGS. 20 and 22 below), andPSK modulator1812 includes a simple multiplier. In the case of M-ary PSK or M-ary DPSK, for instance, QPSK or DQPSK,PSK encoder1810 may be implemented as a Gray-code encoder, andPSK modulator1812 may be implemented as an I/Q modulator according to known schemes.
• The phase modulated carrier from the output ofPSK modulator1812 is fed tomultiplier1815, where it is multiplied by the spreading sequence, generated bySCG1814.SCG1814 generates the spreading sequence synchronously with the modulated symbols at the output ofPSK modulator1812.
• The wideband signal at the output ofmultiplier1815 is fed to acoustic transducer/Tx1816. Acoustic transducer/Tx1816 transmits the acoustic signal into the multi-path acoustic channel as described above.
• After traveling through the multi-path acoustic channel, the acoustic signal is received by the receive path ofFIG. 19. The receive path includes an acoustic transducer/Rx1960, amultiplier1941, aSCG1942, a synchronization unit (synch)1943, and aPSK demodulator1964. Acoustic transducer/Rx1960 receives the acoustic signal and converts it into an electrical signal.SCG1942 andPSK demodulator1964 are controlled bysynch1943, which uses both the received signal from the output of acoustic transducer/Rx1960 and output signals fromPSK demodulator1964. The particular functions and schemes ofPSK demodulator1964 depend on both the PSK type and signal processing algorithm. For example, if it is PSK, the conventional coherent scheme based on the carrier recovery technique is used. If it is DPSK, the conventional I/Q non-coherent scheme or even the simplest autocorrelation scheme may be used.
• (b) Differential Phase Shift Keying
• FIGS. 20 and 21 depict block diagrams respectively illustrating a transmission path and a receive path of an acoustic data transmission system based on DBPSK in combination with a Barker spreading code according to an embodiment of the present invention. The transmission path ofFIG. 20 may be implemented iningestible capsule104 and the receive path ofFIG. 21 may be implemented in an external receiver patch, such assensor link module602.
• The transmission path ofFIG. 20 includes amultiplier2002, adelay element2004, amultiplier2006, aBarker code generator2008, amultiplier2022, acarrier generator2013, and an acoustic transducer/Tx2016. Referring toFIG. 20, the DBPSK encoder includesmultiplier2002 and a (one bit)delay element2004. In this scheme, a current data bit b_kin form of ±1 is multiplied by a result of a previous multiplication e_k−1after it goes throughdelay element2004. Thus, the encoded bit e_kthat is submitted tomultiplier2006 can be written as
• 
  e_k=e_k−1*b_k  (Eq. 3)
• Barker code generator2008 generates a Barker sequence. The encoded bit e_kat the output ofmultiplier2002 is subdivided into N equal parts by multiplication with the Barker sequence, containing N positive and negative ones, inmultiplier2006.Carrier generator2013 generates a carrier. The spreaded signal from the output ofmultiplier2006, containing N positive and negative ones, modulates the carrier inmultiplier2022. The modulated carrier is fed to acoustic transducer/Tx2016 and transmitted into the multi-path acoustic channel.
• After traveling through the multi-path acoustic channel, the acoustic signal is received by the receive path ofFIG. 21. The receive path includes an acoustic transducer/Rx2160, amultiplier2141, aBarker code generator2142, asynch2143, and ademodulator2164. Acoustic transducer/Rx2160 receives the acoustic signal and converts it into an electrical signal.Barker code generator2142 anddemodulator2164 are controlled bysynch2143, which uses both the received signal from the output of acoustic transducer/Rx2160 and the output signals fromdemodulator2164. As illustrated inFIG. 21,demodulator2164 is implemented as an I/Q DBPSK non-coherent demodulator, which provides a substantially perfect bit error rate (BER). In this embodiment, the BER is very close to the minimum possible BER (for example, BER=10⁻³at SNR≈8.0 dB), at the comparatively simple implementation, which does not include any carrier recovery procedure.
• (c) First Order And Second Order Differential Phase Shift Keying
• An embodiment of the present invention uses both first order and second order differential phase shift keying (DPSK). Such an embodiment may be implemented in combination with a spreading code, such as a Barker spreading code described herein. Using first and second order DPSK provides several advantages over conventional DPSK as described in more detail below.
• (1) Carrier Frequency Instability Problem
• Digital phase-modulated signals—such as BPSK and quadrature phase-shift-keying (QPSK)—potentially provide the highest possible performance (i.e., the lowest BER) in noisy channels, as well as in fading noisy channels. However, there are some well known difficulties for PSK technique application in channels with carrier frequency instability. If the carrier frequency changes slowly, the problem is conventionally solved by one or more of the following methods: (i) adaptive adjustment of the reference signal (carrier recovery techniques) at the receiver; (ii) periodical transmission of the reference signal (package preamble); and/or (iii) constant transmission of the reference signal in parallel with the data signal. Method (iii) is used in most advanced mobile wireless standards, such as WiFi, WiMax, LTE, and the like. Although these methods provide some advantages, they all decrease the data transmission performance and complicate the overall data transmission system.
• Embodiments of the present invention that use PSK modulation in acoustic data transmission are also complicated by carrier frequency instability. In such embodiments, there are two main sources of the carrier frequency instability.
• The first one is instability of carrier generation. For proper data transmission, the carrier frequency instability should be less than 10⁻⁴in order to achieve a nominal bit error rate, for example. If the nominal carrier frequency F is equal to approximately 1 MHz and symbol duration T is equal to approximately 200 μs (10 kbit/s at QPSK), then the phase shift Δφ will be given by
• 
  Δφ=2πΔFT=2π*100*200*10⁻⁶

  

  7.2°.
• This phase shift does not destroy the system, but considerably decreases its performance. For example, in a conventional PSK system an instability of carrier generation equal to 10⁻³completely degrades data transmission.
• The second source of the carrier frequency instability in acoustic systems is the Doppler Effect. For example, ifingestible capsule104 moves withspeed 10 cm/s, then the frequency shift ΔF is
• 
  ΔF

  

  (0.1/1500)*10⁶

  

  67 Hz,
• and the phase shift Δφ is
• 
  Δφ=2πΔFT=2π*67*200*10⁻⁶=4.80.
• So, the total phase shift, caused by both the Doppler Effect and carrier generation instability, is about 12 degrees—i.e., about 27% of minimum distance between signal vectors at QPSK—and therefore carrier frequency instability is an important problem to overcome in PSK-based acoustic data transmission systems of embodiments of the present invention.
• The above-mentioned methods for addressing the carrier frequency instability problem consume a significant amount of power, and are therefore not desirable for implementation in acoustic data transmission systems of the present invention. Thus, an embodiment of the present invention provides a solution to the above-mentioned carrier frequency instability problem by changing the PSK signal structure, without complicating the acoustic transmitter and with few additions to the acoustic receiver.
• (2) Acoustic Data Transmission Based on Two Types of DPSK
• Embodiments of the present invention include an acoustic data transmission system based on two types of DPSK techniques: (i) D¹PSK, the first order DPSK, modulates the first finite differences of the carrier phase in the acoustic transmitter; and (ii) D²PSK, the second order DPSK, modulates the second finite differences of the carrier phase in the acoustic transmitter. At the receiving site, the acoustic receiver does not use any carrier recovery techniques or adaptive frequency/phase adjustment procedures, but rather is based on direct calculation of current carrier phase (i.e., as it is in the acoustic channel).
• Advantageously, these embodiments of the present invention are substantially independent of carrier phase offset (i.e., substantially invariant to the initial phase shift in the acoustic system) at both D¹PSK and D²PSK. In addition, these embodiments include a two-mode transmitter (D¹PSK or D²PSK) based on a simple universal differential encoder and conventional carrier phase modulator. Moreover, these embodiments include a D²PSK receiver, providing both D¹PSK and D²PSK signal processing, based on a simple double-differential autocorrelation decoder with only symbol synchronization and without any carrier synchronization.
• FIGS. 25 and 26 depict block diagrams respectively illustrating a transmission path and a receive path of an acoustic transmission system that uses two types of DPSK according to an embodiment of the present invention. The transmission path ofFIG. 25 may be implemented iningestible capsule104 and the receive path ofFIG. 26 may implemented in an external receiver patch, such assensor link module602.
• Referring toFIG. 25, the transmission path includes a firstdifferential encoder2510, a seconddifferential encoder2520, amultiplier2530, acarrier generator2540, and an acoustic transducer/Tx2516. Firstdifferential encoder2510 includes amultiplier2512 and a (one bit)delay element2514. In this scheme, a current data bit b_kin form of ±1 is multiplied by a result of a previous multiplication e_k−1after it goes throughdelay element2514. Thus, the encoded bit e_kfrom firstdifferential encoder2510 can be written as
• 
  e_k=e_k−1*b_k  (Eq. 4)
• Seconddifferential encoder2520 includes amultiplier2522 and a (one-bit)delay element2524. The encoded bit e_kfrom firstdifferential encoder2510 is multiplied by a result of a previous multiplication f_k−1after it goes throughdelay element2524. Thus, the encoded bit f_kfrom seconddifferential encoder2520 can be written as
• 
  f_k=f_k−1*e_k  (Eq. 5)
The encoded bit from seconddifferential encoder2520 is then provided tomultiplier2530.
• Multiplier2530 multiplies the encoded bit from seconddifferential encoder2520 with the signal fromcarrier generator2540. The signal frommultiplier2530 is fed to acoustic transducer/Tx2516.
• Acoustic transducer/Tx2516 converts the received signal into an acoustic signal that is transmitted through the multi-path acoustic channel.
• After traveling through the multi-path acoustic channel, the acoustic signal is received by the receive path ofFIG. 26. The receive path includes an acoustic transducer/Rx2660, a double-differential autocorrelation decoder2666, asynch2670, and adecision module2676. Acoustic transducer/Rx2660 receives the acoustic signal and converts it into an electrical signal.Decoder2666 directly calculates cos/sin trigonometric functions (I/Q components) of the first and second order phase differences for the received signal (modulated carrier) in a well-known manner. The received signal from the output of acoustic transducer/Rx2660 is fed todecoder2666 and tosynch2670. I/Q components from the output ofdecoder2666 are fed todecision module2676 for making a decision regarding the transmitted data symbol.Decoder2666 anddecision module2676 are controlled bysynch2670.
• It is to be appreciated that the acoustic transmission system illustrated inFIGS. 25 and 26 is presented for illustrative purposes only, and not limitation. For example, other embodiments may include an acoustic data transmission system with a quadrature DPSK modulation scheme (D¹QPSK and D²QPSK). Such embodiments include a corresponding acoustic transmitter and receiver as would be apparent from the description contained herein. Additional embodiments may include a simple structure of a preamble signal, providing initial detection and synchronization for the data transmission session, as well as phase initialization for both D¹PSK and D²PSK modes. Further embodiments use the trigonometric functions of the first and second order phase differences at the outputs of the autocorrelation demodulator for estimation of characteristics of current movement and location ofingestible capsule104.
• Thus, an embodiment of the present invention uses two types of DPSK encoding to provide an efficient solution for carrier phase uncertainty and carrier frequency instability in acoustic data transmission systems. These embodiments are substantially independent of carrier phase offset and of carrier frequency offset (substantially invariant to phase and frequency shifts in the acoustic channel). Also, these embodiments provide a high level of data transmission robustness (e.g., a high signal-to-noise ratio), associated with the PSK modulation technique.
• (iv) Example Acoustic Data Transmission Within Human Body
• FIGS. 22 and 23 depict block diagrams respectively illustrating a transmission path and a receive path of an acoustic data transmission system for acoustically transmitting data through a human's body according to an embodiment of the present invention. The transmission path ofFIG. 22 may be implemented iningestible capsule104 and the receive path ofFIG. 23 may be implemented in an external computing device, such assensor link module602. The acoustic transmission system illustrated inFIGS. 22 and 23 is based on a DBPSK modulation scheme in combination with an 11-element Barker code (11-Barker). For illustrative purposes, the acoustic transmission system ofFIGS. 22 and 23 is described below in terms of data transmission having a bit rate of 10 kbit/s at 1 MHz carrier frequency through the acoustic channel with approximately 100 μs pulse response.
• Referring toFIG. 22, the transmission path includes aDBPSK encoder2200, amultiplier2206, an 11-Barker register2208, acarrier generator2213, and an acoustic transducer/Tx2216. The DBPSK encoder includes amultiplier2202 and a (one-bit)delay element2204. The DBPSK encoder functions in a similar manner tomultiplier2002 anddelay element2004 described above with reference toFIG. 20. For example, data bits in the form of ±1 with a bit rate of 10 kbit/s are fed to the input of the DBPSK encoder. The DBPSK includesmultiplier2202 anddelay element2204, which has a delay of approximately T=100 μs. Each current bit is multiplied by a result of the previous multiplication, as described above.
• Barker register2208 provides a Barker spreading code. The current ±1 signal (with duration 100 μs at the output of multiplier2206) is transformed into a wideband sequence of positive and negative ones (each having a duration of approximately 100/11≈19.1 μs) by multiplication with the Barker sequence (generated by Barker register2208). Barker register2208 is an 11-bit cyclic shift register, containing ±1 binary digits as illustrated inFIG. 22. Barker register2208 provides bit cyclic shifting with frequency 110 kHz, and therefore exactly 11 Barker elements are within the 100 μs data symbol interval. Barker register2208 is synchronized with the data bit interval.
• Carrier generator2213 provides a 1 MHz carrier. The spreaded signal from the output ofmultiplier2206, containing 11 positive and negative ones, modulates the 1 MHz carrier inmultiplier2222. The bit interval contains 100 cycles of the carrier, and Barker register2208 contains about 9 carrier cycles.
• The modulated carrier frommultiplier2222 is fed into acoustic transducer/Tx2216. Acoustic transducer/Tx2216 transmits an acoustic signal into the multi-path acoustic channel withinhuman102.
• After traveling through the multi-path acoustic channel, the acoustic signal is received by the receive path ofFIG. 23. The receive path includes an acoustic transducer/Rx2360, an 11-Barker register2342, a first band-pass filter2352 and a second band-pass filter2356, anautocorrelation DBPSK demodulator2359, and asynch unit2343.
• Acoustic transducer/Rx2360 receives the acoustic signal and transforms it into an electrical signal. The received signal from the output of transducer/Rx2360 first passes through firstband pass filter2352. Firstband pass filter2352 includes a wideband filter BPF₁with a bandwidth of about 110 kHz around the 1 MHz carrier frequency.
• The filtered signal is then multiplied, inmultiplier2341, by the Barker code from 11-Barker register2342. 11-Barker register2342 functions in a similar manner to Barker register2208 (FIG. 22) described above.
• The convoluted signal from the output ofmultiplier2341 passes through secondband pass filter2356. Secondband pass filter2356 includes a narrowband filter BPF₂with a bandwidth of about 10 kHz around the 1 MHz carrier frequency. The signal is then fed into the autocorrelation demodulator2309.
• Autocorrelation demodulator2309 includes adelay element2358, amultiplier2354, anintegrator2352, and a sign detector (Sgn)2380.Delay element2358 has a time delay of approximately T=100 μs. It should be noted thatdelay element2358 ofFIG. 23 differs fromdelay element2204 ofFIG. 22. In the DBPSK encoder ofFIG. 22,delay element2204 functions as a bit memory; whereas, in the autocorrelation demodulator ofFIG. 23,delay element2358 functions as a delay line (samples memory).
• In an embodiment, autocorrelation demodulator2309 operates in the following manner.Multiplier2354 multiplies the current input signal with the 100 μs delayed signal fromdelay element2358.Integrator2352 integrates (accumulates) the product during bit interval T=100 μs.
• Sgn2380 determines the received bit based on the sign of the integral. For example, a positive sign (“+”) corresponds to a bit value of 1, and a negative sign (“−”) corresponds to a bit value of 0.
• Importantly, the above-described demodulation scheme does not require generation of the carrier and does not require any reference signal at all. Rather, the above-described demodulation scheme uses an initial synchronization ofBarker register2342 and the current symbol synchronization of bothBarker register2342 andintegrator2352 in the autocorrelation demodulator. At the ideal synchronization in the additive white Gaussian noise (AWGN) channel the demodulator provides a BER=10⁻³at SNR≈8.5 dB.
• In an embodiment, a special preamble can be used for initial synchronization ofBarker register2342. The preamble, which contains at least two Barker sequences, is followed by a data package. During data package transmission, the symbol synchronization is carried out bysynch unit2343, using signals from the output of the demodulator.
• (v) Improved Signal-to-Noise Ratio Based on Multi-Path Acoustic Signals
• An embodiment of the present invention distinguishes different reflected acoustic rays to extract the ray with a high signal-to-noise ratio (SNR). This embodiment uses nearly all reflected acoustic rays by (i) initially distinguishing the acoustic rays having different time delays, (ii) accumulating signals of the acoustic rays in space divided receivers, and (iii) making a final decision based on a combined (integral) signal of the space divided receivers. The improved SNR can be achieved by a plurality of receive paths as illustrated inFIG. 24 which receive an acoustic signal after it travels through a multi-path acoustic channel. The acoustic signal can be transmitted through the multi-path acoustic channel using a transmitter similar to those described herein.
• Referring toFIG. 24, the plurality of receive paths include an acoustic transducer/Rx2460, a plurality of SCGs generating shifted versions of the spreading code, a corresponding plurality of demodulators, a plurality of SNR estimators, a plurality of weighted accumulators of the demodulator's outputs, a decision block (integrator)2470, and asynch unit2465. As illustrated inFIG. 24, the plurality of SCGs include aSCG₁2421, aSCG₂2422, and aSCG_N2423; the plurality of demodulators include a demodulator,2431, ademodulator₂2432, and ademodulator_N2433; the plurality of SNR estimators include aSNR estimator2451, aSNR estimator2452 and aSNR estimator2453. Each receive path ofFIG. 24 includes a SCG, a demodulator, and SNR estimator. For simplicity of exposition, the operation ofSCG₁2421,demodulator₁2431, andSNR estimator2451 is described below. The operation of the other SCGs, demodulators, and SNR estimators will be apparent from this description.
• Acoustic transducer/Rx2460 receives the acoustic signal after it travels through the multi-path acoustic channel.Multiplier2411 multiplies the received signal from the output of acoustic transducer/Rx2460 by the shifted signals from the output ofSCG₁2421, and provides the result todemodulator₁2431.
• SNR estimator2451 estimates the SNR of the received acoustic signal.Multiplier2441 multiplies the soft decisions from the output ofdemodulator₁2431 by the weight coefficient w₁provided bySNR estimator2451, and provides the result tointegrator2470.
• Integrator2470 combines the final signal from each receive path for making a hard decision regarding the transmitted data symbol. The SCGs and the demodulators are controlled bysynch unit2465 in a similar manner to that described above.
• The plurality of receive paths ofFIG. 24 combine a plurality of reflected rays in the multi-path acoustic channel to provide an output signal having a high SNR, thereby providing improved performance.
• Another embodiment combines the received data signal from each of a plurality of receivers (e.g. sensor link modules602) having space diversity. The plurality of spatially diverse receivers can be used in different manners. According to a first approach, the final (integral) signal from each spatially diverse receiver (as described above with reference toFIG. 24) is combined (with corresponding weighted coefficients) into a super-signal, which serves as a basis for hard decision making. This approach provides a very high performance gain. A second approach provides signal processing in each spatially diverse receiver with only (individual) shift of the spreading code, and after that the outputs of the spatially diverse receivers are combined (with corresponding weighted coefficients) into a final (integral) signal for hard decision making. According to a third approach, the individual receivers find out in turn (in order of priority) the biggest next reflection and use a combination of the found reflections for making the final hard decision.
• It is important to note that the exemplary frequency band of operation around 1 MHz is presented for illustrative purposes only, and not limitation. Persons skilled in the relevant art(s) will appreciate that a higher data rate, for example 2 times illustrated above, can be realized based on the teachings above, translated into, for example, a 2 MHz frequency band of operation. Such deviations from the teachings above are contemplated within the spirit and scope of this invention.
• Furthermore, higher data rates may be achieved in accordance with an embodiment of the present invention by operating multiple parallel data paths or a single data path split into multiple data paths, wherein each is or many data paths are implemented through the methods described and exemplified above and operational on discrete and disjoint frequency bands. For example, from teachings and examples above, and with reference toFIG. 9, transducer904A may be operational at 1 MHz, with a bandwidth of 100 kHz, and a data rate of 10 kbps. Additionally, transducer904B may operate at 1.2 MHz, with 100 kHz of bandwidth and 10 kbps data rate.Device104, if operating transducers904A and904B concurrently, can achieve a data rate of 20 kbps to an external set of receivers. A person skilled in the relevant art(s) will appreciate how to design a system with a plurality of transmitters and receivers in parallel operation to achieve a targeted data bit rate without depart from the spirit and scope of this present invention. For example, a plurality of orthogonal spreading codes may be used in combination with a single acoustic transducer to transmit through a corresponding plurality of acoustic channels, thereby increasing the data rate of transmission.
C. Frequency Hopping
• i. Overview
• FIG. 27 illustrates a frequency hopping (FH) scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention. Anacoustic communication signal2700, such ascommunication signal106, may be transmitted from a transmitter, such asingestible capsule104, to a receiver, such asexternal computing device108 or one or moresensor link modules602 attached to the skin of the body, using the FH scheme. The FH scheme encodes and/or decodes communication signals by switching a carrier frequency among one or more frequency channels. The carrier frequency used to encode and/or decode the acoustic communication signal is changed or hopped over a range of frequencies according to a chosen code known as a hopping pattern.
• As shown inFIG. 27, anacoustic communication signal2700 may be partitioned into one or more time intervals denoted as t₁through t_N. Time intervals t₁through t_Nmay represent the duration of a bit, a byte, a symbol, a session, or any other suitable time interval that will be apparent to those skilled in the relevant art. Each time interval t₁through t_Nincludes a corresponding frequency channel denoted as ch₁through ch_N. In an exemplary embodiment, an initialization frequency channel, such as frequency channel ch₁, is reserved as a data sequence initiation signal or a synchronization signal between the transmitter and the receiver. After transmission of the acoustic communication signal, the transmitter transmits the initialization frequency channel to allow for transmission of a next acoustic communication signal. Upon detection of the initialization frequency channel, the receiver switches a corresponding carrier frequency to a carrier frequency associated with the initial frequency channel to begin decoding of the next acoustic communication signal.
• The FH scheme selects or switches among frequency channels ch₁through ch_Nbased upon time intervals t₁through t_Nto encode and/or decodeacoustic communication signal2700. For example, frequency channel ch₁is selected for time interval t₁. After time interval t₁lapses or expires, frequency channel ch₂is selected for time interval t₂. The transition between a first frequency channel, such as frequency channel ch₁and a second frequency channel, such as frequency channel ch₂, may be substantially instantaneous, as shown inFIG. 27, or delayed. Likewise, as time interval t₂expires, frequency channel ch₃is selected for time interval t₃. Each of remaining frequency channels ch₄through ch_Nis selected for a corresponding time interval t₄through t_Nin a similar manner. Upon expiration of time interval t_N, frequency channel ch₁is selected once again to continue switching among frequency channels ch₁through ch_Nbased upon time intervals t₁through t_N.
• In an exemplary embodiment, a maximum duration of time intervals t₁through t_Nis such that the information content embedded with a corresponding frequency channel is transmitted and/or received before the acoustic multipath phenomena generates a second considerable residual ray, described previously as the clear channel, for that particular frequency in a target environment, such ashuman102. The second considerable ray represents the first reflection of the transmitted communication signal generated by the multipath phenomena, and starts the time period of a transitionary channel. In this exemplary embodiment, the duration (T) for each time interval t₁, through t_Nmay be given by:
• $\begin{array}{cc}T=\frac{T_{\mathrm{RAY}}}{\mathrm{NUM\_CH}},& \left(\mathrm{Eq}.5\right)\end{array}$
• where T_RAYrepresents a truncated ray delay and NUM_CH represents the number of frequency channels in frequency channels ch₁through ch_N. The truncated ray delay represents an amount of time necessary for all rays generated by the multipath phenomena for a corresponding frequency to be attenuated to a negligible level, such as, but not limited to, fifteen decibels (dB) to provide an example. In an exemplary embodiment suitable for use inhuman102 and at a particular ultrasonic frequency range, the truncated ray delay may be, for example, approximately equal to from 100 to 200 microseconds. However, this example is not limiting, and other maximum durations for time intervals t₁, through t_Nthat are apparent to those skilled in the relevant art are within the scope and spirit of the present invention.
• From the discussion above, the multipath phenomena may causeacoustic communication signal2700 to reach the receiver by one or more paths. Switching from a frequency channel, such as frequency channel ch₁, to another frequency channel, such as frequency channel ch₂, before generation of the second considerable ray mitigates the effects of the multipath phenomena. In addition, cyclic repetition of frequency channels ch₁through ch_Nafter at least T*NUM_CH seconds, allows the transmitter and/or the receiver to reuse frequency channels ch₁through ch_Nafter all considerable rays from a corresponding frequency channel ch₁through ch_Nhave become negligible, returning the frequency of interest to a clear channel status. For example, the transmitter may once again select the corresponding carrier frequency associated with frequency channel ch₁after at least T*NUM_CH seconds has elapsed to allow the second considerable residual ray and all other considerable rays to attenuate to a negligible level.
• FIG. 28 illustrates a hopping pattern used to encode and/or decode the acoustic communication signal according to an exemplary embodiment of the present invention. The hopping pattern may be represented by a time-frequency matrix. The time-frequency matrix is a graphical representation of carrier frequencies, denoted as f₁through f_M, that may be assigned to a corresponding frequency channel ch₁through ch_N. Each frequency channel in frequency channel ch₁through ch_Nneed not contain a corresponding carrier frequency. For example, carrier frequency f₁may be assigned to frequency channel ch₁. In other words, carrier frequency f₁is used for the encoding and/or decoding of the acoustic communication signal during the time interval t₁corresponding to frequency channel ch₁. Likewise, carrier frequency f_Mmay be assigned to frequency channel ch₂. Similarly, carrier frequency f₃may be assigned to frequency channel ch₃. Finally, carrier frequency f₃may be assigned to frequency channel ch_N. However, this example is not limiting, those skilled in the arts will recognize that frequency channels ch₁through ch_Nmay assigned to any other suitable sequence of carrier frequencies f₁through f_Mwithout departing from the spirit and scope of the invention. For example, any suitable random or pseudo-random sequence may be used to assign carrier frequencies f₁through f_Mto the corresponding frequency channel ch₁through ch_N. As another example, carrier frequencies f₁through f_Mmay be assigned to the corresponding frequency channel ch₁through ch_Nin a sequential manner with a carrier frequency having a least frequency being assigned to frequency channel ch₁and a carrier frequency having a greatest frequency being assigned to frequency channel ch_N. In a further example, an identification of the transmitter and/or the receiver, such as but not limited to an electronic identification, may be used to assign carrier frequencies f₁through f_Mto the corresponding frequency channel ch₁through ch_N. In this example, the identification of the transmitter and/or the receiver is unique for each transmitter and/or receiver thereby encrypting the acoustic communication signal based on the hopping pattern. A further example is having no frequency used more than once in channels ch₁through ch_Nto ensure that each frequency has a clear channel. Furthermore, in an embodiment using encrypted information, a transmitter may send a signal on a frequency that is not part of the matrix. This additional information intentionally obscures the real information.
• ii. Combination of Frequency Hopping and Pulse Interval Encoding
• FIG. 29A illustrates a combined FH and pulse interval encoding (PIE) scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention. Anacoustic communication signal2900 may represent an exemplary embodiment ofcommunication signal106. From the discussion ofFIG. 27 above, a transmitter, such ascommunications module204, transmitsacoustic communication signal2900 by encoding an information signal, such assensor output signal212, onto frequency channels ch₁through ch_Ncorresponding to time intervals t₁through t_N. The transmitter delays the transmission of adjacent frequency channels, such as frequency channel ch₁and frequency channel ch₂, by a corresponding time delay T₁through T_Nto encode the information signal.
• As shown inFIG. 29A, the transmitter transmits a first frequency channel, such as frequency channel ch₁, for a first interval of time, such as time interval t₁. The transmitter then waits or ceases to transmit for a corresponding time delay, such as time delay T₁, to begin the transmission of a second frequency channel, such as frequency channel ch₂. The transmitter encodes the information signal by varying a length of the corresponding time delay T₁. More specifically, the transmitter encodes the information signal by delaying the transmission of the second frequency channel a number of delay intervals i₁through i_k. The number of delay intervals i₁through i_kincluded within a corresponding time delay T₁through T_Nrepresents a logic value. The logic value may be one or more bits, one or more bytes, one or more symbols, or any other suitable data length or combination of data lengths. An individual delay interval in delay intervals i₁through i_kmay be a duration of one or more bits, one or more bytes, one or more symbols, or any other suitable data length or combination of data lengths. An advantage of encoding using the scheme ofFIG. 29A is that all actual transmit time i₁can be as minimal as possible while the data encoding may extend a period of no transmission T₁. The average duty cycle of the transmitter emission may then fall substantially below 50%, which is a typical goal in most low power transmission systems. Since reasonable power is consumed when the transmitter is emitting, this encoding scheme is ultimately extremely power efficient from the standpoint of the transmitter.
• As shown inFIG. 29B, delaying a transmission of a second frequency channel ch_Bafter a transmission of a first frequency channel ch_Aby delay interval i₁may represent a first logic value, such as a binary zero-zero. A second logic value, such as a binary one-zero, may be represented by delaying the transmission of second frequency channel ch_Bafter the transmission of first frequency channel ch_Aby a combined duration of delay interval i₁through delay interval i₂. A third logic value, such as a binary one-one, may be represented by delaying the transmission of second frequency channel ch_Bafter the transmission of first frequency channel ch_Aby a combined duration of delay interval i₁through delay interval i₃. A fourth logic value, such as a binary zero-one, may be represented by delaying the transmission of second frequency channel ch_Bafter the transmission of first frequency channel ch_Aby a combined duration of delay interval i₁through delay interval i₄. However, this example is not limiting, those skilled in the arts will recognize that any logic value may be represented by delaying the transmission of second frequency channel ch_Bany number of delay intervals i₁through i_kwithout departing from the spirit and scope of the invention. For example, N logic values may be represented by delaying the transmission of second frequency channel ch_Bany suitable number of delay intervals i₁through i_Nand/or combinations thereof.
• In a particular embodiment, relevant to a low power and reasonablycompact sensor device104, a timing basis may be derived from a simple and non-accurate on-board clock. Simple, low power clocks tend to drift from a target frequency for a variety of reasons and conditions understandable to one of skill in the art. The drift is more severe the longer the time period from synchronization. An effective and efficient design for the embodiment ofFIG. 29B in this case may maintain a minimal time period i₁, while increasing the time periods i₂, i₃, and so on to compensate for anticipated maximal drift.
• A receiver, such asexternal computing device108 or one or moresensor link modules602 attached to the skin of the body, decodesacoustic communication signal2900 to recover the information signal. In particular, the receiver detects first frequency channel ch_Athen measures a length of the corresponding time delay T₁through T_Nuntil detection of second frequency channel ch_B. The receiver assigns a recovered logic value based upon the length of the corresponding time delay T₁through T_N. More specifically, the receiver measures the number of delay intervals i₁through i_kto determine the length of the corresponding time delay T₁through T_N, then assigns the logic value to a recovered information signal to recover the information signal based upon the length of the corresponding time delay T₁through T_N.
• To decodeacoustic communication signal2900 encoded according toFIG. 29B, the receiver assigns the first logic value to the recovered information signal when a time delay between first frequency channel ch_Aand second frequency channel ch_Bis measured as delay interval i₁. Likewise, if the receiver measures the time delay between first frequency channel ch_Aand second frequency channel ch_Bas the combined duration of delay interval i₁through delay interval i₂, the receiver assigns the second logic value to the recovered information signal. Similarly, if the receiver measures the time delay between first frequency channel ch_Aand second frequency channel ch_Bas the combined duration of delay interval i₁through delay interval i₃, the receiver assigns the third logic value to the recovered information signal. Finally, if the receiver measures the time delay between first frequency channel ch_Aand second frequency channel ch_Bas the combined duration of delay interval i₁through delay interval i₄, the receiver assigns the fourth logic value to the recovered information signal. However, this example is not limiting, those skilled in the arts will recognize that any logic value may be assigned to the recovered information signal based upon any suitable combination of delay intervals i₁through i_Kwithout departing from the spirit and scope of the invention. For example, N logic values may be assigned to the recovered information signal using any suitable number of delay intervals i₁through i_Kand/or combinations thereof.
• iii. Combination of Frequency Hopping and Differential Phase Shift Keying
• FIG. 30A illustrates a combined FH and differential phase shift keying (DPSK) scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention. From the discussion ofFIG. 27 above, a transmitter, such ascommunications module204, transmits anacoustic communication signal3000, such ascommunication signal106, by encoding an information signal, such assensor output signal212, onto frequency channels ch₁through ch_Ncorresponding to time intervals t₁, through t_N. The transmitter embeds one or more phases, denoted as φ₁through φ₁, of a corresponding carrier frequency, such as carrier frequencies f₁through f_Mas discussed inFIG. 28, onto each frequency channel in frequency channels ch₁through ch_Nto encode the information signal. In other words, transitions among one or more phases φ₁through φ₁within a corresponding frequency channel in frequency channels ch₁through ch_Nare used to encode the information signal.
• Phases φ₁through φ₁are relative to the preceding phase. Such systems, as would be expected in very low power devices such as withsensor device104, do not have extremely stable oscillators and may drift, have phase distortions, etc. Therefore, a phase reference to an initial phase, running for many bit periods and phase changes is very difficult to build. An encoding scheme that is simpler to implement in a low power scenario involving a phase change from a first time period t₁to a second time period t₂, another phase change from a time period t₂to a third time period t₃, and so on as is referred to herein as a differential phase change.FIG. 30B depicts two cycles of frequencies. Depending upon design goals and available bandwidths for operation, more or fewer cycles may be used as necessary as would be understood by a person skilled in the art. Thus, use of any number of cycles of frequencies in between phase changes does not depart from the spirit and scope of this invention.
• As shown inFIG. 30A, the transmitter transmits a carrier frequency having the one or more phases φ₁through φ₁such as one of carrier frequencies f₁through f_Mas shown inFIG. 28, associated with a first frequency channel, such as frequency channel ch₁, for a first interval of time, such as time interval t₁. The transmitter encodes the information signal by transmitting the one or more phases φ₁through φ₁of the carrier frequency throughout the first interval of time. After the first interval of time lapses or expires, the transmitter cycles through frequency channels ch₁through ch_Nas discussed inFIG. 27 and transmits the one or more phases φ₁through φ₁of the carrier frequency associated with frequency channels ch₁through ch_N, as discussed inFIG. 28 to encode the information signal.
• As shown inFIG. 30B, the transmitter transmits a first phase φ₁of a carrier frequency, such as carrier frequencies f₁through f_M, associated with frequency channels ch₁through ch_N, for a time interval t_A, a time interval t_B, and a time interval t_Cto represent a first logic value, such as a binary zero-zero. A combination of time interval t_A, time interval t_B, and time interval t_Cis substantially less than or equal to one or more of time intervals t₁, through t_N. A second logic value, such as a binary zero-one, may be represented by transmitting the first phase φ₁of the carrier frequency for time interval t_Aand time interval t_Bfollowed by transmitting a second phase φ₂of the carrier frequency for time interval t_c. A third logic value, such as a binary one-one, may be represented by transmitting the first phase φ₁of the carrier frequency for time interval t_A, the second phase φ₂of the carrier frequency for time interval t_B, followed by the first phase φ₁of the carrier frequency for time interval t_C. A fourth logic value, such as a binary one-zero, may be represented by transmitting the first phase φ₁of the carrier frequency for time interval t_A, the second phase φ₂of the carrier frequency for time interval t_Band time interval t_C. However, this example is not limiting, those skilled in the art will recognize that the transmitter may encode the information signal to represent any suitable number of logic values by transmitting at least one of the one or more phases φ₁through φ₁of the carrier frequency throughout time intervals t₁through t_N. For example, the transmitter may encode the information signal using a carrier frequency having four phase differences to generate a combined FH and differential quadrature phase shift keyed (DQPSK) acoustic communication signal, a carrier frequency having eight phase differences to generate a combined FH and differential 8-phase shift keyed (D8PSK) acoustic communication signal, and/or a carrier frequency having N phase differences to generate a combined FH and differential N-phase shift keyed (DNPSK) acoustic communication signal.
• A receiver, such asexternal computing device108 or one or moresensor link modules602 attached to the skin of the body, decodesacoustic communication signal3000 to recover the information signal. In particular, the receiver detects the one or more phases φ₁through φ₁of the carrier frequency throughout time intervals t₁through t_N. The receiver assigns a recovered logic value based upon a number of transitions among the one or more phases φ₁through φ₁of the carrier frequency.
• To decodeacoustic communication signal3000 encoded according toFIG. 30B, the receiver assigns the first logic value to the recovered information signal upon detecting the first phase φ₁of the carrier frequency for time interval t_A, time interval t_B, and time interval t_C. Likewise, if the receiver detects the first phase φ₁of the carrier frequency for time interval t_Aand time interval t_Bfollowed by the second phase φ₂of the carrier frequency for time interval t_C, the receiver assigns the second logic value to the recovered information signal. Similarly, if the receiver detects the first phase φ₁of the carrier frequency for time interval t_A, the second phase φ₂of the carrier frequency for time interval t_Bfollowed by the first phase φ₁of the carrier frequency for time interval t_C, the receiver assigns the third logic value to the recovered information signal. Finally, if the receiver detects the first phase φ₁of the carrier frequency for time interval t_Afollowed by the second phase φ₂of the carrier frequency for time interval t_Band time interval t_C, the receiver assigns the fourth logic value to the recovered information signal. However, this example is not limiting, those skilled in the art will recognize that the receiver may decode the acoustic communication signal by assigning any suitable number of logic values by detecting at least one of the one or more phases φ₁through φ₁of the carrier frequency throughout time intervals t₁, through t_N.
• FIG. 31 illustrates a block diagram of a transmitter to encode an information signal using a combined FH and DPSK scheme according to an exemplary embodiment of the present invention. Atransmitter3110 may be used to generateacoustic communication signal3000 as shown inFIG. 30A.Transmitter3110 may represent an exemplary embodiment ofcommunications module204. As will be understood by persons skilled in the relevant art from the teachings provided herein,transmitter3110 may be readily implemented in hardware, software, or a combination of hardware and software. For example, based on the teachings provided herein, a person skilled in the relevant art could implementtransmitter3110 via a combination of one or more application specific integrated circuits and a processor core for implementing software commands stored in one or more attached memories. However, this example is not limiting, and other implementations are within the scope and spirit of the present invention.
• As shown inFIG. 31,transmitter3110 may include anacoustic communications module3112 and aradiating element3114.Acoustic communications module3112 includes anencoder3100, afunction generator3102, amixer3104, and acarrier generator3106.Acoustic communications module3112 may represent an exemplary embodiment ofacoustic communications module302. Encoder3100 receives aninformation signal3150.Information signal3150 may include, but is not limited to,sensor output signal212. Encoder3100 encodesinformation signal3150 to generate areference pulse3154. In an exemplary embodiment,encoder3100partitions information signal3150 into one or more bits, one or more bytes, one or more symbols, or any other suitable manner that will be apparent to those skilled in the relevant art.
• Function generator3102 operates onreference pulse3154 to produce an encodedbaseband communication signal3156. More specifically,function generator3102 operates uponreference pulse3154 using one or more mathematical functions, such as a Walsh function or any other suitable mathematical function that will be apparent to those skilled in the relevant art. For example, for a one bit transmission,function generator3102 may store a first Walsh function S₁and a second Walsh function S₂. First Walsh function S₁may be represented as:
• 
  [S₀S₀],  (Eq. 6)
• where S₀is a reference pulse with any carrier frequency, such as carrier frequencies f₁through f_M. In an exemplary embodiment,reference pulse3154 represents reference pulse S₀. Likewise, second Walsh function S₂may be represented as:
• 
  [S₀−S₀].  (Eq. 7)
• Function generator3102 may output first Walsh function S_Ior second Walsh function S₂based uponreference pulse3154. However, this example is not limiting, those skilled in the art will recognize thatfunction generator3102 may operate uponreference pulse3154 using one or more mathematical functions without departing from the spirit and scope of the invention. For example, a set of Walsh functions for a two bit transmission may be denoted as S₁=[S₀S₀S₀S₀], S₂=[S₀S₀−S₀−S₀], S₃=[S₀−S₀−S₀S₀], and S₄=[S₀−S₀S₀−S₀]. Likewise, a set of Walsh functions for a three bit transmission may be denoted as S₁=[S₀S₀S₀S₀S₀S₀S₀S₀], S₂=[S₀S₀S₀−S₀−S₀−S₀−S₀-S₀], S₃=[S₀S₀−S₀−S₀−S₀−S₀S₀S₀], S₄=[S₀S₀−S₀−S₀S₀S₀−S₀−S₀], S₅=[S₀−S₀−S₀S₀S₀−S₀−S₀S₀], S₆=[S₀−S₀−S₀S₀−S₀S₀S₀−S₀], S₇=[S₀−S₀S₀−S₀−S₀S₀−S₀S₀], and S₈=[S₀−S₀S₀−S₀S₀−S₀S₀−S₀].
• Carrier generator3106 generates acarrier frequency3160 according to the FH scheme as discussed in conjunction withFIG. 27 andFIG. 28. For example,carrier generator3106 generatescarrier frequency3160 corresponding to carrier frequencies f₁through f_Massigned to frequency channels ch₁through ch_N.
• Multiplier3104 generates anelectrical communication signal3158 by multiplying encodedbaseband communication signal3156 andcarrier frequency3160. More specifically,multiplier3104 upconverts encodedbaseband communication signal3156 usingcarrier frequency3160 to generateelectrical communication signal3158.
• Radiating element3114 convertselectrical communication signal3158 to an acoustic representation to generate anacoustic communication signal3152.Acoustic communication signal3152 is an exemplary embodiment of, but is not limited to,communication signal106.Radiating element3114 may represent an exemplary embodiment of radiatingelement304.Radiating element3114 may be, but is not limited to, an electromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.) element or transducer that vibrates at acoustic frequencies.
• FIG. 32 illustrates a block diagram of a receiver to decode an acoustic communication signal using a combined FH and DPSK scheme according to an exemplary embodiment of the present invention. Areceiver3200, such asexternal computing device108 or one or moresensor link modules602 attached to the skin of the body, decodes anacoustic communication signal3250 to recover a recoveredinformation signal3252. As shown inFIG. 32,receiver3200 may include aradiating element3202, abandpass filter array3204, ademodulator3206, afunction generator3208, and acarrier generator3210.
• Radiating element3202 receivesacoustic communication signal3250, such asacoustic communication signal3000 to provide an example.Radiating element3202 convertsacoustic communication signal3250 to an electrical signal to generate anelectrical communication signal3254.Radiating element3202 may be, but is not limited to, an electromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.) element or transducer that vibrates at acoustic frequencies.
• Bandpass filter array3204 receiveselectrical communication signal3254 to generate a filteredcommunication signal3256.Bandpass filter array3204 may include a selectable arrangement of one or more bandpass filters. Each bandpass filter inbandpass filter array3204 may be implemented as, but not limited to, a Bessel filter, a Butterworth filter, a Chebyshev filter, a Comb filter, an Elliptic filter, or any other suitable filter topology to provide some examples. At least one or more of the bandpass filters corresponds to one or more of frequency channels ch₁through ch_N. In an exemplary embodiment,bandpass filter array3204 includes one bandpass filter for each of frequency channels ch₁through ch_N. For example, abandpass filter array3204 having five bandpass filters may filter an electrical representation ofacoustic communication signal3250, namelyelectrical communication signal3254, that is DPSK encoded over five frequency channels ch₁through ch₅.
• Demodulator3206 uses acarrier frequency3260 to demodulate and/or downconvert filteredcommunication signal3256 to produce ademodulated communication signal3258. In an exemplary embodiment,demodulator3206 demodulates filteredcommunication signal3256 to a baseband frequency.Demodulator3206 may be implemented as an optimal non-coherent demodulator, a suboptimal non-coherent demodulator, such as a delay-and-multiply receiver, or any other suitable demodulator capable of demodulating a DPSK, a DQPSK, a D8PSK, and/or a DNPSK encoded communication signal.
• Carrier generator3210 generatescarrier frequency3260 according to the FH scheme as discussed in conjunction withFIG. 27 andFIG. 28. For example,carrier generator3208 generatescarrier frequency3260 corresponding to carrier frequencies f₁through f_Massigned to frequency channels ch₁through ch_N.
• Function generator3208 receives demodulatedcommunication signal3258 to generate recoveredinformation signal3252, such ascommunication signal506 inFIG. 5.Function generator3208 generates recoveredinformation signal3252 by decoding demodulatedcommunication signal3258 using one or more mathematical functions, such as a Walsh function or any other suitable mathematical function to provide some examples. For example, for a one bit transmission,function generator3208 may operate upon demodulatedcommunication signal3258 using first Walsh function S₁and assign a first logic value to recoveredinformation signal3252 corresponding to first Walsh function S₁. Similarly,function generator3208 may operate upon demodulatedcommunication signal3258 using second Walsh function S₂and assign a second logic value to recoveredinformation signal3252 corresponding to second Walsh function S₂. Those skilled in the art will recognize thatfunction generator3208 may assign recoveredinformation signal3252 any suitable number and/or type of logic values using one or more suitable mathematical functions. For example,function generator3208 may assign recovered information signal3252 a first logic value, a second logic value, a third logic value and/or a fourth logic value corresponding to first Walsh function S₁, second Walsh function S₂, third Walsh function S₃, and/or fourth Walsh function S₄for a two bit transmission.
• In an exemplary embodiment,receiver3200 may simultaneously demodulate one or more acoustic communication signals3250.Receiver3200 may simultaneously receive one or moreacoustic communication signals3250 produced by one or more transmitters synchronously transmitting on a substantially identical frequency band using orthogonal sets of mathematical functions. For example, a first transmitter may use a first mathematical function, such as a first Walsh function S₁of [S₀S₀S₀S₀] and a second Walsh function S₂=[S₀S₀−S₀−S₀] for its bit transmission while a second transmitter may use a second mathematical function, such as a first Walsh function S₁of [S₀−S₀−S₀S₀] and a second Walsh function S₂=[S₀−S₀S₀−S₀] for its bit transmission.
• iv. Combination of Frequency Hopping and Frequency Shift Keying
• From the discussion ofFIG. 27 above, a transmitter, such ascommunications module204, may transmit an acoustic communication signal, such ascommunication signal106, by encoding an information signal, such assensor output signal212, onto frequency channels ch₁through ch_Ncorresponding to time intervals t₁, through t_N. The transmitter embeds one or more carrier frequencies, such as carrier frequencies f₁through f_M, onto each frequency channel in frequency channels ch₁through ch_Nto encode the information signal.
• FIG. 33A illustrates a hopping pattern used to encode and/or decode an acoustic communication signal using a combination of FH and differential frequency shift keying (DFSK) according to an exemplary embodiment of the present invention. Carrier frequencies f₁through f_Mas discussed inFIG. 28, may be partitioned or divided into one or more sets of carrier frequencies. The one or more sets of carrier frequencies may include one or more bands, registers, octaves, or any other suitable division of carrier frequencies f₁through f_Mthat will be apparent to those skilled in the art. For example, as shown inFIG. 33A, frequency channels ch₁through ch_Ncorrespond to a first set of carrier frequencies f including carrier frequencies f₁through f_M/2and a second set of carrier frequencies F including carrier frequencies f_M/2+1through f_M/2. However, this example is not limiting, those skilled in the arts will recognize that carrier frequencies f₁through f_Mmay be divided into one or more sets of carrier frequencies without departing from the spirit and scope of the invention. Those skilled in the arts will also recognize that the sets of carrier frequencies, such as first set of carrier frequencies f and second set of carrier frequencies F, may contain a similar and/or a dissimilar number of carrier frequencies and consecutive and/or non-consecutive frequencies without departing from the spirit and scope of the invention.
• Referring back toFIG. 33A, the transmitter and/or the receiver may assign one or more carrier frequencies to frequency channels ch₁through ch_N. For example, the transmitter and/or the receiver may assign carrier frequency f₁and/or carrier frequency f_M/2+1to frequency channel ch₁. Likewise, the transmitter and/or the receiver may assign carrier frequency f_M/2and/or carrier frequency f_Mto frequency channel ch₂. Similarly, the transmitter and/or the receiver may assign carrier frequency f₃and/or carrier frequency f_M/2+3to frequency channel ch₃. Finally, the transmitter and/or the receiver may assign carrier frequency f₃and/or carrier frequency f_M/2+3to frequency channel ch_N. However, this example is not limiting, those skilled in the arts will recognize that frequency channels ch₁through ch_Nmay be assigned to any other suitable sequence of carrier frequencies f₁through f_Mwithout departing from the spirit and scope of the invention. Furthermore, to ensure a frequency always has a clear channel, the frequencies can be assigned to the channels so that no frequency is used more than once.
• FIG. 33B further illustrates the hopping pattern used to encode and/or decode the acoustic communication signal using the combination of FH and DFSK according to an exemplary embodiment of the present invention. In this exemplary embodiment, carrier frequencies f₁through f_Mare partitioned or divided evenly into two sets of carrier frequencies. Carrier frequencies f₁through f_(M/2)form a first set of carrier frequencies f. Carrier frequencies f_(M/2+1)through f_Mform a second set of carrier frequencies F. In an exemplary embodiment, carrier frequencies f₁through f_(M/2)are substantially less than or equal to carrier frequencies f_(M/2+1)through f_M. However, this example is not limiting, those skilled in the arts will recognize that frequency channels ch₁through ch_Nmay be assigned to one or more sets of carrier frequencies using any other suitable sequence of carrier frequencies f₁through f_Mwithout departing from the spirit and scope of the invention.
• As shown inFIG. 33B, first set of carrier frequencies f may be stored in a first set of slots of a data register. Those skilled in the art will recognize that the functionality of the data register may be implemented using other suitable classes of storage media such as a volatile memory, for example a read-only memory (ROM), a non-volatile memory, such as a random access memory (RAM), or any other device capable of storing data without departing from the spirit and scope of the invention. Likewise, second set of carrier frequencies F may be stored in a second set of slots of the data register. The data register may be implemented as a processor register, a hardware register, or any other suitable category of storage area. In addition, the data register may be implemented as, but is not limited to, a general purpose register (GPR) to store both data and addresses, a floating point register (FPR) to store floating point numbers, a constant register to hold read-only values, a vector register to hold data for vector processing done by Single Instruction, Multiple Data (SIMD) instructions, a special function register, or any other suitable class of registers depending on the content of the data. The data register may be implemented as a register file, individual flip-flops, high speed core memory, thin film memory, and any other suitable implementation that will be apparent to those skilled in the art.
• The transmitter selects between first set of carrier frequencies f and second set of carrier frequencies F for each frequency channel in frequency channels ch₁through ch_Nto encode the information signal. In other words, transitions among first set of carrier frequencies f and second set of carrier frequencies F encode the information signal. As shown inFIG. 33C, the transmitter transmits a carrier frequency from first set of carrier frequencies f for a time interval t_AA, a time interval t_BB, and a time interval t_CCto represent a first logic value, such as a binary zero-zero. As used herein, the term “logic value” also refers to symbols belonging to sets of indeterminate size, not only to sets having just two states. Time interval t_AA, time interval t_BB, and time interval t_CCare substantially equal to a corresponding time interval t₁through t_Ncorresponding to frequency channels ch₁through ch_Nas discussed inFIG. 27. Alternately, the transmitter transmits a carrier frequency from second set of carrier frequencies F for a time interval t_AA, a time interval t_BB, and a time interval t_CCto represent the first logic value.
• A second logic value, such as a binary zero-one, may be represented by transmitting the carrier from first set of carrier frequencies f for time interval t_AAand time interval t_BBfollowed by the carrier frequency from second set of carrier frequencies F for time interval t_CC. Alternately, the second logic value may be represented by transmitting the carrier frequency from second set of carrier frequencies F for time interval t_AAand time interval t_BB, followed by the carrier frequency from first set of carrier frequencies f for time interval t_CC.
• A third logic value, such as a binary one-zero, may be represented by transmitting the carrier frequency from second set of carrier frequencies F for time interval t_AAand time interval t_BBfollowed by the carrier frequency from first set of carrier frequencies f for time interval t_CC. Alternately, the third logic value may be represented by transmitting the carrier frequency from first set of carrier frequencies f for time interval t_AAand time interval t_BB, followed by the carrier frequency from second set of carrier frequencies F for time interval t_CC.
• A fourth logic value, such as a binary one-one, may be represented by transmitting the carrier frequency from first set of carrier frequencies f for time interval t_AA, the carrier frequency from second set of carrier frequencies F for time interval t_BB, followed by the carrier frequency from first set of carrier frequencies f for time interval t_CC. Alternately, the fourth logic value may be represented by transmitting the carrier frequency from second set of carrier frequencies F for time interval t_AA, the carrier frequency from first set of carrier frequencies f for time interval t_BB, followed by the carrier frequency from second set of carrier frequencies F for time interval t_CC. However, this example is not limiting, those skilled in the art will recognize that the transmitter may encode the information signal to represent any suitable number of logic values by transmitting any suitable number of carrier frequencies from one or more sets of carrier frequencies without departing from the spirit and scope of the invention. For example, the transmitter may encode the information signal using four sets of carrier frequencies to generate a combined FH and differential quadrature frequency shift keyed (DQFSK) acoustic communication signal, eight sets of carrier frequencies to generate a combined FH and differential 8-frequency shift keyed (D8FSK) acoustic communication signal, and/or M sets of carrier frequencies to generate a combined FH and differential M-frequency shift keyed (DMFSK) acoustic communication signal.
• A receiver, such asexternal computing device108 or one or moresensor link modules602 attached to the skin of the body, decodes the acoustic communication signal to recover the information signal. In particular, the receiver detects the carrier frequency from first set of carrier frequencies f and/or the carrier frequency from second set of carrier frequencies F. The receiver compares a detected carrier frequency to a previously detected carrier frequency and assigns a recovered logic value based upon the similarity and/or difference between the detected carrier frequency and the previously detected carrier frequency. The receiver then assigns the recovered logic value to a recovered information signal to recover the information signal.
• To decode the acoustic communication signal encoded according toFIG. 33C, the receiver may assign the first logic value to the recovered information signal upon detecting the carrier frequency from first set of carrier frequencies f for time interval t_AA, time interval t_BB, and time interval t_CC. Alternately, the receiver may assign the first logic value to the recovered information signal upon detecting the carrier frequency from second set of carrier frequencies F for time interval t_AA, time interval t_BB, and time interval t_CC.
• The receiver may assign the second logic value to the recovered information signal upon detecting the carrier frequency from first set of carrier frequencies f for time interval t_AAand time interval t_BB, then detecting the carrier frequency from second set of carrier frequencies F for time interval t_CC. Alternately, the receiver may assign the second logic value to the recovered information signal upon detecting the carrier frequency from second set of carrier frequencies F for time interval t_AA, time interval t_BB, then detecting the carrier frequency from first set of carrier frequencies f for time interval t_CC.
• The receiver may assign the third logic value to the recovered information signal upon detecting the carrier frequency from second set of carrier frequencies F for time interval t_AAand time interval t_BB, then detecting the carrier frequency from first set of carrier frequencies f for time interval t_CC. Alternatively, the receiver may assign the third logic value to the recovered information signal upon detecting the carrier frequency from first set of carrier frequencies f for time interval t_AAand time interval t_BB, then detecting the carrier frequency from second set of carrier frequencies F for time interval t_CC.
• The receiver may assign the fourth logic value to the recovered information signal upon detecting the carrier frequency from first set of carrier frequencies f for time interval t_AA, the carrier frequency from second set of carrier frequencies F for time interval t_BB, then detecting the carrier frequency from first set of carrier frequencies f for time interval t_CC. Alternatively, the receiver may assign the fourth logic value to the recovered information signal upon detecting the carrier frequency from second set of carrier frequencies F for time interval t_AA, the carrier frequency from first set of carrier frequencies f for time interval t_BB, then detecting the carrier frequency from second set of carrier frequencies F for time interval t_CC. However, this example is not limiting, those skilled in the art will recognize that the receiver may decode the acoustic communication signal to represent any suitable number of logic values by detecting any suitable number of carrier frequencies from one or more sets of carrier frequencies without departing from the spirit and scope of the invention. For example, the receiver may decode the acoustic communication signal using four sets of carrier frequencies to decode the combined FH and DQFSK acoustic communication signal, eight sets of carrier frequencies to decode the combined FH and D8FSK acoustic communication signal, and/or M sets of carrier frequencies to decode the combined FH and DMFSK acoustic communication signal.
• v. Combination of Frequency Hopping and Differential Frequency Shift Keying, and Differential Phase Shift Keying
• FIG. 34A illustrates a combined FH, DFSK, and DPSK scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention. From the discussion ofFIG. 27 above, a transmitter, such ascommunications module204, transmits anacoustic communication signal3400, such ascommunication signal106, by encoding an information signal, such assensor output signal212, onto frequency channels ch₁through ch_Ncorresponding to time intervals t₁through t_N. From the discussion ofFIG. 33A, frequency channels ch₁through ch_Nmay be assigned to a first set of carrier frequencies f including carrier frequencies f₁through f_M/2and a second set of carrier frequencies F including carrier frequencies f_M/2+1through f_M/2. Referring back toFIG. 34A, the transmitter embeds one or more phases, denoted as φ₁through φ₁, of a corresponding carrier frequency from first set of carrier frequencies f and/or one or more phases φ₁through φ₁from second set of carrier frequencies F onto frequency channels ch₁through ch_Nto encode the information signal. The transmitter embeds one or more phases φ₁through φ₁corresponding to one or more sets of carrier frequencies onto each frequency channel in frequency channels ch₁through ch_Nto encode the information signal.
• As shown inFIGS. 34B and 34C, the transmitter transmits a first phase φ₁of a carrier frequency from first set of carrier frequencies f for a time interval t_Aand a time interval t_Bcorresponding to a time interval t_AA, and a time interval t_Aand a time interval t_Bcorresponding to a time interval t_BB to represent a first logic value, such as a binary zero-zero-zero. A combination of time interval t_Aand time interval t_Bis substantially less than or equal to corresponding time interval t_AAand/or corresponding time interval t_BB. Time interval t_AAand time interval t_BB is substantially less than or equal to corresponding time intervals t₁, through t_Nas discussed inFIG. 27.
• A second logic value, such as a binary zero-zero-one, may be represented by transmitting the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Aand time interval t_Bcorresponding to time interval t_AA, then the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Afollowed by asecond phase92 of the carrier frequency from first set of carrier frequencies f for time interval t_B, time interval t_Aand time interval t_Bcorresponding to time interval t_BB.
• A third logic value, such as a binary zero-one-one, may be represented by transmitting the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Aand time interval t_Bcorresponding to time interval t_AAthen afirst phase93 of the carrier frequency from second set of carrier frequencies F for time interval t_Afollowed by asecond phase94 of the carrier frequency from second set of carrier frequencies F for time interval t_B, time interval t_Aand time interval t_Bcorresponding to the time interval t_BB.
• A fourth logic value, such as binary zero-one-zero, may be represented by transmitting the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Aand time interval t_Bcorresponding to time interval t_AA, then thefirst phase93 of the carrier frequency from second set of carrier frequencies F for time interval t_Aand time interval t_Bcorresponding to time interval t_BB.
• A fifth logic value, such as binary one-zero-zero, may be represented by transmitting the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Afollowed by thesecond phase92 of the carrier frequency from first set of carrier frequencies f for time interval t_B, time interval t_Aand time interval t_Bcorresponding to time interval t_AA, then thesecond phase92 of the carrier frequency from first set of carrier frequencies f for time interval t_Aand time interval t_Bcorresponding to time interval t_BB.
• A sixth logic value, such as binary one-zero-one, may be represented by transmitting the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Afollowed by thesecond phase92 of the carrier frequency from first set of carrier frequencies f for time interval t_B, time interval t_Aand time interval t_Bcorresponding to time interval t_AA, then thesecond phase92 of the carrier frequency from first set of carrier frequencies f for time interval t_Afollowed by the by the second phase φ₂of the carrier frequency from first set of carrier frequencies f for time interval t_B, time interval t_Aand time interval t_Bcorresponding to time interval t_BB.
• A seventh logic value, such as binary one-one-one, may be represented by transmitting the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Afollowed by the second phase φ₂of the carrier frequency from first set of carrier frequencies f for time interval t_B, time interval t_Aand time interval t_Bcorresponding to time interval t_AA, then the first phase φ₃of the carrier frequency from second set of carrier frequencies F for time interval t_Afollowed by the second phase φ₄of the carrier frequency from second set of carrier frequencies F for time interval t_B, time interval t_Aand time interval t_Bcorresponding to time interval t_BB.
• An eighth logic value, such as binary one-one-zero, may be represented by transmitting the first phase φ₁of the carrier frequency from first set of carrier frequencies f for time interval t_Afollowed by the second phase φ₂of the carrier frequency from first set of carrier frequencies f for time interval t_B, time interval t_Aand time interval t_Bcorresponding to time interval t_AA, then the first phase φ₃of the carrier frequency from second set of carrier frequencies F for time interval t_Aand time interval t_Bcorresponding to time interval t_BB. However, this example is not limiting, those skilled in the art will recognize that the transmitter may encode the information signal to represent any suitable number of logic values by transmitting any suitable number of carrier frequencies from one or more sets of carrier frequencies where each carrier frequency includes one or more phase φ₁through φ₁without departing from the spirit and scope of the invention.
• FIG. 35 illustrates a block diagram of a transmitter to encode an information signal to a combination of FH, DFSK and DPSK acoustic communication signal according to an exemplary embodiment of the present invention. Atransmitter3500 may be used to generate anacoustic communication signal3552, such ascommunication signal3400 as shown inFIG. 34A, based on aninformation signal3550, such assensor output signal212.Transmitter3500 may represent an exemplary embodiment ofcommunications module204. As will be understood by persons skilled in the relevant art from the teachings provided herein,transmitter3500 may be readily implemented in hardware, software, or a combination of hardware and software. For example, based on the teachings provided herein, a person skilled in the relevant art could implementtransmitter3500 via a combination of one or more application specific integrated circuits and a processor core for implementing software commands stored in one or more attached memories. However, this example is not limiting, and other implementations are within the scope and spirit of the present invention.
• As shown inFIG. 35,transmitter3500 may include anacoustic communications module3502 and aradiating element3504.Acoustic communications module3502 includes abit splitter3504, a multiplier3506, a delay module3508, acarrier generator3510, aDFSK switch3512, aphase shifting module3514, and aDPSK switch3516.Acoustic communications module3502 may represent an exemplary embodiment ofacoustic communications module302.
• Bit splitter3504 receivesinformation signal3550.Bit splitter3504 parses or partitions theinformation signal3550 into afirst data stream3554A and asecond data stream3554B.Bit splitter3504 may partitioninformation signal3550 into one or more bits, one or more bytes, one or more symbols, or any other suitable manner that will be apparent to those skilled in the relevant art.First bit stream3554A andsecond bit stream3554B may be of similar or of dissimilar lengths.
• Amultiplier3506A comparesfirst data stream3554A to a first delayed DPSKswitch control signal3556A to produce a DPSKswitch control signal3558A. Afirst delay module3508A delays DPSKswitch control signal3558A by one or more bits, one or more bytes, one or more symbols, or any other suitable manner based upon a data length of the DPSKswitch control signal3558A to produce first delayed DPSKswitch control signal3556A. In an exemplary embodiment,first delay module3508A delays DPSKswitch control signal3558A by one bit. Likewise, amultiplier3506B multipliessecond data stream3554B and a second delayed encodeddata stream3556B to produce a second encodeddata stream3558B. Asecond delay module3508B delays second encodeddata stream3558B by one or more bits, one or more bytes, one or more symbols, or any other suitable manner based upon a data length of the second encodeddata stream3558B to produce second delayed encodeddata stream3558B. In an exemplary embodiment,second delay module3508B delays second encodeddata stream3558B by one bit.
• Thecarrier generator3510 generates afirst carrier frequency3562A from a first set of carrier frequencies and asecond carrier frequency3562B from a second set of carrier frequencies. More specifically,carrier generator3510 generates one or more carrier frequencies, such as carrier frequencies f₁through f_Mto provide an example, according to the FH scheme as discussed in conjunction withFIG. 27.Carrier generator3510 then divides the one or more carrier frequencies into the first set of carrier frequencies and the second set of carrier frequencies as discussed inFIG. 33A.
• TheDFSK switch3512 selects betweenfirst carrier frequency3562A andsecond carrier frequency3562B based upon second encodeddata stream3558B to generate aDFSK data stream3564. For example,DPSK switch3516 may selectfirst carrier frequency3562A when second encodeddata stream3558B corresponds to a first logical value, such as a binary zero to provide an example. Likewise,DPSK switch3516 may selectsecond carrier frequency3562B when second encodeddata stream3558B corresponds to a second logical value, such as a binary one to provide an example.
• Phase shifting module3514 alters a phase ofDFSK data stream3564 to produce a phase shiftedDFSK data stream3566. In an exemplary embodiment,phase shifting module3514 alters the phase ofDFSK data stream3564 by one hundred eighty degrees by invertingDFSK data stream3564.DPSK switch3516 selects betweenDFSK data stream3564 and phase shiftedDFSK data stream3566 based upon first encodeddata stream3558B to generate a combined DFSK and DPSK data stream3568. For example,DPSK switch3516 may select phase shiftedDFSK data stream3566 when DPSKswitch control signal3558A corresponds to a first logical value, such as a binary zero to provide an example. Likewise,DPSK switch3516 may selectDFSK data stream3564 when DPSKswitch control signal3558A corresponds to a second logical value, such as a binary one to provide an example.
• Radiating element3504 converts combined DFSK and DPSK data stream3568 to an acoustic representation to generateacoustic communication signal3552 based upon combined DFSK and DPSK data stream3568.Radiating element3504 may represent an exemplary embodiment of radiatingelement304.Radiating element3504 may be, but is not limited to, an electromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.) element or transducer that vibrates at acoustic frequencies.
• FIG. 36 illustrates a block diagram of a receiver to decode an information signal from an acoustic communication signal encoded using a combination of FH, DFSK and DPSK according to an exemplary embodiment of the present invention. Areceiver3600, such asexternal computing device108 or one or moresensor link modules602 attached to the skin of the body, decodes an acoustic communication signal3650 to recover aDFSK component3652 and aDPSK component3654. As shown inFIG. 36,receiver3600 may include aradiating element3602, acarrier generator3604, a DFSK/DPSK demodulator3606, aDPSK switch3608, and adifferential decoder3610.
• Radiating element3602 receives acoustic communication signal3650, such asacoustic communication signal3400 to provide an example.Radiating element3602 converts acoustic communication signal3650 to an electrical signal to generate anelectrical communication signal3656.Radiating element3602 may be, but is not limited to, an electromechanical transducer or piezoelectric (e.g., PZT, PVDF, etc.) element or transducer that vibrates at acoustic frequencies.
• Carrier generator3604 generates afirst carrier frequency3658A from a first set of carrier frequencies and asecond carrier frequency3658B from a second set of carrier frequencies. More specifically,carrier generator3604 generates one or more carrier frequencies, such as carrier frequencies f₁through f_Mto provide an example, according to the FH scheme as discussed in conjunction withFIG. 27.Carrier generator3604 then divides the one or more carrier frequencies into the first set of carrier frequencies and the second set of carrier frequencies as discussed inFIG. 33A.
• DFSK/DPSK demodulator3606 demodulateselectrical communication signal3656 using a corresponding carrier frequency to produce acorresponding DFSK output3660 and acorresponding DPSK output3662. More specifically, DFSK/DPSK demodulator3606A demodulateselectrical communication signal3656 usingfirst carrier frequency3658A from the first set of carrier frequencies to produce aDFSK output3660A and aDPSK output3662A. Likewise, DFSK/DPSK demodulator3606B demodulateselectrical communication signal3656 usingsecond carrier frequency3658B from the second set of carrier frequencies to produce aDFSK output3660B and aDPSK output3662B.
• FIG. 37 illustrates a block diagram of a demodulator to decode an information signal from an acoustic communication signal encoded using a combination of FH, DFSK, and DPSK according to an exemplary embodiment of the present invention. DFSK/DPSK demodulator3700 is an exemplary embodiment of DFSK/DPSK demodulator3606A and/or DFSK/DPSK demodulator3606B as shown inFIG. 36.
• Referring toFIG. 37, DFSK/DPSK demodulator3700 operates uponelectrical communication signal3656 using acorresponding carrier frequency3658 to produce acorresponding DFSK output3660 and acorresponding DPSK output3662. DFSK/DPSK demodulator3700 includes a multiplier3702, aphase shifter3704, an integrator3706, a multiplier3708, a delay module3710, asummation network3712, an in-phase correlator3714, an in-phase correlator3716, adecision device3718, aquadrature phase correlator3720, aquadrature phase correlator3722, and asummation network3724.
• Multiplier3702 downconvertselectrical communication signal3656 using a corresponding carrier frequency to produce a corresponding downconverted communication signal3752. More specifically, afirst multiplier3702A downconvertselectrical communication signal3656 usingcarrier frequency3658 to produce a firstdownconverted communication signal3752A. Likewise, asecond multiplier3702B downconvertselectrical communication signal3656 using a phase shiftedcarrier frequency3750 to produce a seconddownconverted communication signal3752B.Phase shifter3704 delays or shifts a phase ofcarrier frequency3658 to produce phase shiftedcarrier frequency3750. In an exemplary embodiment,phase shifter3704 shifts the phase ofcarrier frequency3658 by ninety degrees.
• Integrator3706 integrates a corresponding downconverted communication signal3752. More specifically,integrator3706A accumulates first downconvertedcommunication signal3752A within each half-symbol interval of T/2 to produce an in-phase information signal3754A. Likewise,integrator3706B accumulates second downconvertedcommunication signal3752B within each half-symbol interval of T/2 to produce a quadraturephase information signal3754B.
• Multiplier3708 multiplies in-phase information signal3754A and/or quadraturephase information signal3754B with a delayed in-phase information signal3756A and/or a delayed quadraturephase information signal3756B. More specifically,multiplier3708A multiplies in-phase information signal3754A with delayed in-phase information signal3756A to produce an in-phase decision statistic3758A.Delay module3710A delays in-phase information signal3754A by a half-symbol interval of T/2 to produce delayed in-phase information signal3756A. Likewise,multiplier3708B multiplies quadraturephase information signal3754B with delayed quadraturephase information signal3756B to produce a quadrature phase decision statistic3758B.Delay module3710B delays quadraturephase information signal3754B by a half-symbol interval of T/2 to produce delayed quadraturephase information signal3756B.
• Summation network3712 combines in-phase decision statistic3758A and in-phase decision statistic3758A to produce adecision statistic3760.Decision device3718 assigns a logic value toDPSK output3662 based upondecision statistic3760. In an exemplary embodiment,decision device3718 implements a signum function. For example, whendecision statistic3760 is less than zero,decision device3718 assigns a first bit estimate toDPSK output3662. Likewise, whendecision statistic3760 is greater than zero,decision device3718 assigns a second bit estimate toDPSK output3662.
• In-phase correlator3714 correlates in-phase information signal3754A to produce a correlated in-phase information signal3762A. Likewise, in-phase correlator3716 correlates delayed in-phase information signal3756A to produce a correlated delayed in-phase information signal3762B.Quadrature phase correlator3720 correlatesquadrature information signal3754B to produce a correlatedquadrature information signal3764A. Likewise,quadrature correlator3722 correlates delayedquadrature information signal3756B to produce a correlated delayed in-phase information signal3764B.Summation network3724 then combines correlated in-phase information signal3762A, correlated delayed in-phase information signal3762B, correlatedquadrature information signal3764A, and correlated delayed in-phase information signal3764B to produceDFSK output3660.
• FIG. 38 illustrates a block diagram of a demodulator to decode an information signal from an acoustic communication signal encoded using a combination of FH, DFSK, and DPSK according to another exemplary embodiment of the present invention. DFSK/DPSK demodulator3800 is an exemplary embodiment of DFSK/DPSK demodulator3606A and/or DFSK/DPSK demodulator3606B as shown inFIG. 36.
• Referring toFIG. 38, DFSK/DPSK demodulator3800 operates uponelectrical communication signal3656 using acorresponding carrier frequency3658 to produce acorresponding DFSK output3660 and acorresponding DPSK output3662. DFSK/DPSK demodulator3800 includes a multiplier3802, aphase shifter3804, an integrator3806, a multiplier3808, a delay module3810, a multiplier3812, asummation network3814, adifference network3816, adecision device3818, adecision device3820, abit combiner3822, an in-phase correlator3824, an in-phase correlator3826, aquadrature phase correlator3828, aquadrature phase correlator3830, and asummation network3832. Multiplier3802 downconvertselectrical communication signal3656 using a corresponding carrier frequency to produce a corresponding downconverted communication signal3852. More specifically, afirst multiplier3802A downconvertselectrical communication signal3656 usingcarrier frequency3658 to produce a firstdownconverted communication signal3852A. Likewise, asecond multiplier3802B downconvertselectrical communication signal3656 using a phase shiftedcarrier frequency3850 to produce a seconddownconverted communication signal3852B.Phase shifter3804 delays or shifts a phase ofcarrier frequency3658 to produce phase shiftedcarrier frequency3850. In an exemplary embodiment,phase shifter3804 shifts the phase ofcarrier frequency3658 by ninety degrees.
• Integrator3806 integrates a corresponding downconverted communication signal3852. More specifically,integrator3806A accumulates first downconvertedcommunication signal3852A within each half-symbol interval of T/2 to produce an in-phase information signal3854A. Likewise,integrator3806B accumulates second downconvertedcommunication signal3852B within each half-symbol interval of T/2 to produce a quadraturephase information signal3854B.
• Multiplier3808 multiplies in-phase information signal3854A and/or quadraturephase information signal3854B with a delayed in-phase information signal3856A and/or a delayed quadraturephase information signal3856B. More specifically,multiplier3808A multiplies in-phase information signal3854A with delayed in-phase information signal3856A to produce an in-phase decision statistic3858A.Delay module3810A delays in-phase information signal3854A by a half-symbol interval of T/2 to produce delayed in-phase information signal3856A. Likewise,multiplier3808B multiplies quadraturephase information signal3854B with delayed quadraturephase information signal3856B to produce a quadrature phase decision statistic3858B.Delay module3810B delays quadraturephase information signal3854B by a half-symbol interval of T/2 to produce delayed quadraturephase information signal3856B.
• Multiplier3828A multiplies in-phasephase information signal3854A with quadraturephase information signal3854B to produce a decision statistic3860A. Likewise, multiplier3828B multiplies in-phasephase information signal3854B with quadraturephase information signal3854B to produce a decision statistic3860B.
• Summation network3814 combines in-phase decision statistic3858A and in-phase decision statistic3858A to produce adecision statistic3862. Likewise,difference network3816 subtracts decision statistic3860A and decision statistic3860B to produce adecision statistic3864.Decision device3818 assigns a logic value to afirst DPSK output3866 based upondecision statistic3862. In an exemplary embodiment,decision device3818 implements a signum function. For example, whendecision statistic3862 is less than zero,decision device3818 assigns a first bit estimate tofirst DPSK output3866. Likewise, when decision statistic3860 is greater than zero,decision device3818 assigns a second bit estimate tofirst DPSK output3866. Similarly,decision device3820 assigns a logic value to asecond DPSK output3868 based upondecision statistic3862. In an exemplary embodiment,decision device3820 implements a signum function. For example, whendecision statistic3862 is less than zero,decision device3820 assigns a first bit estimate to thesecond DPSK output3868. Likewise, when decision statistic3860 is greater than zero,decision device3820 assigns a second bit estimate tosecond DPSK output3868.Bit combiner3822 combinesfirst DPSK output3868 andsecond DPSK output3868 to produceDPSK output3662A.
• In-phase correlator3824 correlates delayed in-phase information signal3856A to produce a correlated delayed in-phase information signal3870A. Likewise, in-phase correlator3826 correlates in-phase information signal3854A to produce a correlated in-phase information signal3870B.Quadrature phase correlator3828 correlatesquadrature information signal3854B to produce a correlatedquadrature information signal3872A. Likewise,quadrature correlator3830 correlates delayedquadrature information signal3856B to produce a correlated delayed in-phase information signal3872B.Summation network3832 then combines correlated in-phase information signal3870A, correlated delayed in-phase information signal3870B, correlatedquadrature information signal3872A, and correlated delayed in-phase information signal3872B to produceDFSK output3660.
• Referring back toFIG. 36,differential decoder3610 producesDFSK component3652 based uponDFSK output3660A andDFSK output3660B. In an exemplary embodiment,differential decoder3610 assigns a first logic value, such as a binary zero, toDFSK component3652 when the combination ofDFSK output3660A andDFSK output3660B is substantially equal to zero. Otherwise,differential decoder3610 assigns a second logic value, such as a binary one, toDFSK component3652 when the combination ofDFSK output3660A andDFSK output3660B is substantially equal to one. In addition,differential decoder3610 produces aDPSK selection signal3670.
• DPSK switch3608 selectsDPSK output3662A orDPSK output3662B based uponDPSK selection signal3670 to produceDPSK component3654. For example,DPSK switch3608 selectsDPSK output3662A whenDPSK selection signal3670 corresponds to a first logic value, such as a binary zero. Likewise,DPSK switch3608 selectsDPSK output3662B whenDPSK selection signal3670 corresponds to a second logic value, such as a binary one.
• vi. Use of Multiple Frequency Bands with a Combination of Frequency Hopping and Time Interval Encoding
• FIG. 39A illustrates a hopping pattern used to encode and/or decode an acoustic communication signal using multiple frequency bands with FH according to an exemplary embodiment of the present invention. As shown inFIG. 39A, an available bandwidth of the communication channel is substantially equally divided into three frequency bands B₁through B₃. For example, as shown inFIG. 39A, frequency band B₁includes a first bandwidth encompassing carrier frequencies f₁through f₁, frequency band B₂includes a second bandwidth encompassing carrier frequencies f_i+1through f_M−i−1, and frequency band B₃includes a third bandwidth encompassing carrier frequencies f_M−ithrough f_M. However, this example is not limiting, the available bandwidth of the communication channel may be divided into one or more frequency bands B₁through B_K. In addition, the available bandwidth of the communication channel need not be substantially equally divided into one or more frequency bands B₁through B_K. For example, frequency band B₁may encompass a greater amount of the available bandwidth of the communication channel when compared to frequency band B₂.
• In an embodiment utilizing substantially different frequency bands B₁and B₂, a received amplitude of a particular first frequency in band B₁as compared with a received amplitude of a particular second frequency in band B₂can derive distance from asensor device104 to a receiver such assensor link602. Acoustic attenuation of signals is proportional to a frequency of transmission for a given medium, such as withhuman body102. However, the knowledge of absolute amplitude of emission is not easily attainable for a reference to calculate a distance from a resulting attenuation. Considering multiple frequencies with multiple amplitudes, a sensitive receiver may be able to calculate with accuracy a difference between received amplitudes of these two frequencies. A mathematical model with known quantities of attenuation versus distance for both frequencies may then also solve a difference of known attenuations versus distances for both frequencies. In such an example, there is only one final solution that resolves the distance from a match of amplitude differentials with the difference in amplitude actually received. In so doing, use of a single phased array receiver (for the direction component of the location) in combination with use of multiple frequency bands (for the distance component of the location) can potentially resolve the location of the origin of acoustic signals to a reasonable accuracy.
• Referring back toFIG. 39A, a pulse P₁through P_Nmay be assigned a corresponding carrier frequency from one or more frequency bands B₁through B_K. For example, pulse P₁may be assigned to carrier frequency f₁from frequency band B₁, carrier frequency f_i+1from frequency band B₂, and/or carrier frequency f_M−ifrom frequency band B₃. However, this example is not limiting, those skilled in the arts will recognize that pulses P₁through P_Nmay be assigned to one or more frequency bands B₁through B_Kusing any other suitable sequence of carrier frequencies f₁through f_Mwithout departing from the spirit and scope of the invention. In an exemplary embodiment, one or more pulses P₁through P_Nare sequentially assigned to the carrier frequencies. After transmission and/or reception of pulse P₁using a carrier frequency from one of frequency bands B₁through B₃, a transmitter and/or a receiver sequentially reassigns the carrier frequency associated with the frequency band according to the hopping scheme. For example, if pulse P₁is transmitted and/or received using carrier frequency f₁associated with frequency band B₁, the transmitter and/or a receiver reassigns frequency band B₁to a next carrier frequency according to the hopping scheme and leaves frequency bands B₂and B₃in their current state.
• FIG. 39B illustrates a multiple frequency band with FH scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention. A transmitter, such ascommunications module204, transmits an acoustic communication signal, such ascommunication signal106, by encoding an information signal, such assensor output signal212, using one or more pulses P₁through P_Nas described inFIG. 39A.
• The transmitter selects one or more pulses P₁through P_Nfrom frequency bandwidths B₁through B₃to encode the information signal. As shown inFIG. 39B, the transmitter transmits a first pulse, such as pulse P₁, assigned to a carrier frequency from frequency band B₁for a time interval t_AAand a time interval t_BB followed by a third pulse, such as pulse P₃, assigned to a carrier frequency from frequency band B₃for time interval t_CCto represent a first logic value, such as a binary zero-zero. Time interval t_AA, time interval t_BB, and time interval t_CCare greater than or equal to a duration of a corresponding pulse in one or more pulses P₁through P_N. In an exemplary embodiment, third pulse P₃indicates an end of a transmission. However, this example is not limiting, those skilled in the arts will recognize that any one of pulses P₁through P_Nmay be used to indicate the end of the transmission without departing from the spirit and scope of the invention.
• A second logic value, such as a binary zero-one, may be represented by transmitting the first pulse assigned to the carrier frequency from frequency band B₁for time interval t_AA, a second pulse, such as pulse P₂, assigned to a carrier frequency from frequency band B₂for time interval t_BB, and third pulse P₃assigned to a carrier frequency from frequency band B₃for time interval t_CCto indicate the end of transmission.
• A third logic value, such as a binary one-one, may be represented by transmitting the pulse assigned to the carrier frequency from frequency band B₂for time interval t_AA and time interval t_BB, followed by the third pulse assigned to a carrier frequency from frequency band B₃for time interval t_CCto indicate the end of transmission.
• A fourth logic value, such as a binary one-zero, may be represented by transmitting the pulse assigned to the carrier frequency from frequency band B₂for time interval t_AA, a pulse assigned to the carrier frequency from frequency band B₁for time interval t_BB, followed by the third pulse assigned to the carrier frequency from frequency band B₃for time interval t_CC. However, this example is not limiting, any logic value may be represented by transmitting pulses P₁through P_Nassigned to carrier frequencies from frequency bands B₁through B_K. For example, a binary zero-zero-zero-one-zero-one-one-zero may be represented by transmitting the first pulse, the second pulse, and the third pulse assigned to a carrier frequency from frequency band B₁, a fourth pulse assigned to a carrier frequency from frequency band B₂, a fifth pulse assigned to a carrier frequency from frequency band B₁, a sixth and a seventh pulse assigned to a carrier frequency from frequency band B₂, and an eighth pulse assigned to a carrier frequency from frequency band B₁, followed by a ninth pulse assigned to a carrier frequency from frequency band B₃to indicate the end of transmission.
• A receiver, such asexternal computing device108 or one or moresensor link modules602 attached to the skin of the body, decodes the acoustic communication signal to recover the information signal. The receiver assigns the recovered logic value by detecting the carrier frequency from frequency band B₁, and/or the carrier frequency from frequency band B₂until the end of transmission as indicated by detecting the carrier frequency from frequency band B₃. In an exemplary embodiment, the receiver includes three detection circuits, one detection circuit for each frequency band B₁through B₃.
• To decode the acoustic communication signal encoded according toFIG. 39B, the receiver may assign the first logic value to a recovered information signal by detecting first pulse P₁assigned to the carrier frequency from frequency band B₁for a time interval t_AAand a time interval t_BB followed by third pulse P₃assigned to the carrier frequency from frequency band B₃for time interval t_CCto indicate the end of transmission.
• The receiver may assign the second logic value to the recovered information signal by detecting first pulse P₁assigned to the carrier frequency from frequency band B₁for time interval t_AA, second pulse P₂assigned to the carrier frequency from frequency band B₂for time interval t_BB, followed by third pulse P₃assigned to the carrier frequency from frequency band B₃for time interval t_CCto indicate the end of transmission.
• The receiver may assign the third logic value to the recovered information signal by detecting pulse P₂assigned to the carrier frequency from frequency band B₂for time interval t_AAand time interval t_BB, followed by third pulse P₃assigned to the carrier frequency from frequency band B₃for time interval t_CCto indicate the end of transmission.
• The receiver may assign the fourth logic value to the recovered information signal by detecting pulse P₂assigned to the carrier frequency from frequency band B₂for time interval t_AA, first pulse P₁assigned to the carrier frequency from frequency band B₁for time interval t_BB, followed by a third pulse P₃assigned to the carrier frequency from frequency band B₃for time interval t_CCto indicate the end of transmission. However, this example is not limiting, any logic value may be represented by transmitting pulses P₁through P_Nfor any suitable number of time intervals. For example, the receiver may assign a binary zero-zero-zero-one-zero-one-one-zero to the recovered information signal by detecting the first pulse, the second pulse, and the third pulse assigned to a carrier frequency from frequency band B₁, a fourth pulse assigned to a carrier frequency from frequency band B₂, a fifth pulse assigned to a carrier frequency from frequency band B₁, a sixth and a seventh pulse assigned to a carrier frequency from frequency band B₂, and an eighth pulse assigned to a carrier frequency from frequency band B₁followed by a ninth pulse assigned to a carrier frequency from frequency band B₃to indicate the end of transmission.
• FIG. 39C illustrates a multiple frequency band with FH and time interval encoding scheme to encode and/or decode an acoustic communication signal according to an exemplary embodiment of the present invention. As shown inFIG. 39C, a corresponding time delay T₁through T_Nhaving one or more time delay intervals, denoted as τ_N, may be used to implement a repeat function. The duration of time delay interval τ_Nis substantially less than or equal to the duration of a corresponding pulse in one or more pulses P₁through P_N. The repeat function indicates that the next bits of the acoustic communication signal are substantially equal to a previous bit transmitted and/or received based upon a number of time delay intervals τ_N. More specifically, delaying by a time delay interval τ_Nafter a binary one indicates that the next bits in the acoustic communication signal also indicate a binary one. Likewise, delaying by two time delay intervals τ_Nafter a binary one indicates that the two next bits in the acoustic communication signal also indicate a binary one. For example, the repeat function allows an eight bit word represented by binary zero-one-one-one-one-one-one-one to be encoded and/or decoded by transmitting and/or receiving a first pulse assigned to a carrier frequency from frequency band B₁, a second pulse assigned to a carrier frequency from frequency band B₂, and a period of five time delay intervals τ_N, followed by a third pulse assigned to a carrier frequency from frequency band B₃to indicate the end of transmission.
• The repeat function may also allow for the repetition of one or more bits, one or more bytes, one or more symbols, or any other suitable data length or combination of data lengths. For example, the repeat function may also allow the eight bit word represented by binary zero-one-one-one-one-one-one-one to be repeated n times by transmitting and/or receiving a first pulse assigned to a carrier frequency from frequency band B₁, a second pulse assigned to a carrier frequency from frequency band B₂, a period of five time delay intervals τ_N, a third pulse assigned to a carrier frequency from frequency band B₃, a period of n delay intervals τ_N, followed by a fourth pulse assigned to a carrier frequency from frequency band B₃to indicate the end of transmission.
• In another exemplary embodiment, the pulse assigned to a carrier frequency from frequency band B₃may be used to implement a truncation function. The truncation function indicates that the remaining bits of the acoustic communication signal are substantially equal to a previous bit transmitted and/or received. More specifically, truncating after a binary one indicates that the rest of the bits in the acoustic communication signal are also binary one. Likewise, truncating after a binary zero indicates that the rest of the bits in the acoustic communication signal are also binary zero. For example, the truncation function allows an eight bit word represented by binary zero-one-one-one-one-one-one-one to be encoded and/or decoded using substantially similar encoding and/or decoding as the second logic value as discussed above. In this example, third pulse P₃assigned to a carrier frequency from frequency band B₃indicates that the remaining six bits of the eight bit word are equal to a previous bit transmitted and/or received. Likewise, the truncation function allows an eight bit word represented by binary one-zero-zero-zero-zero-zero-zero-zero to be encoded and/or decoded using substantially similar encoding and/or decoding as the fourth logic value as discussed above. However, these examples are not limiting, the truncation function may be used to indicate that any suitable number of bits are substantially equal to the previous bit transmitted and/or received. In addition, the transmitter and/or the receiver may use the truncation function in any location throughout the encoding and/or decoding of the acoustic communication signal.
• In a further exemplary embodiment, the corresponding time delays T₁through T_N, including one or more time delay intervals τ_N, may be additionally used to encode the acoustic communication signal. In this exemplary embodiment, the transmitter transmits a first pulse assigned to a carrier frequency from one of the frequency bands, such as pulse P₁assigned to a carrier frequency from frequency band B₁, for a first interval of time, such as time interval t₁. The transmitter then waits or ceases to transmit for a corresponding time delay, such as time delay T₁, before beginning the transmission of a second pulse assigned to a carrier frequency from one of the frequency bands, such as pulse P₂including a carrier frequency from frequency band B₂. The transmitter encodes the information signal by varying a length of the corresponding time delay. More specifically, the transmitter encodes the information signal by delaying the transmission of the pulse by one or more time delay intervals τ_N. The one or more time delay intervals τ_Nwithin a corresponding time delay T₁through T_Nrepresent a logic value. The logic value may be one or more bits, one or more bytes, one or more symbols, or any other suitable data length or combination of data lengths. An individual delay interval in one or more time delay intervals τ_Nmay be a duration of one or more bits, one or more bytes, one or more symbols, or any other suitable data length or combination of data lengths so long as the duration of an individual delay interval τ_Nis substantially less than or equal to the duration of a corresponding pulse in one or more pulses P₁through P_N.
• In an additional exemplary embodiment, a pulse assigned to a carrier frequency from one of the frequency bands transmitted and/or received prior to one or more time delay intervals τ_Nmay be used to implement an advancement function. In other words, the pulse assigned to the carrier frequency from one of the frequency bands transmitted and/or received prior to one or more time delay intervals τ_Nmay correspond to a number of one or more time delay intervals τ_N. In other words, the transmitter and/or the receiver supplements a transmitted and/or a received one or more time delay intervals τ_Nwith a predetermined number of the one or more time delay intervals τ_N.
• As shown inFIG. 39D, a first pulse assigned to a carrier frequency from a first frequency band, such as pulse P₁assigned to a carrier frequency from frequency band B₁, may be assigned a value of zero delay intervals τ_N. Likewise, a second pulse assigned to a carrier frequency from a second frequency band, such as pulse P₂assigned to a carrier frequency from frequency band B₂, may be assigned a value of i delay intervals τ_N. Finally, a n^thpulse assigned to a carrier frequency from a n^thfrequency band, such as pulse P_Nassigned to a carrier frequency from frequency band B_N, may be assigned a value of j delay intervals τ_N. However, this example is not limiting, one or more pulses P₁through P_Nmay be assigned to any suitable value of delay intervals τ_Nwithout departing from the spirit and scope of the present invention.
• When encoding and/or decoding the acoustic communication signal, the transmitter and/or the receiver encodes and/or decodes the acoustic communication signal based upon an amount of one or more time delay intervals τ_Nincluded within the acoustic communication signal. On the other hand, the transmitter and/or the receiver supplements the transmitted and/or the received one or more time delay intervals τ_Nby factoring in an additional i delay intervals τ_Nwhen the pulse assigned to a carrier frequency from one of the frequency bands transmitted and/or received prior to one or more time delay intervals τ_Ncorresponds to the second pulse assigned to a carrier frequency from the second frequency band. In other words, transmitting and/or receiving the second pulse assigned to the carrier frequency from the second frequency band and waiting and/or measuring m time delay intervals τ_Nis substantially identical to waiting and/or measuring m+i time delay intervals τ_Nfor the purposes of encoding and/or decoding the acoustic communication signal. Likewise, the transmitter and/or the receiver supplements the transmitted and/or the received one or more time delay intervals τ_Nby factoring in an additional j delay intervals τ_Nwhen the pulse assigned to a carrier frequency from one of the frequency bands transmitted and/or received prior to the one or more time delay intervals τ_Ncorresponds to the n^thpulse assigned to a carrier frequency from the n^thfrequency band. In other words, transmitting and/or receiving the n^thpulse assigned to the carrier frequency from the second frequency band and waiting and/or measuring m time delay intervals τ_Nis substantially identical to waiting and/or measuring m+j time delay intervals τ_Nfor the purposes of encoding and/or decoding the acoustic communication signal.
VII. Conclusion
• While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. For example, acoustic data communication schemes can be conceived that combine all the techniques above. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims (17)

1. A method for communicating from an ingestible capsule, comprising:

modulating data from the ingestible capsule according to a modulation scheme;

spreading the modulated data according to a spreading code; and

acoustically transmitting the modulated and spread data through a body of an animal.

2. The method ofclaim 1, wherein the modulating comprises:

modulating data from the ingestible capsule according to a phase shift keying (PSK) modulation scheme.

3. The method ofclaim 2, wherein the modulating comprises:

modulating data from the ingestible capsule according to at least one of a binary PSK modulation scheme, a multi-level PSK modulation scheme, and a differential PSK modulation scheme.

4. The method ofclaim 2, wherein the modulating comprises:

modulating data from the ingestible capsule according to a first order differential PSK modulation scheme and a second order differential PSK modulation scheme.

5. The method ofclaim 1, wherein the spreading comprises:

spreading the modulated data according to a Barker spreading code.

6. The method ofclaim 1, further comprising:

receiving the acoustically transmitted signal;

de-spreading the received signal in accordance with the spreading code; and

demodulating the received and de-spread signal in accordance with the modulation scheme, wherein a phase of the spreading code is synchronized with the received signal whereby a signal-to-noise ratio of the received signal is increased.

7. The method ofclaim 1, further comprising:

receiving the acoustically transmitted signal;

multiplying the received signal by a plurality of spread signals to form a corresponding plurality of received spread signals;

demodulating the corresponding plurality of received spread signals in accordance with the modulation scheme; and

forming a final data signal from the plurality of demodulated signals, whereby a signal-to-noise ratio of the final data signal is increased.

8. The method ofclaim 7, wherein the forming comprising:

multiplying the plurality of demodulated signals by a corresponding plurality of signal-to-noise coefficients to form a plurality of weighted data signals; and

summing the plurality of weighted data signals to form the final data signal.

9. A system for communicating information, comprising:

an ingestible capsule comprising:

a modulator that modulates data according to a modulation scheme,

a spreader that spreads the modulated data according to a spreading code, and

an acoustic transmitter that acoustically transmits the modulated and spread data through a body of an animal.

10. The system ofclaim 9, wherein the modulator comprises a phase shift keying (PSK) modulator.

11. The system ofclaim 10, wherein the PSK modulator comprises at least one of a binary PSK modulator, a multi-level PSK modulator, and a differential PSK modulator.

12. The system ofclaim 10, wherein the PSK modulator comprises:

a first order differential PSK modulator that modulates a first finite differences of the data; and

a second order differential PSK modulator that modulates a second finite difference of the data.

13. The system ofclaim 9, wherein the spreader comprises a Barker spreading code generator.

14. The system ofclaim 13, wherein the Barker spreading code generator comprises a cyclic shift register.

15. The system ofclaim 9, further comprising:

a receiver comprising:

an acoustic transducer that receives the acoustically transmitted signal,

a de-spreader that de-spreads the received signal in accordance with the spreading code, and

a demodulator that demodulates the received and de-spread signal in accordance with the modulation scheme, wherein a phase of the spreading code is synchronized with the received signal whereby a signal-to-noise ratio of the received signal is increased.

16. The system ofclaim 9, further comprising:

a receiver comprising:

an acoustic transducer that receives the acoustically transmitted signal,

a plurality of spread signal generators that generate a corresponding plurality of spread signals,

a plurality of multipliers that multiplying the corresponding plurality of spread signals with the received signal to form a plurality of received spread signals,

a demodulator that demodulates the corresponding plurality of received spread signals in accordance with the modulation scheme; and

a decision-making module that forms a final data signal from the plurality of demodulated signals, whereby a signal-to-noise ratio of the final data signal is increased.

17. The system ofclaim 16, wherein the soft decision-making module comprises:

a plurality of signal-to-noise estimators that generate a corresponding plurality of signal-to-noise coefficients;

a plurality of multipliers that respectively multiply the plurality of demodulated signals and the plurality signal-to-noise coefficients to form a plurality of weighted data signals; and

a summation module that sums the plurality of weighted data signals to form the final data signal.

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