US20140049379A1 - Multiplexing radio frequency signals - Google Patents

Abstract

The present disclosure is directed to a system and method for multiplexing radio frequency signals. In some implementations, a system includes a host coupling module, a plurality of antennas, and a processing module. The host coupling module is configured to receive and transmit RF signals through a wired connection. The plurality of antennas are configured to wirelessly transmit RF signals and receive RF signals from RFID tags. The processing module is configured to selectively switch between the plurality of antennas for communication with the RFID tags using the host coupling module and backscatter at least a portion of the received RF signals through the wired connection to communicate information independent of an internal power supply.

Description

TECHNICAL FIELD
• This invention relates to multiplexing radio frequency signals and, more particularly, to multiplexing radio frequency signals for radio frequency identification (RFID).
BACKGROUND
• In some cases, an RFID reader operates in a dense reader environment, i.e., an area with many readers sharing fewer channels than the number of readers. Each RFID reader works to scan its interrogation zone for transponders, reading them when they are found. Because the transponder uses radar cross section (RCS) modulation to backscatter information to the readers, the RFID communications link can be very asymmetric. The readers typically transmit around 1 watt, while only about 0.1 milliwatt or less gets reflected back from the transponder. After propagation losses from the transponder to the reader the receive signal power at the reader can be 1 nanowatt for fully passive transponders, and as low as 1 picowatt for battery assisted transponders. At the same time other nearby readers also transmit 1 watt, sometimes on the same channel or nearby channels. Although the transponder backscatter signal is, in some cases, separated from the readers' transmission on a sub-carrier, the problem of filtering out unwanted adjacent reader transmissions is very difficult.
SUMMARY
• The present disclosure is directed to a system and method for multiplexing radio frequency signals. In some implementations, a system includes a host coupling module, a plurality of antennas, and a processing module. The host coupling module is configured to receive and transmit RF signals through a wired connection. The plurality of antennas are configured to wirelessly transmit RF signals and receive RF signals from RFID tags. The processing module is configured to selectively switch between the plurality of antennas for communication with the RFID tags using the host coupling module and backscatter at least a portion of the received RF signals through the wired connection to communicate information independent of an internal power supply.
DESCRIPTION OF THE DRAWINGS
• FIGS. 1A and 1B are block diagrams illustrating example interrogation systems in accordance with some implementations of the present disclosure;
• FIG. 2 is a block diagram illustrating an example RFID multiplexer ofFIGS. 1A and 1B in accordance with some implementations of the present disclosure;
• FIG. 3 is a flow chart illustrating an example method for using an RFID multiplexer ofFIGS. 1A and 1B;
• Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTION
• FIGS. 1A and 1B are block diagrams illustrating anexample system100aand100b,respectively, for multiplexing Radio Frequency (RF) signals in accordance with some implementations to the present disclosure. For example, the system100 may selectively switch communications between a plurality of antennas based, at least in part, on communications received through a wired connection. In some implementations, the system100 may multiplex RF signals based, at least in part, on signals received through a single wired connection. In some implementations, the system100 may operate using power based on RF signals received through a single wired connection. In general, the system100 may perform one or more of the following: receive RF signals through a single wired connection (e.g., commands, signals for RFID tags); selectively switch between antennas for communicating with RFID tags; backscatter RF signals received through a wired connection to transmit information (e.g., response, status information) to a host RF transceiver; operate elements based on power from RF signals received through a single wired connection to a host RF transceiver; forward received RF signals to a second multiplexing device through a wired connection; and/or others. In operating the system100 in accordance with some of these implementations, the system100 may provide one or more of the following advantages: a single control line (e.g., a coaxial cable or another type of transmission line) that to multiplex RF signals and/or power at least a portion of a multiplexer; an RFID multiplexer may be located at any point between an RFID host and antennas, minimizing or otherwise reducing installation and/or infrastructure costs; transmitting wired communications to a host RF transceiver using power from RF signals received through the same wired connection; and/or other advantages.
• Referring toFIG. 1A, theRFID system100aincludes, at a high level, RFID tags104a-fcommunicably coupled to ahost RF transceiver102. Thetags104d-fare communicably coupled to thehost transceiver102 through anRFID multiplexer108. For example, thehost transceiver102 may wirelessly communicate with theRFID tags104d-fusing theRFID multiplexer108. In some implementations, theRFID multiplexer108 can receive RF signals from thehost transceiver102 and transmit at least a portion of the received RF signals to thetags104d-fusing one ormore antennas110. TheRFID multiplexer108 may demodulate at least a portion of the received RF signals to baseband frequency signals that control one or more aspects of operation of theRFID multiplexer108. For example, theRFID multiplexer108 may selectively switch between theantennas110 to transmit signals to thetags104d-fbased, at least in part, on the baseband frequency signals. In some implementations, theRF multiplexer108 can backscatter at least a portion of the received RF signals to theRFID host102. In this case, theRF multiplexer108 may communication information to theRFID host102 such as status information (e.g., power level) as well as other information. Other information may include identification of a current antenna selection, firmware configuration values, locally stored data, an address and/or identification of thespecific RF multiplexer108, version information for theRF multiplexer108, version information for a component of theRF multiplexer108, temperature information, measured incident RF power seen from the host (which may be used, for example, to account for cable losses), and/or other information. In communicating with thehost transceiver102, theRFID multiplexer108 may emulate an RFID tag such that at least some information is transmitted to thehost102 in accordance with an RFID protocol. In some implementations, theRFID multiplexer108 can use at least a portion of the received RF signals to power one or more components of theRFID multiplexer108. For example, theRFID multiplexer108 may rectify a portion of the received RF signals to DC signals and use the DC signals to power an internal components (e.g., logic). Such elements may include a DC power tap module, a controller module, a DC power jack, transmission modules, a communication module and/or others.
• Turning to a more detailed description of thesystem100a,theRFID multiplexer108 can include any software, hardware, and/or firmware configured to multiplex RF signals. For example, themultiplexer108 may selectively switch between theantennas110 to communicate with thetags104d-findependent of an internal power supply such as a battery. In some implementations, theRFID multiplexer108 include a plurality ofmodules112a-#. For example, theRFID multiplexer108 may include ahost coupling module112aand acommunication module112b,and thecommunication module112amay communicates with theRFID host102 through thehost coupling module112ausing a wired connection114. For example, thehost coupling module112amay be a coaxial cable port such that theRFID host102 may be directly connected to theRFID multiplexer108 by a coaxial cable114. Thecommunication module112bmay receive RF signals from theRFID host102 and downconvert the RF signals to baseband frequency signals. Baseband frequency signals may include low frequency signals, e.g., near zero frequency. The baseband frequency signals may include information for controlling one or more aspects of multiplexer operation. For example, the baseband frequency signals may identify one or more of theantennas110 connected to theRFID multiplexer108. In this case, themultiplexer108 may selectively switch between theantennas110 in accordance with the identifying information. In operating at least a portion of theRFID multiplexer108, the system may provide one or more of the following advantages over alternative systems: a single control line (e.g., a coaxial cable or another type of transmission line) may transfer signals from theRFID host102 to theRFID multiplexer108 to operate and power theRFID multiplexer108 and to communicate with tags104; theRFID multiplexer108 may be located at any point between theRFID host102 andantennas110, reducing and/or minimizing installation and infrastructure costs; theRFID multiplexer108 may send reply signals to theRFID host102 using power received at least in part from theRFID host102.
• In some implementations, theRFID multiplexer108 includes aswitching module112cand acontroller module112dsuch that thecontrol modules112dcontrols theswitching module112cbased, at least in part, on the signals received from theRFID host102. For example, theswitching module112cmay selectively couple one ormore antennas110 to thehost coupling module112afor wireless communication between thehost102 and thetags104d-f.In some implementations, theRFID multiplexer108 can act as a port extension for communication between thehost102 and one or more RF tags104. Thecommunication module112bmay rectify a portion of the RF signals received from theRFID host102 to DC power signals. The power signals may provide power to one or more components of theRFID multiplexer108. For example, thecommunication module112bmay convert 910 MHz signals to low frequency (e.g., 0 Hz) power signals for powering one or more modules or components of theRFID multiplexer108. Thecommunication module112bmay measure an amount of power received by theRFID multiplexer108 from theRFID host102. For example, signal losses along the control line114 may reduce the amount of power received by theRFID multiplexer108 from theRFID host102. TheRFID multiplexer108 may communicate to theRFID host102 information identifying an amount of measured power received from theRFID host102, and theRFID host102 may compensate for power losses by increasing an amount of power transmitted from theRFID host102 to theRFID multiplexer108. For example, theRFID multiplexer108 may serve as a port extension to compensate for line losses and/or deliver an increased amount of RF signal power to one or more of theantennas110 while remaining within regulatory and/or desired output power criteria.
• Thecommunication module112bmay backscatter a portion of the RF signals received from theRFID host102. For example, thecommunication module112bmay include one or more tag emulator modules116 that are analogous to a passive tag operating in the field of theRFID host102. The tag emulator module116 may transmit a reply to a received signal from theRFID host102 using power stored from the previously received RF signals, independent of an internal power source. Thecommunication module112bmay modulate a response signal onto the backscattered RF signal, for example, by modulating the radio cross section of thecommunication module112b.The response signal may include information related to the measured amount of power received by theRFID multiplexer108. TheRFID host102 may receive the backscattered signal. In the previous example, theRFID host102 may receive the backscattered signal, and based at least in part on the response signal included in the backscattered signal, theRFID host102 may increase or decrease an amount of power transmitted to theRFID multiplexer108.
• In some implementations where theRFID multiplexer108 includes acontrol module112d,thecontrol module112dmay convert an analog baseband frequency signal to a digital baseband frequency signal. Thecontrol module112dmay implement one or more operations based at least in part on the digital baseband frequency signals. For example, thecontrol module112dmay include a processor that controls coupling between thehost coupling module112aandantennas110. Thecontrol module112dmay also convert digital signals to analog signals. For example, thecontrol module112dmay convert a digital baseband frequency digital signal to an analog baseband frequency signal, and the analog baseband frequency signal may include information to be communicated to theRFID host102. In some cases, the analog baseband frequency signal generated by the control module is modulated and transmitted to theRFID host102 in a backscattered RF signal.
• TheRFID multiplexer108 may include apower tap module112eto detect a DC signal component of an RF signal received from theRFID host102. In some implementations, thepower tap module112ecan be coupled to thehost coupling module112aof theRFID multiplexer108. TheRFID multiplexer108 may receive from theRFID host102 an RF signal that includes a DC power component, and thepower tap module112emay detect the DC power signal component and output the detected DC power signal component to provide power to an internal or external system (e.g., thecontrol module112d). While the DC component provides power, for example, to thecontrol module112d,one or more of theantennas110 may simultaneously transmit a different portion (i.e., a non-DC component) of the received RF signals. For example, thepower tap module112emay pass RF signal components to one ormore antennas110 for transmission to thetags104d-f.
• In some implementations, theRFID multiplexer108 can include aDC power module112fto provide power to theRFID multiplexer108. For example, theDC power module112fmay include a battery or a wall jack with an AC to DC converter. The DC power module may provide power to thecontroller module112dand/or or to another components112 of theRFID multiplexer108. In some implementations, theDC power module112fcan provide power to theRFID multiplexer108 to supplement power received by theRFID multiplexer108 from theRFID host102.
• TheRFID host102 includes any software, hardware, and/or firmware configured to transmit and receive RF signals. In general, theRFID host102 may transmit requests for information within a certain geographic area associated withRFID host102. TheRFID host102 may transmit the query in response to a request, automatically, in response to a threshold being satisfied (e.g., expiration of time), as well as others. The interrogation zones106 may be based on one or more parameters such as transmission power, associated protocol (i.e. set of rules for communication between RFID tags and readers), nearby impediments (e.g. objects, walls, buildings), as well as others. In general, theRFID host102 may include a controller, a transceiver coupled to the controller, and one ormore RF antennas110 coupled to the transceiver. One ormore RF multiplexers108 may be coupled to the transceiver. For example, thetransceiver102 may be directly connected to themultiplexer108 through a wired connection114. In some implementations, theRFID multiplexer108 can act as a port extension for theRFID host102. In some examples, theRF antennas110 connected to thehost102 and theRF antennas110 connected to theRFID multiplexer108 may transmit requests and receive responses from RFID tags104 in the associated interrogation zones106. In some implementations, theRFID host102 can determine statistical data based, at least in part, on tag responses. TheRFID host102 often includes a power supply or may obtain power from a coupled source for powering included elements and transmitting signals. In general, theRFID host102 and theRFID multiplexer108 operate in one or more specific frequency bands allotted for RF communication. For example, the Federal Communication Commission (FCC) has assigned 902-928 MHz and 2400-2483.5 MHz as frequency bands for certain RFID applications. In some implementations theRFID host102 and/or theRFID multiplexer108 can dynamically switch between different frequency bands and/or protocols.
• The RFID tags104 can include any software, hardware, and/or firmware configured to respond to communication from theRFID host102 and/or from theRFID multiplexer108. These tags104 may operate without the use of an internal power supply. Rather, the tags104 may transmit a reply using power stored from the previously received RF signals, independent of an internal power source. This mode of operation is typically referred to as backscattering. In some implementations, the tags104 alternate between absorbing power from signals transmitted by theRFID host102 and transmitting responses to the signals using at least a portion of the absorbed power. In passive tag operation, the tags104 typically have a maximum allowable time to maintain at least a minimum DC voltage level. In some implementations, this time duration is determined by the amount of power available from an antenna of a tag104 minus the power consumed by the tag104 and the size of the on-chip capacitance. The effective capacitance can, in some implementations, be configured to store sufficient power to support the internal DC voltage when there is no received RF power available via the antenna. The tag104 may consume the stored power when information is either transmitted to the tag104 or the tag104 responds to the RFID host102 (e.g., modulated signal on the antenna input). In transmitting responses back to theRFID host102, the tags104 may include one or more of the following: an identification string, locally stored data, tag status, internal temperature, and/or others.
• In one aspect of operation, theRFID host102, using theRFID multiplexer108, periodically transmit signals to the interrogation zones106. For example, theRFID host102 may transmit RF signals to theinterrogation zone106bby transmitting RF signals to theRFID multiplexer108 using the wired connection114. TheRFID multiplexer108 may wirelessly transmit at least a portion of the received RF signals received through the wired connection114 to theinterrogation zone106b.In the event that a tag104 is within one of the interrogation zones106, the tag104 may transmit a response. For example, thetags104d-fin theinterrogation zone106bmay transmit a response to theRFID multiplexer108, and theRFID multiplexer108 may then send the received response to theRFID host102. As another example, the tags104a-cin theinterrogation zone106amay transmit a response to theRFID host102.
• In another aspect of operation, theRFID host102 communicates with theRFID multiplexer108. For example, theRFID host102 may send to theRFID multiplexer108 instructions to select one or more of theantennas110 for wirelessly transmitting signals to theinterrogation zone106b.In this example, themultiplexer108 may select one of theantennas110 and pass the identified signal to theantenna110 for transmission in the interrogation some106b.In some implementations, theRFID multiplexer108 may backscatter RF signals to theRFID host102. For example, theRFID multiplexer108 may the backscattered RF signal to transmit a response signal indicating an amount of power received from theRFID host102. The response signal may include other information related to operation of theRFID multiplexer108. For example, the response signal may include information identifying an amount of power received from an external DC power source, anantenna110 used to transmit RF signals, an ambient temperature and/or other operating conditions. TheRFID host102 may receive the backscattered RF signal. In response to the backscattered RF signal, theRFID host102 may, for example, increase or decrease an amount of transmitted RF power. In some cases, theRFID host102 responds by sending another RF signal to theRFID multiplexer108 instructing theRFID multiplexer108 to switch to adifferent antenna110.
• Referring toFIG. 1B, thesystem100bincludes a plurality ofRF multiplexers108aand108bbimplemented in a series configuration from asingle RFID host102. TheRFID host102 may communicate with thetags104gand104hin theinterrogation zone106cand/or with theRFID multiplexer108a.TheRFID multiplexer108amay receive RF signals from theRFID host102. TheRFID multiplexer108amay backscatter at least a portion of the received RF signals to theRFID host102. TheRFID multiplexer108amay use one ormore antennas110 to wirelessly transmit at least a portion of the received RF signals. For example, theRFID multiplexer108amay communicate wirelessly with the tags104iand104jin theinterrogation zone106d.TheRFID multiplexer108amay receive RF signals from one or more tags104 and transmit the received RF signals to theRFID host102. TheRFID multiplexer108amay also communicate with theRFID multiplexer108b.TheRFID multiplexer108bmay receive RF signals from theRFID multiplexer108a.TheRFID multiplexer108bmay backscatter at least a portion of the received RF signals to theRFID multiplexer108a.TheRFID multiplexer108bmay use one ormore antennas110 to wirelessly transmit at least a portion of the received RF signals. For example, theRFID multiplexer108bmay communicate wirelessly with thetags104k,104lin the interrogation zone106e.TheRFID multiplexer108bmay receive RF signals from one or more tags104 and re-transmit the received RF signals to theRFID multiplexer108a.TheRFID multiplexer108amay, in turn, re-transmit the received RF signals to theRFID host102. TheRFID multiplexer108bmay communicate to theRFID multiplexer108aan identification of an amount of measured power received from theRFID multiplexer108a.
• FIG. 2 illustrates anexample RFID multiplexer108 ofFIGS. 1A and 1B in accordance with some implementations of the present disclosure. In particular, the illustratedmultiplexer108 includes a port202, acommunication module204, acontrol module206, and aswitching module208. In some implementations, theRFID multiplexer108 includes apower tap module210 and aDC power module214. The communication module may be coupled to the port202 through adirectional coupler212. Theswitching module208 may selectively connect the port202 to one ormore antennas110, to anotherRFID multiplexer108, and/or to another device. TheRF multiplexer108 may include some, all, additional, or different elements without departing from the scope of this disclosure. For example, theRFID multiplexer108 may include memory, capacitors, and/or other components. Theexample RFID multiplexer108 and its various components are illustrated schematically, and a typical implementation may include components and/or connections not illustrated in the diagram illustrated inFIG. 2.
• The port202 couples theRFID multiplexer108 to an RFID host102 (not illustrated), for example, through a single wired connection such as a coaxial cable. The port202 may receive RF signals from theRFID host102 and send at least a portion of the received RF signals to thepower tap module210, thecommunication module204, and/or theswitching module208. In some implementations, thepower tap module210 is omitted, and at least a portion of the received RF signals are sent directly to thecommunication module204 and/or theswitching module208. Signals may also be transmitted back to theRFID host102 from theRFID multiplexer108 through the port202. For example, thecommunication module204 may backscatter RF signals to theRFID host102 through the port202. As another example, one or more of theantennas110 may wirelessly receive signals from tags104, and the received signal may be sent to theRFID host102 through the port202.
• Thecommunication module204 can include any software, hardware, and/or firmware configured to communicate with theRFID host102. As illustrated, thecommunication module204 may be implemented with areceiver module216 and atag emulator module218. However, in other implementations, thereceiver module216 and thetag emulator module218 can be implemented in a different configuration, for example, as a single module. Thecontrol module206 and/or its constituent components may include or have access to one or more amplifiers (e.g., power amplifiers), one or more filtering mechanisms (e.g., low pass filters, high pass filters, band pass filters, band stop filters, and/or others), one or more fixed-frequency oscillators (e.g., a reference or clock signal), and/or other components.
• At a high level, thecommunication module204 may receive signals from theRFID host102, and based at least in part on the received RF signals, thecommunication module204 may provide baseband frequency signals to thecontrol module206, backscatter RF signals to theRFID host102, and/or provide power to one or more components of theRFID multiplexer108. The baseband signals may include instructions for operating one or more aspects of theRFID multiplexer108, such as for controlling theswitching module208. In some implementations, thecommunication module204 selectively switches between a backscattering mode and a transmission mode. For example, thecommunication module204 may receive a backscatter control signal from thecontrol module206. The backscatter control signal may control a switch in thecommunication module204 that activates the backscattering mode of thecommunication module204.
• In some implementations, thereceiver module216 and thetag emulator module218 are coupled to the port202 and/or to each other. Thereceiver module216 and thetag emulator module218 may be connected to the port202 either directly or indirectly through another component of theRFID multiplexer108, such as thedirectional coupler212 and/or thepower tap module210. In some implementations, thereceiver module216 and thetag emulator module218 are coupled directly and/or indirectly to thecontrol module206.
• Thereceiver module216 may receive an RF signal from theRFID host102 through the port202 and/or through a different connection. Thereceiver module216 may detect an amount of power received from theRFID host102. For example, thereceiver module216 may detect 1 milliwatt (mW) of power received from theRFID host102. Thereceiver module216 may communicate to thecontrol module206, or to a different device, the measured amount of power. In the example, thereceiver module216 communicates to thecontrol module206 that 1 mW of power is received from theRFID host102. In some implementations, theRFID multiplexer108 communicates the measured amount of received power to theRFID host102. For example, the measured amount of received power may be identified in a signal backscattered from thetag emulator module218 to theRFID host102.
• Thereceiver module216 may convert at least a portion of the received RF signals to power signals. In this manner, thereceiver module216 may provide power to one or more components of theRFID multiplexer108 based, at least in part, on the received RF signals. In some implementations, thereceiver module216 may includes rectify a portion of the received RF signals to DC power signals, and the DC power signals may provide power to thecontrol module206 and/or other components of theRFID multiplexer108.
• Thereceiver module216 may demodulate at least a portion of the received RF signals to baseband frequency signals. For example, thereceiver module216 may receive a signal having a 910 MHz carrier signal and demodulate the carrier signal out of the received signal to produce a lower frequency baseband signal. The baseband signal may include data or instructions for controlling one or more aspects of operation of theRFID multiplexer108. For example, the baseband signal may be converted to a digital baseband signal by thecontrol module206, and based on the digital baseband signal, thecontrol module206 may send instructions to theswitching module208 to selectively switch one or more of theantennas110 to the port202.
• Thetag emulator module218 may backscatter RF signals received from theRFID host102. For example, thetag emulator module218 may implement one or more RFID communication protocols. In this regard, thetag emulator module218 may operate similarly to a tag104. However, thetag emulator module218, in some implementations, communicates by a wired connection to theRFID host102, rather than wirelessly, as the tags104. For example, thetag emulator module218 may backscatter RF signals through the port202 and along a coaxial cable connection to theRFID host102. Thetag emulator module218 may be configured to respond to communication from theRFID host102. Thetag emulator module218 may operate without the use of an internal power supply. Rather, thetag emulator module218 may transmit a reply to a received signal from theRFID host102 using power stored from the previously received RF signals, independent of an internal power source. In transmitting responses back to theRFID host102, the tags104 may include one or more of the following: an amount of power received from theRFID host102, an amount of power received from an external or internal power supply, an identification string, locally stored data, tag status, internal temperature, and/or other information.
• Thetag emulator module218 may include anysuitable switching mechanism220 for activating and/or deactivating a backscatter mode. For example, thetag emulator module218 may receive a signal from thecontrol module206 that controls the switching mechanism of thetag emulator module218. Theswitching mechanism220 may effectively control an impedance of thetag emulator module218. For example, when the backscatter mode is activated, thetag emulator module218 may have a high effective impedance, and when the backscatter mode is deactivated, thetag emulator module218 may have a low effective impedance (e.g., 50 ohms).
• Thecontrol module206 can include any software, hardware, and/or firmware configured to select one or more transmission modules to transmit signals received from an RF host. Thecontrol module206 may include or have access to one or more amplifiers (e.g., power amplifiers), a digital to analog converter (DAC), an analog to digital converter (ADC), one or more filtering mechanisms (e.g., low pass filters, high pass filters, band pass filters, band stop filters, and/or others), one or more fixed-frequency oscillators (e.g., a reference or clock signal), a digital synthesizer, an information processor (e.g., a microprocessor), and/or other components.
• Thecontrol module206 may receive analog baseband frequency signals from thereceiver module216. The baseband frequency signals may be based on RF signals received from theRFID host102. The baseband frequency signals may include instructions to be executed by one or more processors included in thecontrol module206. For example, one or more processors included in thecontrol module206 may manipulate theswitching module208 to selectively control connections between the port202 and one or more of theantennas110. Thecontrol module206 may control and/or manipulate theswitching module208 using any type of communication interface. In some implementations, thecontrol module206 communicates with theswitching module208 through a one to four (1:4) control interface. For example, the 1:4 control interface may control a 1:4 switch included in theswitching module208. More generally, a 1:N control interface may be implemented to control a switch, such as a 1:N switch, included in theswitching module208.
• Thecontrol module206 may also send signals to thetag emulator module218. For example, thecontrol module206 may send a backscatter control signal to activate and/or deactivate a backscatter mode of the tag emulatemodule218. In some implementations, thecontrol module206 sends to the tag emulator module218 a response signal to include in a backscattered RF signal. For example, thetag emulator module218 may include the response signal in the backscattered RF signal by modulating the effective radio cross section of thetag emulator module218.
• Thecontrol module206 may receive power from one of or any combination of thecommunication module204, thepower tap module210, and/or theDC power module214. In some implementations, thepower tap module210 and/or theDC power module214 are not included in theRFID multiplexer108, and thecontrol module206 receives power only from thecommunication module204. In other implementations, the control module receives power from thecommunication module204 in addition to receiving power from at least one of thepower tap module210 or theDC power module214. In other implementations, thecontrol module206 only receives power from thepower tap module210 and/or theDC power module214. In some cases, the amount of power received from the communication module is less than a desired or required power, and thepower tap module210 and/or theDC power module214 are activated to provide supplemental power. In some cases, thepower tap module210 and/or theDC power module214 are present but inactive, providing no power to theRFID multiplexer108.
• Theswitching module208 selectively switchesantennas110 to the port202 and/or a different host coupling module. For example, theswitching module208 may include a one to four (1:4) switch that couples the port202 to one of fourantennas110. In other cases, the switching module may couple the port202 to more than oneantenna110, anotherRFID multiplexer108, and/or another device.
• Thepower tap module210 provides power to one or more components of theRFID multiplexer108 based on a DC signal component received through the host coupling module from theRFID host102. Thepower tap module210 may include capacitors, inductors, resistors, diodes, filters, amplifiers, and/or a variety of other electronic components. In some implementations, theRFID multiplexer108 receives from the RFID host102 a signal that includes an RF signal superposed on a DC signal. Thepower tap module210 may detect the DC signal component and provide power to the RF multiplexer based on the detected DC signal. For example, thepower tap module210 may separate the DC signal component out of the received signal and pass the DC signal component to thecontrol module206 through the illustrated Vcc connection. In some implementations, the DC power signal is passed to additional and/or different components. Thepower tap module210 may be implemented as a Bias-T DC power tap module, or any other suitable configuration.
• Thedirectional coupler212 provides signal direction-selective coupling between the host coupling module202, thecommunication module204, and theswitching module208. For example, signals sent from the port202 to theswitching module208 may also be received by thecommunication module204 through thedirectional coupler212, but signals sent from theswitching module208 to the port202 may bypass thecommunication module204. Similarly, signals sent from thecommunication module204 to the port202 may not be received by theswitching module208.
• TheDC power module214 provides power to one or more components of theRFID multiplexer108 from one or more external or internal sources. TheDC power module214 may be implemented as a battery, a wall plug, and/or any other power supply. In some cases, theDC power module214 may include an AC to DC converter for converting an AC signal (e.g. 60 Hz, 120 Hz, or others) to a DC power signal.
• Theantennas110 wirelessly receive and transmit RF signals between the tags104 and theRFID host102. For example, theantenna110 may transmit a query for information associated with the tag104, and theantenna110 may receive, in response to at least the inquiry, information including an identifier.
• In one aspect of operation, thecommunication module204 receives an RF signal from theRFID host102 through the port202. Thereceiver module216 detects the power of the received RF signal and communicates the measurement to thecontrol module206. Thecontrol module206 activates a backscatter mode, and thetag emulator module218 begins modulating impedance of the port202 to backscattered RF signals. Thetag emulator module218 may amplitude modulate and/or phase modulate the backscattered RF signals in order to modulate data to theRF host102. The response signal identifies the amount of received power. In some implementations, theDC power module214 can be activated to operate at least a portion of theRFID multiplexer108.
• In another aspect of operation, thecommunication module204 demodulates the received RF signals to baseband frequency signals and passes the baseband frequency signals to thecontrol module206. Thecontrol module206 converts the baseband frequency signals to digital signals, and based at least in part on the received signals, thecontrol module206 manipulates theswitching module208 to control coupling between the port202 and one ormore antennas110.
• In another aspect of operation, thepower tap module210 receives an RF signal from theRFID host102 through the port202. Thepower tap module210 detects a DC component of the received signal and provides power to thecontrol module206 based on the DC signal component. Thepower tap module210 passes the AC components of the received signal to one or more of theantennas110 for wireless transmission, for example, to tags104. If a response signal is received from a tag104, the response signal may be sent to theRFID host102 through the port202.
• FIG. 3 is a flow chart illustrating an example method300 for multiplexing RF signals. In general, the method300 may be used to operate an RF multiplexer based on power received from an RF host. In some implementations, the method300 can include the same, additional, fewer, and/or different steps.
• The method300 begins atstep302 where RF signals are received from an RFID host through a single wired connection. For example, theRFID multiplexer108 may receive RF signals from theRFID host102 through the wired connection114. If an antenna is identified based, at least in part, on the received RF signal atdecisional step304, then, atstep306, a plurality of antennas are selectively switched in accordance with the identified antenna. For example, themultiplexer108 may selectively switch theswitching module208 to connect the identified antenna to the pot202. Atstep308, at least a portion of the received RF signals is passed to the identified antenna and wirelessly transmitted, atstep310, to an RFID tag using the identified antenna. Returning todecisional step304, if the RF signal does not identify an antenna for transmission, then a request for information is identified atstep312. For example, themultiplexer108 may identify a request to identify transmitted power of the RF signal. Atstep314, a response is generated and transmitted, atstep316, by backscattering RF signals transmitted through the single wired connection. For example, themultiplexer108 may backscattered RF signals transmitted through the single wired connection114 to the RF host120.
• A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

Claims (16)

1-10. (canceled)

11. A radio frequency identification (RFID) multiplexer system, comprising:

a plurality of multiplexers connected in series including an initial multiplexer, the initial multiplexer comprising:

a port configured to receive RF signals from an RFID host; and

a communication module connected to the port and configured to demodulate the received RF signals to baseband frequency signals;

wherein at least one of the plurality of multiplexers is configured to selectively switch signals transmitted through an output port to subsequent multiplexers, the signals including RF signals and DC power.

12. The RFID multiplexer system ofclaim 11, wherein the communication module is configured to backscatter RF data via amplitude modulation or phase modulation.

13. The RFID multiplexer system ofclaim 12, wherein the backscattered RF data identifies information associated with one or more operating parameters of one of the plurality of RFID multiplexers.

14. The RFID multiplexer system of claim1, wherein the communication module further comprises a tag emulator module.

15. The RFID multiplexer system of claim1, further comprising a control module configured to selectively switch between a plurality of antennas based, at least in part, on received RF signals.

16. The RFID multiplexer system ofclaim 11, wherein the initial multiplexer is connected to a second RFID multiplexer through a second single wired connection such that DC and RF signals received from the RFID host can be passed to the second RFID multiplexer.

17. The RFID multiplexer system ofclaim 16, wherein the second single wired connection comprises a coaxial cable.

18. A method of controlling an RFID multiplexer, comprising:

receiving RF signals through a single wired connection to an RFID host, wherein the received RF signals include signals for wireless transmission and control signals for antenna switching;

transmitting to a plurality of multiplexers in series, Direct Current (DC) components combined with the received RF signals;

providing power for the multiplexer using the DC components;

transmitting to the plurality of multiplexers through the wired connection, the RF signals for wireless transmission and the control signals for antenna switching; and

backscattering at least a portion of the received RF signals in response to identifying requests for information, wherein the backscattered RF signals identify the detected components of the RF signals received from the RFID host.

19. The method ofclaim 18, further comprising:

demodulating at least a portion of the received RF signals to baseband frequency signals; and

selecting one antenna to wirelessly transmit at least a portion of the received RF signals based at least in part on the baseband frequency signals.

20. The method of claim10, wherein the baseband frequency signals are converted to digital signals.

21. A radio frequency identification (RFID) multiplexer comprising:

a port configured to perform at least one of the following operations: receive RF signals from an RFID host and provide RF signals and DC components to a second RFID multiplexer;

a receiver module configured to demodulate received RF signals into baseband frequency signals;

a module configured to backscatter a response to at least a portion of the received RF signals through the port;

a control module configured to perform at least one of the following operations:

receive baseband frequency signals, control a switching module, and backscatter control signals to the tag emulator module;

wherein the switching module is configured to selectively switch between antennas.

22. The RFID multiplexer ofclaim 21, wherein the control module further comprises at least one processor.

23. The RFID multiplexer ofclaim 22, wherein the baseband frequency signals include instructions to be executed by the at least one processor.

24. The RFID multiplexer ofclaim 21, wherein the baseband frequency signals are converted to digital baseband signals by the control module.

25. The RFID multiplexer ofclaim 21, further comprising a power tap module.

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