US20060055594A1 - Method and apparatus for reducing GPS receiver jamming during transmission in a wireless receiver - Google Patents

Abstract

A method and apparatus for minimizing the interference between wireless transmissions and a proximately located or co-located GPS receiver is disclosed. By feedforward of a phase and amplitude adjusted version of the transmitted signal and combining said signal with the composite signal at the input of the GPS receiver, the GPS receiver sensitivity degradation is reduced or eliminated in the case of perfect cancellation, and the GPS receiver is not jammed by the wireless transmissions. The invention allows a single antenna to be implemented for GPS reception and wireless transmission and reception without unduly complicating the diplexing/filtering network required to separate the multiple signals being transmitted and/or received by the single antenna.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims priority under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/224,741, filed Aug. 10, 2000, entitled “METHOD AND APPARATUS FOR REDUCING GPS RECEIVER JAMMING DURING TRANSMISSION IN A WIRELESS TRANSCEIVER,” by Richard J. McConnell, et al., which application is incorporated by reference herein.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates in general to wireless transceivers integrated with a Global Positioning System (GPS) receiver, and in particular to a method and apparatus for reducing GPS receiver jamming during transmission by the wireless transceiver.
• 2. Description of the Related Art
• Wireless communications systems, including cellular telephony, Personal Communication System (PCS) devices, Personal Data Assistants (PDAs), and other wireless handsets and devices, has become commonplace. The use of such devices to provide voice, data, and other services, such as internet access, has provided many conveniences to wireless system users.
• Currently, designers are integrating Global Positioning System (GPS) technology into wireless devices and other wireless transceivers. The GPS system transmits at 1.575 GHz, and the cellular and PCS systems transmit at 900 MHz and 1.9 GHz, respectively. Inherent in a device that combines GPS reception and wireless transmission circuitry, which circuitry includes an antenna, undesired electromagnetic coupling between the transmitter of the wireless transceiver and the GPS receiver will occur. Since cellular devices (handsets) are typically small in size, it is desirable to have a device that can share an antenna for use by both the GPS receiver and the wireless transceiver, if this is possible without deleterious performance effects on either system.
• Since the cellular and PCS transmitted signals are extremely strong signals relative to the GPS received signals, and these strong signals or their harmonics can degrade the sensitivity of the GPS receiver during wireless transceiver transmission, unless filtering or other methods are employed to reject the interfering or jamming signal. As such, the reliability and operation of GPS receivers that are used in conjunction with cellular handsets is degraded.
• It can be seen, then, that there is a need in the art for a method of reducing the effects of wireless transmissions on proximate GPS receivers. It can also be seen that there is a need in the art for an apparatus that can reduce the effects of wireless transmissions on GPS receivers. It can also be seen that there is a need in the art for a method and apparatus that can allow GPS receivers and wireless transmitters to share a common antenna.
SUMMARY OF THE INVENTION
• To minimize the limitations in the prior art, and to minimize other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for minimizing the interference between wireless transmissions and the proximate or co-located GPS receiver. By feedforward of a phase and amplitude adjusted version of the transmitted signal and combining said signal with the composite signal at the input of the GPS receiver, the GPS receiver sensitivity degradation is reduced or eliminated in the case of perfect cancellation, and the GPS receiver is not jammed by the wireless transmissions. Further, a single antenna can be used for GPS reception and wireless transmission and reception without unduly complicating the diplexing/filtering network required to separate the multiple signals being transmitted and/or received by the single antenna.
• An apparatus in accordance with the present invention comprises a GPS receiver, an antenna, coupled to the GPS receiver, a transceiver, a second antenna, coupled to the transceiver, coupling means, and a phase and gain adjusting means. The coupling means obtains a replica signal from the transceiver, which is selectively phase and gain adjusted and then is provided to the GPS receiver. The selectively phase and gain adjusted replica signal reduces interference between a transmitted signal from the transceiver and a signal received by the GPS receiver.
• It is an object of the present invention to provide a method of reducing the effects of wireless transmissions on proximate GPS receivers. It is another object of the present invention to provide an apparatus that can reduce the effects of wireless transmissions on GPS receivers. It is a further object of the present invention to provide a method and apparatus that allows GPS receivers and wireless transceivers to share a common antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
• Referring now to the drawings in which like reference numbers represent corresponding parts throughout:
• FIG. 1 illustrates the electromagnetic interference between the wireless and the GPS systems;
• FIG. 2 illustrates a system in accordance with the present invention; and
• FIG. 3 is a flowchart illustrating the steps used to practice the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
• In the following description of the preferred embodiment, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration a specific embodiment in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.
• Overview
• It is a known problem that strong signals that fall within or near the GPS RF band will desensitize GPS receiver performance. Since cellular/PCS transmissions can introduce spurrious signals, or overdrive the GPS receiver, solving and/or minimizing the effects of such signals is of special interest for wireless handsets which contain a GPS receiver that must operate during a wireless transmission. Typically in such handsets, the wireless antenna and the GPS antenna are in close proximity or, preferably for low cost, are the same antenna, and the coupling of transmitted power is significant and likely to degrade GPS performance. The present invention describes a method of avoiding or greatly reducing the degree of GPS desensitization that occurs.
• Although described herein with respect to cellular/PCS interference with GPS receivers, the interference phenomenon is present for any signals that are of a frequency near or within the GPS receiver band, as well as signals that have harmonics that fall near or within the GPS receiver band, or any signals that degrade the GPS receiver. The present invention is not limited to cellular and/or PCS applications, but can be used to reduce or eliminate the degradation of GPS receiver sensitivity in other wireless transceiver and GPS receiver applications and/or environments.
• System Overview
• The present invention provides a system solution that uses additional circuitry between the wireless transceiver and GPS receiver, and within the GPS RF front end circuits. A correction “replica” signal is obtained from the power-amplifier section of the wireless transceiver. The replica signal is then provided to the GPS receiver as an interference cancellation signal. The combined wireless transceiver and GPS receiver contains circuitry that allows digitally controlled adjustment of the amplitude and phase of the replica signal, such that when added with the composite signal received by the GPS front end, the net power of undesired wireless signal in said GPS circuit is minimized or nulled.
• The GPS front end circuitry includes a detector which provides the system a relative indication of the power level of the received wireless signal. This signal is digitized and the information is provided to a digital controller, which is typically integrated with the baseband processor. Effectively the system implements a cancellation feedback algorithm, and the immunity of the GPS receiver is achieved independent of the physical design of the handset, allowing great flexibility for the handset designer in selecting the degree of co-location of the GPS and wireless antennas, including the highly desirable case of using a single multi-band antenna. Furthermore, the method requires very little duty factor usage of the receiver's processor or controller. Further, the present invention is useful in handsets of different manufacturers, since the feedback technique of the present invention is useful regardless of handset design.
• Block Diagrams
• FIG. 1 illustrates the electromagnetic interference between the cellular and the GPS systems.System100 comprises awireless transceiver antenna102, which is coupled to aduplexer104. Duplexer104 allows theantenna102 to be used alternatively or simultaneously by a transmitter amplifier (power amplifier (PA))106 and a receiver amplifier (Low Noise Amplifier (LNA))108. LNA108 is coupled to abandpass filter110, which is coupled to afrequency converter112.PA106 is also coupled to abandpass filter114, which is coupled to thefrequency converter112.Frequency converter112 is coupled to the IF, frequency synthesis and wireless baseband processor andcontroller116.
• System100 also comprises aGPS antenna118, which may be the same antenna asantenna102, but, for ease of illustration of the problem to be solved by the present invention, is shown as aseparate antenna118.Antenna118 is coupled to a pre-select Radio Freqency (RF)filter120, which is coupled to anamplifier122. The output ofamplifier122 is coupled to anotherbandpass filter124, which is then input tofrequency converter126. The output offrequency converter126 is delivered to a GPS processor andcontroller128.GPS receiver136 comprisesantenna118,filter120,amplifier122,filter124,frequency converter126, andcontroller128.
• Whenantenna102 is transmittingsignal130, aninterference signal132 occurs whenantenna102 is transmitting wireless system voice data and/or digital or analog data. Since theinterference signal132 so strong and real filters have limited stop band capability, theGPS receiver136 is desensitized by such a signal either by intermodulation mixing effects which occur withinamplifier122, or by GPS in band interference contained insignal130.
• FIG. 2 illustrates a system in accordance with the present invention.System200 is similar tosystem100, but uses feedback to assistsystem200 in canceling theinterference signal132 onGPS receiver136.
• Coupler202 couples a replica version of the transmitted signal output ofPA106, and delivers the replica signal toblocks204 and206.Blocks204 and206 can control the phase and amplitude of the replica signal, and blocks204 and206 generate resultingsignal208.Coupler210 thencouples resulting signal208 into theGPS amplifier122 input.
• The phase and amplitude of resultingsignal208 is adjusted bycontroller128, which can alter the phase and amplitude ofsignal208 viacontrol signal paths212 and214 respectively. To determine how to controlblocks204 and206 usingcontroller128, Receive Signal Strength Indicator (RSSI)216 is coupled to the incoming received signal after theGPS amplifier122, and the output ofRSSI216 is fed intocontroller128. Theoutput signal218 ofRSSI216 is monitored bycontroller128. The phase and amplitude ofsignal208 are iteratively adjusted according to a minimization search routine, which can be programmed by software in the controller. By properly adjusting the phase and amplitude ofsignal208 viacontroller128 and blocks204 and206, the effects of interferingsignal132 can be reduced or eliminated.
• In most designs, theinterference signal132 will be fixed in phase and amplitude once the wireless device is designed, and the only effects that blocks204 and206 will be required to adaptively cancel are long-term drift effects generated insystem200, or changes of thesignal132 due to external environment changes which affect the coupling betweenantenna102 and118. As such, the added overhead burden of the invention uponcontroller128 will cause insignificant power increase after initial setting of the phase and amplitude adjusters withinblocks204 and206. Further, the feedback loop described in the present invention can be used with any handset design, because the feedback loop can control wide variations of the phase and amplitude of interferingsignal132.
• Ifantennas102 and118 are a single antenna,filter120 now filters out most of the transmit signal from transmitamplifier108, but cannot do so perfectly, since real filters have non-infinite out-of-band rejection, and therefore some of the transmit signal will be received at theGPS receiver136. The present invention allows the performance requirements offilter120 to be relaxed, since the feedback loop created byblocks204 and206 allows those portions of the transmitted signal that do pass throughfilter120 to be canceled out bysignal208. Further, the feedback loop can be closed using feedback directly from theGPS receiver136 instead of through theRSSI216 if desired. If desired, thebaseband controller116 and theGPS controller128 can be combined into asingle controller220.
• Process Chart
• FIG. 3 is a flowchart illustrating the steps used to practice the present invention.
• Block300 illustrates replicating a transmission of the transceiver.
• Block302 illustrates coupling the replicated transmission into a front end of the GPS receiver.
• Block304 illustrates at least partially canceling the transmission using the replicated transmission.
• Conclusion
• This concludes the description of the preferred embodiment of the invention. The following paragraphs describe some alternative methods of accomplishing the same objects. The present invention, although described with respect to GPS systems, can be utilized with any Satellite Positioning System (SATPS) without departing from the scope of the present invention. Further, although described with respect to a specific transceiver system, such as the cellular telephone system, other wireless or wire-based systems, such as Personal Data Assistants, mobile computers, Personal Communications Systems, wireless Local Area Networks (LANs), wireless LANs that are compatible with the “Bluetooth” standards, or other wireless or wire-based systems, can be used in place of or in conjunction with the cellular system herein described without departing from the scope of the present invention. Further, the present invention is useful with transmitters as well as transceivers without departing from the scope of the present invention.
• In summary, the present invention discloses a method and apparatus for reducing GPS receiver jamming during transmission in a wireless transceiver. An apparatus in accordance with the present invention comprises a GPS receiver, an antenna, coupled to the GPS receiver, a transceiver, a second antenna, coupled to the transceiver, coupling means, and a phase and gain adjusting means. The coupling means obtains a replica signal from the transceiver, which is selectively phase and gain adjusted and then is provided to the the GPS receiver. The selectively phase and gain adjusted replica signal reduces interference between a transmitted signal from the transceiver and a signal received by the GPS receiver.
• The foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. It is intended that the scope of the invention not be limited by this detailed description, but by the claims appended hereto.

Claims (17)

1. A wireless mobile terminal system comprising:

a GPS receiver;

an antenna, coupled to the GPS receiver, for allowing the GPS receiver to receive GPS signals transmitted from at least one GPS satellite;

a wireless transceiver;

a second antenna, coupled to the transceiver, for allowing the transceiver to transmit signals and further for allowing the transceiver to receive signals;

a first coupling means, coupled to the transceiver, for obtaining a replica signal from the transceiver, the replica signal being a replica of a signal being transmitted by the transceiver;

a phase and gain adjusting means, with an input coupled to the first coupling means, for accepting and selectively conditioning the replica signal; and

a second coupling means, coupled to the output of the phase and gain adjusting means, for providing the selectively phase and gain adjusted replica signal to the GPS receiver, wherein the selectively phase and gain adjusted replica signal reduces interference between a transmitted signal from the transceiver and a signal received by the GPS receiver.

2. The GPS receiver system ofclaim 1, wherein the antenna and the second antenna are a single antenna.

3. The GPS receiver system ofclaim 2, wherein the phase and gain adjusting means uses a feedback loop to reduce the interference between the transmitted signal from the transceiver and the signal received by the GPS receiver.

4. The GPS receiver system ofclaim 3, wherein the replica of the transmitted signal is used to cancel interference between the transmitted signal and the signal received by the GPS receiver.

5. The GPS receiver system ofclaim 4, wherein the replica of the transmitted signal is adjusted in phase.

6. The GPS receiver system ofclaim 5, wherein the replica of the transmitted signal is shifted in amplitude.

7. The GPS receiver system ofclaim 6, wherein the phase shift of the transmitted signal and the amplitude shift of the transmitted signal are controlled by a received signal strength indicator.

8. The GPS receiver system ofclaim 7, wherein the combining circuit further comprises an adaptive circuit.

9. The GPS receiver system ofclaim 8, wherein the adaptive circuit minimizes long-term drift effects.

10. A method for reducing interference in a Global Positioning System (GPS) receiver that shares an antenna with a transceiver, comprising the steps of:

replicating a first transmission of the transceiver, wherein the first transmission of the transceiver emanates from an antenna receiving GPS signals;

coupling the replicated transmission into a front end of the GPS receiver; and

at least partially canceling the first transmission using the replicated transmission.

11. The method ofclaim 10, wherin the partial cancellation is performed using a feedback loop.

12. The method ofclaim 11, wherein the feedback loop uses a replica of the transmitted signal.

13. The method ofclaim 12, further comprising phase shifting the replicated signal.

14. The method ofclaim 13, further comprising amplitude shifting the replicated signal.

15. The method ofclaim 14, further comprising controlling the phase shifting of the replicated signal and the amplitude shifting of the replicated signal by using a received signal strength indicator.

16. The method ofclaim 15, further comprising minimizing long-term drift effects.

17. The method ofclaim 16, wherein the minimizing of long-term drift effects is performed by an adaptive circuit.

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