US20050083231A1 - Direct sampling gps receiver for anti-interference operations - Google Patents
Direct sampling gps receiver for anti-interference operations Download PDFInfo
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- US20050083231A1 US20050083231A1 US10/686,167 US68616703A US2005083231A1 US 20050083231 A1 US20050083231 A1 US 20050083231A1 US 68616703 A US68616703 A US 68616703A US 2005083231 A1 US2005083231 A1 US 2005083231A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/21—Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/21—Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
- G01S19/215—Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service issues related to spoofing
Definitions
- the present invention relates generally to global positioning system (GPS) receivers, and more particularly to a GPS receiver for anti-interference operations.
- GPS global positioning system
- GPS Global positioning systems, such as the US NAVSTAR GPS and Russian GLONASS, are known.
- the NAVSTAR GPS developed by the U.S. Department of Defense is a satellite-based radio navigation system that transmits information from which extremely accurate navigational calculations can be made in three-dimensional space anywhere on or near the Earth. Three-dimensional velocity can be determined with similar precision.
- GPS uses eighteen to twenty-four satellites that may be evenly dispersed in three inclined twelve-hour circular orbits chosen to ensure continuous twenty-four hour coverage worldwide.
- Each satellite uses extremely accurate cesium and rubidium vapor atomic clocks for generating a time base.
- Each satellite is provided with clock correction and orbit information by Earth-based monitoring stations.
- Each satellite transmits a pair of L-band signals.
- the pair of signals includes an L 1 signal at a frequency of 1575.42 MHz and an L 2 signal at a frequency of 1227.6 MHz.
- the L 1 and L 2 signals are biphase signals modulated by pseudo-random noise (PRN) codes and an information signal (i.e., navigation data) encoded at 50 Hz.
- PRN pseudo-random noise
- the PRN codes facilitate multiple access through the use of a different PRN code by each satellite.
- a receiver Upon detecting and synchronizing with a PRN code, a receiver decodes the PRN encoded signal to recover the navigation data, including ephemeris data.
- the ephemeris data is used in conjunction with a set of Keplerian equations to precisely determine the location of each satellite.
- the receiver measures a phase difference (i.e., time of arrival) of signals from at least four satellites. The time differences are then used to solve a matrix of four equations. The result is a precise determination of the location of the receiver in three-dimensional space.
- Velocity of the receiver may be determined by a precise measurement of the L 1 and L 2 frequencies. The measured frequencies are used to determine Doppler frequency shifts caused by differences in velocity. The measured differences are used to solve another set of equations to determine the velocity based upon the Doppler phase shift of the received signal.
- GPS For military applications, GPS allows self-guided weapons to find targets with heretofore unknown degrees of accuracy.
- GPS guidance systems use 10 watt signals from satellites in an eleven thousand nautical mile orbit. Consequently, such GPS systems are notoriously prone to interference, particularly man-made interference and RF jamming. Such compromises to GPS systems can adversely affect the navigation and precision of GPS-aided weapons.
- the susceptibility of GPS receivers to interference therefore necessitates an effective system for alleviating such problems.
- GPS anti-interference capability has been developed in the past, but has exhibited performance limitations. Such limitations have to do with classic receiver architectures involving RF mixers and synthesizers. Specifically, for example, such classic architectures are expensive and require precision components and tuning.
- a direct sampling global positioning system (GPS) receiver for anti-interference operations.
- the GPS receiver includes an input for receiving an analog interference signal at GPS frequencies.
- the GPS receiver includes an analog-to-digital converter (ADC), operatively coupled to the input, for converting the analog interference signal into a digital signal.
- the GPS receiver includes a processor for processing the digital signal to detect interference at the GPS frequencies and providing an output based thereon.
- ADC analog-to-digital converter
- a GPS anti-interference system for locating a source of the analog interference signal.
- the system includes an antenna array and a plurality of the above-mentioned GPS receivers.
- the inputs of the plurality of receivers are coupled to elements of the antenna array so as to receive the analog interference signal.
- Each of the plurality of receivers digitize the analog interference signal and a combined output of the plurality of receivers is indicative of the location of the source of the analog interference signal.
- a method for conducting direct sampling global positioning system (GPS) anti-interference operations includes the steps of receiving an analog interference signal at GPS frequencies; converting the analog interference signal into a digital signal; and processing the digital signal to detect interference at the GPS frequencies and providing an output based thereon.
- GPS global positioning system
- FIG. 1 is an environmental view of an operational environment including GPS guided weaponry and one or more GPS anti-interference systems in accordance with an embodiment of the invention
- FIG. 2 is a block diagram of an exemplary GPS anti-interference system in accordance with an exemplary embodiment of the present invention.
- FIG. 3 is a block diagram of an exemplary direct sampling GPS receiver for anti-interference operations in accordance with an exemplary embodiment of the present invention.
- FIG. 1 shown is a diagram depicting an operational environment including GPS guided weaponry and one or more GPS anti-interference systems in accordance with an embodiment of the invention.
- a missile 10 is guided to a target 12 using GPS signals from a satellite 14 .
- a small number of low cost jammers 16 may effectively defeat the system by introducing electromagnetic interference at the GPS frequencies (i.e., the carrier frequencies of the GPS signals, e.g., L 1 and L 2 ).
- the GPS link is lost is due to such interference, the missile 10 may drift considerably.
- the present invention addresses this problem by providing a low cost system for overcoming the effects of GPS interference. More particularly, the present invention relates to a low cost GPS receiver for detecting interference operations. Multiple GPS receivers may be part of one or more GPS anti-interference systems for detecting and locating jammers 16 .
- a GPS anti-interference system in accordance with the present invention may be located in an aircraft 20 .
- the system permits the aircraft 20 to detect and locate a jammer 16 .
- the aircraft 20 may then disable the jammer 16 by direct strike, providing location coordinates to another strike vehicle, etc.
- a ground based GPS anti-interference system in accordance with the invention may be utilized by ground personnel 22 , for example.
- the low cost GPS receivers allow ground personnel 22 to detect and locate a jammer 16 so that the jammer 16 may be disabled.
- a GPS anti-interference system in accordance with the invention may be utilized as part of a guidance system.
- a missile 24 may include low cost GPS receivers in accordance with the invention to detect, locate and lock onto a jammer 16 .
- FIG. 2 an exemplary configuration of a GPS anti-interference system 30 is shown in accordance with the present invention.
- the system 30 utilizes three GPS receivers 32 a , 32 b and 32 c , each of the type described below in relation to FIG. 3 .
- Each of the GPS receivers is designed to receive electromagnetic interference signals at the GPS frequencies.
- the system 30 is arranged in a conventional monopulse comparator configuration, for example, in which the outputs of the receivers 32 a , 32 b and 32 c are indicative of the location (azimuth and elevation) of the interference source (i.e., the jammer 16 ).
- FIG. 2 presents a diagrammatic representation of a monopulse comparator arithmetic network for providing sum, differential azimuth and differential elevation information by combining signals from four antenna ports designated A, B, C and D.
- the antenna ports are part of an antenna or antennas designed to receive electromagnetic interference signals at the GPS frequencies.
- the four ports may be regarded as associated with four beams each centered at the corner of a square centered about the antenna axis. Alternatively, the four antenna ports may be associated with separate antennas, for example.
- ports A and C are associated with beams in vertical alignment on one side of the square while ports C and D are associated with beams on the other side of the square in vertical alignment.
- the beams associated with ports A and B will then be in horizontal alignment separated from the beams associated with ports B and D in horizontal alignment by the antenna center axis.
- ports A and B are coupled by phase shifters 41 A and 41 B to hybrid junction 42 that provide their cumulative combination on branch 43 and their differential combination on branch 44 .
- ports C and D are coupled by phase shifters 41 C and 41 D to hybrid junction 45 which provides their cumulative combination on branch 46 and their differential combination on branch 47 .
- Lines 51 and 52 couple the signals from branches 44 and 47 , respectively, to hybrid junction 53 which provides their cumulative combination on branch 54 as the azimuth differential signal ⁇ H.
- the remaining branch 55 is terminated by impedance 56 .
- Lines 61 and 62 couple branches 43 and 46 to hybrid junction 63 which provides the cumulative combination of the signals on these branches on branch 64 as the sum signal ⁇ and their differential combination on branch 65 as the elevation differential signal ⁇ E.
- GPS receiver 32 a receives as its input the elevation differential signal ⁇ E.
- the GPS receivers 32 b and 32 c receive as inputs the sum signal ⁇ and azimuth differential signal ⁇ H, respectively.
- the inputs represent analog interference signals specifically at GPS frequencies.
- the precise azimuth and elevation of the source of the interference may be detected relative to the antenna(s), as is well known in the art.
- the present invention provides a means by which a source of interference signals at GPS frequencies may be detected and located.
- each of the receivers 32 a , 32 b and 32 c shown in FIG. 2 have the same configuration represented by the receiver 32 in FIG. 3 .
- the GPS receiver 32 is a direct sampling receiver.
- the analog interference signal at the GPS frequencies is sampled and digitized by an analog-to-digital converter without down-conversion to an intermediate or baseband signal.
- the GPS receiver 32 does not utilize the classic receiver architecture involving RF mixers and synthesizers. Consequently, the GPS receiver can be less expensive than such classic architecture and not require precision components and tuning.
- the GPS receiver 32 includes an input 70 for receiving the analog interference signal at GPS frequencies.
- the analog interference signal may be directly from an antenna or via a hybrid or the like (e.g., via line 54 , 64 or 65 of FIG. 2 ), for example.
- the input analog interference signal is input to a bandpass filter 72 included in the GPS receiver 32 .
- the bandpass filter 72 provides the filtered analog interference signal to an automatic gain control (AGC) limiter 74 also included in the GPS receiver 32 .
- AGC automatic gain control
- the AGC limiter 74 protects the internal circuitry of the GPS receiver 32 from being overdriven in the case of a high power interference signal (e.g., due to a high power jammer 16 , etc.). Using conventional techniques, the limiter 74 limits the maximum power level of the filtered analog interference signal.
- the analog interference signal is input from the limiter 74 to a radio frequency (RF) amplifier 76 included in the GPS receiver 32 .
- RF radio frequency
- the amplifier 74 amplifies the analog interference signal prior to it being input to an analog-to-digital converter (ADC) 78 also included in the GPS receiver 32 .
- ADC analog-to-digital converter
- the output of the amplifier 74 is fed back to the AGC limiter 74 via an AGC detector amplifier 80 so as to automatically control the gain.
- the limit of the AGC limiter 74 and the gains of the amplifiers 76 and 80 are selected so as to maximize use of the dynamic range of the ADC 78 .
- the ADC 78 directly samples the analog interference signal output from the amplifier 76 . There is no downconverting of the analog interference signal into an intermediate frequency or baseband signal frequency. Rather, the ADC 78 samples the analog interference signal without frequency conversion at a sample rate determined by a clock signal provided by a master reference unit (MRU) 82 . Such sampling rate may be on the order of about 2 Gigahertz (or 2 ⁇ 10 9 samples/second), or greater, for example.
- MRU master reference unit
- sampling frequency of 2 Ghz is less than twice the frequency of the GPS frequencies L 1 and L 2 , and thus does not satisfy the Nyquist criterion, sampling at such rate still is useful with regard to the invention. Specifically, detection of the energy at the GPS frequencies by the receivers 32 does not require the ability to detect any other frequencies that may be present in the analog interference signal. Of course, as ADCs having sample rates beyond 2 Ghz become more prevalent and economical, the entire frequency spectrum of the analog interference signal may be captured if desirable.
- the ADC 78 is a flash type (i.e., parallel bit) ADC.
- the GPS receiver 32 incorporating such an ADC can exhibit a minimum discernible signal (MDS) of ⁇ 60 dBm and a 1 dB input compression point (CP 1 ) of 0 dBm (with no AGC applied), without using the conventional superheterodyne approach.
- MDS minimum discernible signal
- CP 1 1 dB input compression point
- the dynamic range can be extended by using the AGC.
- Such a GPS receiver 32 allows for the detection of a 1 Kilowatt jammer 16 at up to about 20 kilometers (even without a low noise amplifier).
- the digitized interference signal is output from the ADC 78 into a digital signal processor (DSP) 84 that processes the signal in order to detect the presence of interference at the GPS frequencies.
- DSP digital signal processor
- the DSP 84 may employ a series of finite impulse response (FIR) filters designed to identify signals at the GPS frequencies within the digitized interference signal. Methods for designing and carrying out such FIR filters are well known, and therefore will not be described in detail for sake of brevity.
- FIR finite impulse response
- the output of the DSP 84 via output 86 indicates the magnitude of the RF energy detected by the GPS receiver 32 at the GPS frequencies. This information may then be combined with the output of the other GPS receivers 32 as shown in FIG. 2 , for example, to provide the exact location of the source of the GPS interference. Such location information may then be provided on a display 88 or the like, for example.
- the location information may be used by the pilot of an aircraft 20 ( FIG. 1 ) or ground personnel 22 to provide coordinates to eliminate the jammer 16 . Alternatively, the location information may be provided internally within a missile guidance system to direct the missile to strike the jammer 16 .
- the present invention provides a low cost system for overcoming the effects of GPS interference. More particularly, they will appreciate how the present invention relates to a low cost GPS receiver for detecting interference operations. Multiple GPS receivers may be part of one or more GPS anti-interference systems for detecting and locating the source of GPS interference.
Abstract
Description
- The present invention relates generally to global positioning system (GPS) receivers, and more particularly to a GPS receiver for anti-interference operations.
- Global positioning systems, such as the US NAVSTAR GPS and Russian GLONASS, are known. The NAVSTAR GPS developed by the U.S. Department of Defense is a satellite-based radio navigation system that transmits information from which extremely accurate navigational calculations can be made in three-dimensional space anywhere on or near the Earth. Three-dimensional velocity can be determined with similar precision. GPS uses eighteen to twenty-four satellites that may be evenly dispersed in three inclined twelve-hour circular orbits chosen to ensure continuous twenty-four hour coverage worldwide. Each satellite uses extremely accurate cesium and rubidium vapor atomic clocks for generating a time base. Each satellite is provided with clock correction and orbit information by Earth-based monitoring stations. Each satellite transmits a pair of L-band signals. The pair of signals includes an L1 signal at a frequency of 1575.42 MHz and an L2 signal at a frequency of 1227.6 MHz. The L1 and L2 signals are biphase signals modulated by pseudo-random noise (PRN) codes and an information signal (i.e., navigation data) encoded at 50 Hz. The PRN codes facilitate multiple access through the use of a different PRN code by each satellite.
- Upon detecting and synchronizing with a PRN code, a receiver decodes the PRN encoded signal to recover the navigation data, including ephemeris data. The ephemeris data is used in conjunction with a set of Keplerian equations to precisely determine the location of each satellite. The receiver measures a phase difference (i.e., time of arrival) of signals from at least four satellites. The time differences are then used to solve a matrix of four equations. The result is a precise determination of the location of the receiver in three-dimensional space. Velocity of the receiver may be determined by a precise measurement of the L1 and L2 frequencies. The measured frequencies are used to determine Doppler frequency shifts caused by differences in velocity. The measured differences are used to solve another set of equations to determine the velocity based upon the Doppler phase shift of the received signal.
- The utility of the GPS for guidance applications is well recognized. For military applications, GPS allows self-guided weapons to find targets with heretofore unknown degrees of accuracy. Unfortunately, GPS guidance systems use 10 watt signals from satellites in an eleven thousand nautical mile orbit. Consequently, such GPS systems are notoriously prone to interference, particularly man-made interference and RF jamming. Such compromises to GPS systems can adversely affect the navigation and precision of GPS-aided weapons. The susceptibility of GPS receivers to interference therefore necessitates an effective system for alleviating such problems.
- GPS anti-interference capability has been developed in the past, but has exhibited performance limitations. Such limitations have to do with classic receiver architectures involving RF mixers and synthesizers. Specifically, for example, such classic architectures are expensive and require precision components and tuning.
- Accordingly, there is a strong need in the art for a low cost system and method for overcoming the effects of interference in a GPS system.
- According to one aspect of the invention, a direct sampling global positioning system (GPS) receiver for anti-interference operations is provided. The GPS receiver includes an input for receiving an analog interference signal at GPS frequencies. In addition, the GPS receiver includes an analog-to-digital converter (ADC), operatively coupled to the input, for converting the analog interference signal into a digital signal. Moreover, the GPS receiver includes a processor for processing the digital signal to detect interference at the GPS frequencies and providing an output based thereon.
- In accordance with another aspect of the invention, a GPS anti-interference system is provided for locating a source of the analog interference signal. The system includes an antenna array and a plurality of the above-mentioned GPS receivers. The inputs of the plurality of receivers are coupled to elements of the antenna array so as to receive the analog interference signal. Each of the plurality of receivers digitize the analog interference signal and a combined output of the plurality of receivers is indicative of the location of the source of the analog interference signal.
- According to still another aspect of the invention, a method for conducting direct sampling global positioning system (GPS) anti-interference operations is provided. The method includes the steps of receiving an analog interference signal at GPS frequencies; converting the analog interference signal into a digital signal; and processing the digital signal to detect interference at the GPS frequencies and providing an output based thereon.
- To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
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FIG. 1 is an environmental view of an operational environment including GPS guided weaponry and one or more GPS anti-interference systems in accordance with an embodiment of the invention; -
FIG. 2 is a block diagram of an exemplary GPS anti-interference system in accordance with an exemplary embodiment of the present invention; and -
FIG. 3 is a block diagram of an exemplary direct sampling GPS receiver for anti-interference operations in accordance with an exemplary embodiment of the present invention. - The present invention will now be described with reference to the figures, wherein like reference numerals are used to refer to like elements throughout.
- Referring initially to
FIG. 1 , shown is a diagram depicting an operational environment including GPS guided weaponry and one or more GPS anti-interference systems in accordance with an embodiment of the invention. Conventionally, amissile 10 is guided to atarget 12 using GPS signals from asatellite 14. Unfortunately, as mentioned above, a small number oflow cost jammers 16 may effectively defeat the system by introducing electromagnetic interference at the GPS frequencies (i.e., the carrier frequencies of the GPS signals, e.g., L1 and L2). When the GPS link is lost is due to such interference, themissile 10 may drift considerably. - The present invention addresses this problem by providing a low cost system for overcoming the effects of GPS interference. More particularly, the present invention relates to a low cost GPS receiver for detecting interference operations. Multiple GPS receivers may be part of one or more GPS anti-interference systems for detecting and locating
jammers 16. - For example, a GPS anti-interference system in accordance with the present invention may be located in an
aircraft 20. Through the use of low cost GPS receivers as is explained in more detail below in relation toFIGS. 2 and 3 , the system permits theaircraft 20 to detect and locate a jammer 16. Theaircraft 20 may then disable the jammer 16 by direct strike, providing location coordinates to another strike vehicle, etc. - As another alternative, a ground based GPS anti-interference system in accordance with the invention may be utilized by
ground personnel 22, for example. Again, the low cost GPS receivers allowground personnel 22 to detect and locate a jammer 16 so that the jammer 16 may be disabled. - As yet another alternative, a GPS anti-interference system in accordance with the invention may be utilized as part of a guidance system. For example, a
missile 24 may include low cost GPS receivers in accordance with the invention to detect, locate and lock onto ajammer 16. - Turning now to
FIG. 2 , an exemplary configuration of aGPS anti-interference system 30 is shown in accordance with the present invention. Thesystem 30 utilizes threeGPS receivers FIG. 3 . Each of the GPS receivers is designed to receive electromagnetic interference signals at the GPS frequencies. Thesystem 30 is arranged in a conventional monopulse comparator configuration, for example, in which the outputs of thereceivers -
FIG. 2 presents a diagrammatic representation of a monopulse comparator arithmetic network for providing sum, differential azimuth and differential elevation information by combining signals from four antenna ports designated A, B, C and D. The antenna ports are part of an antenna or antennas designed to receive electromagnetic interference signals at the GPS frequencies. The four ports may be regarded as associated with four beams each centered at the corner of a square centered about the antenna axis. Alternatively, the four antenna ports may be associated with separate antennas, for example. - In the exemplary embodiment, ports A and C are associated with beams in vertical alignment on one side of the square while ports C and D are associated with beams on the other side of the square in vertical alignment. The beams associated with ports A and B will then be in horizontal alignment separated from the beams associated with ports B and D in horizontal alignment by the antenna center axis.
- The signals from ports A and B are coupled by
phase shifters hybrid junction 42 that provide their cumulative combination onbranch 43 and their differential combination onbranch 44. Similarly ports C and D are coupled byphase shifters hybrid junction 45 which provides their cumulative combination onbranch 46 and their differential combination onbranch 47. -
Lines branches hybrid junction 53 which provides their cumulative combination onbranch 54 as the azimuth differential signal ΔH. The remainingbranch 55 is terminated byimpedance 56.Lines couple branches hybrid junction 63 which provides the cumulative combination of the signals on these branches onbranch 64 as the sum signal Σ and their differential combination onbranch 65 as the elevation differential signal ΔE. - As is shown in
FIG. 2 ,GPS receiver 32 a receives as its input the elevation differential signal ΔE. Similarly, theGPS receivers GPS receivers - Referring now to
FIG. 3 , a configuration of a lowcost GPS receiver 32 for anti-interference operations is shown in accordance with the exemplary embodiment of the present invention. As will be appreciated, each of thereceivers FIG. 2 have the same configuration represented by thereceiver 32 inFIG. 3 . - The
GPS receiver 32 is a direct sampling receiver. The analog interference signal at the GPS frequencies is sampled and digitized by an analog-to-digital converter without down-conversion to an intermediate or baseband signal. TheGPS receiver 32 does not utilize the classic receiver architecture involving RF mixers and synthesizers. Consequently, the GPS receiver can be less expensive than such classic architecture and not require precision components and tuning. - As shown in
FIG. 3 , theGPS receiver 32 includes aninput 70 for receiving the analog interference signal at GPS frequencies. The analog interference signal may be directly from an antenna or via a hybrid or the like (e.g., vialine FIG. 2 ), for example. The input analog interference signal is input to abandpass filter 72 included in theGPS receiver 32. Thebandpass filter 72 has a passband that includes the GPS frequencies (e.g., L1=1575.42 MHz and L2=1227.6 MHz), and that filters out frequencies above and below the GPS frequencies. - The
bandpass filter 72 provides the filtered analog interference signal to an automatic gain control (AGC) limiter 74 also included in theGPS receiver 32. TheAGC limiter 74 protects the internal circuitry of theGPS receiver 32 from being overdriven in the case of a high power interference signal (e.g., due to ahigh power jammer 16, etc.). Using conventional techniques, thelimiter 74 limits the maximum power level of the filtered analog interference signal. The analog interference signal is input from thelimiter 74 to a radio frequency (RF)amplifier 76 included in theGPS receiver 32. Theamplifier 74 amplifies the analog interference signal prior to it being input to an analog-to-digital converter (ADC) 78 also included in theGPS receiver 32. In addition, the output of theamplifier 74 is fed back to theAGC limiter 74 via anAGC detector amplifier 80 so as to automatically control the gain. - The limit of the
AGC limiter 74 and the gains of theamplifiers ADC 78. In accordance with the present invention, theADC 78 directly samples the analog interference signal output from theamplifier 76. There is no downconverting of the analog interference signal into an intermediate frequency or baseband signal frequency. Rather, theADC 78 samples the analog interference signal without frequency conversion at a sample rate determined by a clock signal provided by a master reference unit (MRU) 82. Such sampling rate may be on the order of about 2 Gigahertz (or 2×109 samples/second), or greater, for example. - It is noted that although a sampling frequency of 2 Ghz is less than twice the frequency of the GPS frequencies L1 and L2, and thus does not satisfy the Nyquist criterion, sampling at such rate still is useful with regard to the invention. Specifically, detection of the energy at the GPS frequencies by the
receivers 32 does not require the ability to detect any other frequencies that may be present in the analog interference signal. Of course, as ADCs having sample rates beyond 2 Ghz become more prevalent and economical, the entire frequency spectrum of the analog interference signal may be captured if desirable. - In the exemplary embodiment, the
ADC 78 is a flash type (i.e., parallel bit) ADC. For example, there are now commercially available 10-bit, 2×109 samples/second ADCs suitable for use in accordance with the invention. TheGPS receiver 32 incorporating such an ADC can exhibit a minimum discernible signal (MDS) of −60 dBm and a 1 dB input compression point (CP1) of 0 dBm (with no AGC applied), without using the conventional superheterodyne approach. The dynamic range can be extended by using the AGC. Such aGPS receiver 32 allows for the detection of a 1Kilowatt jammer 16 at up to about 20 kilometers (even without a low noise amplifier). - The digitized interference signal is output from the
ADC 78 into a digital signal processor (DSP) 84 that processes the signal in order to detect the presence of interference at the GPS frequencies. For example, theDSP 84 may employ a series of finite impulse response (FIR) filters designed to identify signals at the GPS frequencies within the digitized interference signal. Methods for designing and carrying out such FIR filters are well known, and therefore will not be described in detail for sake of brevity. - The output of the
DSP 84 viaoutput 86 indicates the magnitude of the RF energy detected by theGPS receiver 32 at the GPS frequencies. This information may then be combined with the output of theother GPS receivers 32 as shown inFIG. 2 , for example, to provide the exact location of the source of the GPS interference. Such location information may then be provided on adisplay 88 or the like, for example. The location information may be used by the pilot of an aircraft 20 (FIG. 1 ) orground personnel 22 to provide coordinates to eliminate thejammer 16. Alternatively, the location information may be provided internally within a missile guidance system to direct the missile to strike thejammer 16. - Those having ordinary skill in the art will therefore appreciate the manner in which the present invention provides a low cost system for overcoming the effects of GPS interference. More particularly, they will appreciate how the present invention relates to a low cost GPS receiver for detecting interference operations. Multiple GPS receivers may be part of one or more GPS anti-interference systems for detecting and locating the source of GPS interference.
- While the present invention is described herein with reference to illustrative embodiments for particular applications (e.g., weapons guidance), it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
- Although the invention has been shown and described with respect to certain preferred embodiments, it is obvious that equivalents and modifications will occur to others skilled in the art upon the reading and understanding of the specification. For example, while the invention has been described primarily in the context of detecting man-made intentional interference (e.g., jammers 16), it will be appreciated that the present invention is equally applicable to detecting other types of interference. The present invention includes all such equivalents and modifications, and is limited only by the scope of the following claims.
Claims (19)
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US20090170466A1 (en) * | 2007-12-31 | 2009-07-02 | Industrial Technology Research Institute | Circuit with programmable signal bandwidth and method thereof |
US20100045506A1 (en) * | 2008-08-22 | 2010-02-25 | Raytheon Company | Method And System For Locating Signal Jammers |
US20100120386A1 (en) * | 2008-11-12 | 2010-05-13 | Doris Konstantinos | Multi-Channel Receiver Architecture and Reception Method |
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