MITIGATING INTERFERENCE IN A SIGNAL

• US 20090141775A1
• Filed: 02/23/2006
• Published: 06/04/2009
• Est. Priority Date: 02/25/2005
• Status: Active Grant

• Current Assignee: Data Fusion Corp.
• Original Assignee: Data Fusion Corp.
• Inventors: Kadlec, Steven Alan, Reynolds, Lewis, Krumvieda, Robert Kent, Kober, Wolfgang
• Granted Patent: US 7,626,542 B2
• Time in Patent Office: Days
• US Class Current: 375/148
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal

Abstract

A method and receiver are disclosed for mitigating or substantially canceling signal interference between signals detected at the receiver. Once a presumed interfering signal(s) is acquired, parameters are determined that allow the interferer(s) to be modeled. The phase invariance of the process eliminates the need to acquire the interferer'"'"'s phase. An orthogonal projection (for projecting onto a detection subspace which is orthogonal to a subspace spanned by the interferer(s)) is applied to the composite of all signals (y) for thereby projecting y onto the detection subspace. The interference subspace is non-orthogonal to a representation of desired (but interfered) signal of the composite signals. With the receiver properly equipped to perform this projection operation, interfering signals, multipath, multipath-like, and structured jamming signals can be effectively diminished.

Claims

1. A signal processing method, comprising:

(a) an antenna receiving a composite signal (y), wherein y includes, from each of a plurality of signaling sources, at least one corresponding wireless signal comprising information;

(b) obtaining, for each selected wireless signal in the composite signal, signal modeling data;

(c) based on the signal modeling data for each selected wireless signal, determining a respective model, each respective model containing both in phase and quadrature components of the corresponding selected wireless signal;

(d) performing a projection of a representation of y onto a detection subspace to remove all of at least one interfering wireless signal (s₀) from at least one known interfering signaling source, the detection subspace being orthogonal to a complex interference subspace spanning a representation of the at least one interfering signal s₀ of the corresponding wireless signals, wherein said interference subspace is determined using said respective signal modeling data for the at least one interfering signal s₀, wherein said detection subspace is non-orthogonal and non-equivalent to a signal-of-interest subspace spanning a representation of another signal (h_O) of said corresponding wireless signals, and wherein step (d) is performed without estimating a phase of one or more of the at least one interfering wireless signal s₀;

(e) using a result from said step of performing for acquiring said another corresponding signal h_O; and

(f) after acquiring the signal h_O, determining the information from the signal h_O.

2. The method of claim 1, wherein the composite signal is sampled to provide both the in phase and quadrature components of the composite signal and wherein the interference subspace does not include a representation of the signal h_O.

3. The method of claim 1, wherein the signal modeling data of each selected wireless signal comprises estimates of time offset, a Doppler data, and a signal frequency and not of phase, wherein the representation of the signal h_O is characterized by a respective signal model and wherein the model represents the in phase and quadrature components of the signal h_O.

4. The method of claim 3, wherein the respective model for each of the selected wireless signals, including signal h_o, comprises both a real component and a complex component and excludes a phase estimate.

5. The method of claim 3, wherein the respective modeling data for the at least one interfering signal s₀ does not include the phase of the at least one interfering signal s₀ and wherein the respective modeling data is dependent upon one or more of (a) a coarse acquisition code and a carrier frequency and (b) a coarse acquisition code, a precise positioning code, and a carrier frequency.

6. The method of claim 1, wherein the respective signal modeling data comprises estimates of a pseudo-random number, code offset data, and Doppler data and excludes a phase estimate, wherein the information in the selected wireless signals is navigation data, wherein said navigation data comprises one or more of a telemetry word, hand-over word, clock correction, SV health/accuracy, ephemeris parameter, almanac data, and ionospheric model data, and further comprising:

determining navigation information using the navigation data from a plurality of said selected wireless signals including the signal h_O, and wherein the navigation information comprises data identifying one or more of;

a position, a velocity, and time for the antenna.

7. The method of claim 1, wherein step (d) is performed without input from a Phase Locked Loop (PLL) and further comprising:

identifying, for each of the selected wireless signals, a corresponding set of interfering signals, wherein a first wireless signal has a first set of interfering signals, wherein a second wireless signal has a second set of interfering signals, wherein the memberships of the first and second sets are different, wherein the first and second sets are created after each of the selected wireless signals has been acquired and tracked, wherein the acquiring and tracking comprises obtaining, as at least part of the corresponding signal modeling data, two or more of a pseudo-random number, code offset data, Doppler data, code offset rate, and Doppler rate, and wherein the identification of a signal as an interfering signal is based on threshold criteria that includes at least one of;

(a) a predetermined number of the strongest of said corresponding signals, (b) a predetermined decibel increase above a predetermined value, (c) a signal-to-noise ratio, (d) a signal-to-carrier ratio, (e) a carrier-to-noise ratio, (f) a relative amplitude, and (g) a weighted sum of two or more of (a) through (f).

8. The method of claim 1, further including a step of constructing a reference signal from the signal modeling data for s_O, the reference signal being used to determine said complex interference subspace, wherein the reference signal for s_O has the following representation:

s_o=sI₀+i*sQ₀

wherein the reference signal for s₀ is composed of a real component sI₀, which is a column vector containing the in-phase component, and a complex component i*sQ₀, where i=sqrt(−

1) and sQ₀, which is a column vector containing the quadrature component.

9. The method of claim 1, wherein each of the signal models is complex and wherein the selected wireless signals have unequal powers and wherein the obtaining step comprises the substeps:

(b1) tracking and acquiring the wireless signal h₀ having a first power; and

(b2) identifying each of the plurality of wireless signals having a power greater than the first magnitude as an interferer and those having a power less than the first magnitude as a noninterferer;

wherein in the performing step (d) the at least one interfering signal (s₀) comprises only the signals identified as interferers

10. The method of claim 1, wherein the selected wireless signals have unequal powers and wherein the obtaining step comprises:

(b1) tracking and acquiring at least some of the plurality of selected wireless signals;

(b2) grouping the tracked and acquired selected wireless signals based on the relative powers of the signals; and

(b3) for each ungrouped selected wireless signal, performing step (d), wherein the at least one interfering signal (s₀) comprises the grouped selected wireless signals;

wherein step (e) is performed for each ungrouped selected wireless signal

11. The method of claim 1, wherein each of the respective models is complex, wherein the complex interference subspace in step (d) is multiplied by a complex conjugate, and wherein the projection of a representation of y onto the detection subspace is performed using at least one adjoint operator.

12. A computer readable medium comprising processor executable instructions to perform the steps of claim 1.

13. A logic circuit operable to perform the steps of claim 1.

26. The method of claim 3, wherein the respective model for each of the selected wireless signals, including signal h_o, comprises both a real component and a complex component and excludes a phase estimate.

28. The signal processing method of claim 1, wherein step (d) removes substantially all interfering wireless signals from known interfering signaling sources from the composite signal y to permit acquisition of signal h_O.

14. A signal processing system, comprising:

(a) an antenna operable to receive a composite signal (y), the composite signal y including, from each of a plurality of signaling sources, at least one corresponding wireless signal comprising signaling information;

(b) a matched subspace detector operable to;

(i) obtain, for each selected wireless signal in the composite signal, respective signal modeling data indicative of the corresponding wireless signal,

(ii) based on the signal modeling data for each selected wireless signal, determining a respective model, each respective model containing both in phase and quadrature components of the corresponding selected wireless signal and excludes a phase estimate; and

(iii) project a representation of y onto a detection subspace to remove all of at least one interfering wireless signal (s₀) from at least one known interfering signaling source, the detection subspace being orthogonal to an interference subspace spanning a representation of the at least one interfering signal s₀ of the corresponding wireless signals, wherein said interference subspace is determined using said respective signal modeling data for the at least one interfering signal s₀ and wherein said detection subspace is non-orthogonal and non-equivalent to a signal-of-interest subspace spanning a representation of another signal (h_O) of said corresponding wireless signals; and

(c) a processing channel operable, based on a result of the projection, to acquire said another corresponding signal h_O and, after acquiring the signal h_O, determine the information from the signal h_O.

15. The system of claim 14, wherein the interference subspace is complex and further comprising:

(d) a pre-amplifier operable to amplify the power of the received composite signal;

(e) a down converter operable to down convert, using signal mixing frequencies, and provide down converted in phase and quadrature components of the composite signal y;

(f) an oscillator operable to provide the signal mixing frequencies to the down converter;

(g) an analog-to-digital converter operable to convert the down-converted in phase and quadrature from analog to digital format; and

(h) a data store operable to store the signal modeling data for each of the tracked and acquired plurality of wireless signals.

16. The system of claim 14, wherein the composite signal is sampled to provide both the down-converted in phase and quadrature components of the composite signal, wherein operation (iii) is performed without estimating a phase of one or more of the selected wireless signals, and wherein the interference subspace does not include a representation of the signal h_O.

17. The system of claim 14, wherein the interference subspace is complex, wherein the representation of the signal h_O is characterized by a respective signal model, and wherein the model represents the in phase and quadrature components of the signal h o.

18. The system of claim 17, wherein the model for each of the corresponding wireless signals, including signal ho, comprises both a real component and a complex component.

19. The system of claim 17, wherein the modeling data for at least one interfering signal s0 does not include the phase of the modeled signal and wherein the modeling data is dependent upon one or more of (a) a coarse acquisition code and a carrier frequency and (b) a coarse acquisition code, a precise positioning code, and a carrier frequency.

20. The system of claim 14, wherein the respective signal modeling data comprises a pseudo-random number, code offset data, and Doppler data, wherein the information in the wireless signals is navigation data, wherein said navigation data comprises one or more of a telemetry word, hand-over word, clock correction, SV health/accuracy, ephemeris parameter, almanac data, and ionospheric model data, and further comprising:

determining navigation information using the navigation data from a plurality of said wireless signals including the signal h_O, and wherein the navigation information comprises data identifying one or more of;

a position, a velocity, and time for the antenna.

21. The system of claim 14, wherein operation (iii) is performed without input from a Phase Locked Loop (PLL) and wherein the matched subspace detector is further operable to:

(iv) identify, for each of the selected wireless signals, a corresponding set of interfering signals, wherein a first wireless signal has a first set of interfering signals, wherein a second wireless signal has a second set of interfering signals, wherein the memberships of the first and second sets are different, wherein the first and second sets are created after each of the selected wireless signals has been acquired and tracked, wherein the acquiring and tracking comprises obtaining, as at least part of the corresponding signal modeling data, two or more of a pseudo-random number, code offset data, Doppler data, code offset rate, and Doppler rate, and wherein the identification of a signal as an interfering signal is based on threshold criteria that includes at least one of;

(a) a predetermined number of the strongest of said corresponding signals, (b) a predetermined decibel increase above a predetermined value, (c) a signal-to-noise ratio, (d) a signal-to-carrier ratio, (e) a carrier-to-noise ratio, (f) a relative amplitude, and (g) a weighted sum of two or more of (a) through (f).

22. The system of claim 14, wherein the matched subspace detector constructs a reference signal from the signal modeling data for so, the reference signal being used to determine said interference subspace, wherein the interference subspace is complex, wherein the reference signal for so has the following representation:

s_o=sI₀+i*sQ₀

wherein the reference signal for s₀ is composed of a real component sI₀, which is a column vector containing the in-phase component, and a complex component i*sQ₀, where i=sqrt(−

1) and sQ₀, which is a column vector containing the quadrature component.

23. The system of claim 14, wherein each of the signal models is complex and wherein the selected wireless signals have unequal powers and wherein the acquiring operation comprises the sub-operations of:

tracking and acquiring the wireless signal h₀ having a first power; and

identifying each of the plurality of wireless signals having a power greater than the first magnitude as an interferer and those having a power less than the first magnitude as a noninterferer;

wherein in the projecting operation the at least one interfering signal (s₀) comprises only the signals identified as interferers.

24. The system of claim 15, wherein each of the signal models is complex and wherein the selected wireless signals have unequal powers and wherein the obtaining operation comprises the suboperations of:

tracking and acquiring at least some of the plurality of selected wireless signals;

grouping the tracked and acquired selected wireless signals based on the relative powers of the signals; and

for each ungrouped selected wireless signal, performing the projecting operation, wherein the at least one interfering signal (s₀) comprises the grouped selected wireless signals;

wherein the acquiring operation is performed for each ungrouped selected wireless signal.

25. The system of claim 15, wherein the signal modeling data of each selected wireless signal comprises estimates of time offset, a Doppler data, and a signal frequency and not of phase, wherein the representation of the signal h_O is characterized by a respective signal model and wherein the model represents the in phase and quadrature components of the signal h_O.

29. The signal processing system of claim 14, wherein operation (iii) removes substantially all interfering wireless signals from known interfering signaling sources from the composite signal y to permit acquisition of signal ho.

27. A signal processing method, comprising:

(a) an antenna receiving a composite signal (y), wherein y includes, from each of a plurality of signaling sources, at least one corresponding wireless signal comprising information;

(b) obtaining, for each selected wireless signal in the composite signal, signal modeling data, the respective model for each selected wireless signal comprises both a real component and a complex component and excludes a phase estimate;

(c) based on the signal modeling data for each selected wireless signal, determining a respective model, each respective model containing both in phase and quadrature components of the corresponding selected wireless signal;

(d) performing a projection of a representation of y onto a detection subspace to remove all of at least one interfering wireless signal (s₀) from at least one known interfering signaling source, the detection subspace being orthogonal to a complex interference subspace spanning a representation of the at least one interfering signal s₀ of the corresponding wireless signals, wherein said interference subspace is determined using said respective signal modeling data for the at least one interfering signal s₀ and wherein said detection subspace is non-orthogonal and non-equivalent to a signal-of-interest subspace spanning a representation of another signal (h_O) of said corresponding wireless signals, wherein step (d) is performed without estimating a phase of one or more of the selected wireless signals and wherein the complex interference subspace in step (d) is multiplied by a complex conjugate;

(e) using a result from said step of performing for acquiring said another corresponding signal h_O; and

(f) after acquiring the signal h_O, determining the information from the signal h_O.

30. The signal processing method of claim 27, wherein step (d) removes substantially all interfering wireless signals from known interfering signaling sources from the composite signal y to permit acquisition of signal h_O.