GPS receiver interference nuller with no satellite signal distortion

• US 6,480,151 B2
• Filed: 12/28/2001
• Issued: 11/12/2002
• Est. Priority Date: 12/29/2000
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Al-Dhahir, Naofal, Ashe, Jeffrey M., Maalouf, Khalil J.
• Primary Examiner(s): Phan, Dao
• Application Number:
  US10/035,676
• Publication Number:
  US 20020122002A1
• Time in Patent Office: 319 Days
• Field of Search: 342/357.02, 342/357.06, 342/357.12, 455/63, 455/65, 455/67.3
• US Class Current: 342/357.59
• CPC Class Codes: H04L 1/06 using space diversity
• CPC Class Codes: H04L 2025/03509 fractionally spaced H04L2025/03515 takes precedence
• CPC Class Codes: H04L 25/03044 using fractionally spaced delay lines or combinations of fractionally integrally spaced taps

Abstract

Interference in a GPS receiver in minimized while preserving the GPS satellite signal in a system having N antenna elements for receiving the interference signal and the satellite signal and multiple tapped delay line structures connected to the antenna elements for filtering the signals received by the antenna elements based a plurality of filter coefficients. The filter coefficients are determined such that the plurality of filter coefficients equals R_{{tilde over (xx)}}⁻¹C[C^HR_{{tilde over (xx)}}⁻¹C]⁻¹F wherein C^H{tilde over (w)}=F, where {tilde over (w)} equals the plurality of filter coefficients, R_{{tilde over (xx)}} equals a covariance matrix, and C and F are determined to preserve a frequency spectrum of the GPS satellite signal.

Claims

1. A method for minimizing an effect of at least one interference signal while minimizing the distortion of at least one GPS satellite signal, the method comprising the steps of:

receiving the at least one interference signal and the at least one GPS satellite signal by a plurality of antenna elements and processing the received signals; and

filtering the received processed signals by a plurality of multiple tapped delay line structures based a plurality of filter coefficients,

whereby the plurality of filter coefficients equals R_{{tilde over (xx)}}<sup>−

1</sup>C[C^HR_{{tilde over (xx)}}<sup>−

1</sup>C]<sup>−

1</sup>F wherein C^H{tilde over (w)}=F, where {tilde over (w)} equals the plurality of filter coefficients, R_{{tilde over (xx)}} equals a covariance matrix, and C and F are determined to preserve a frequency spectrum of the at least one GPS satellite signal.

2. The method of claim 1 wherein C and F are determined based on a condition that $c_m=\sum _{}^{}$

n=1N

wn

 



m*



-jΔ

n

 



for

 



m=1,…



 



M,

where c_m corresponds to coefficients of an FIR filter and are determined to preserve the frequency spectrum of the at least one GPS satellite signal and where M equals a number of taps of each plurality of multiple tapped delay line structures, N equals a number of the plurality of antenna elements, Δ

_n equals a carrier frequency multiplied by a time delay at an n-th antenna element relative to a first antenna element of the plurality of antenna elements, and w_nm equals an m-th filter coefficient for a multiple tapped delay line structure connected to an n-th antenna element.

3. The method of claim 2 wherein at least one of c₁, c₂, . . . , c_M, is equal to one and a remainder of c₁, c₂, . . . , c_M, is equal to zero.

4. The method of claim 2, wherein c_m is determined based on a frequency response of the processed satellite signal.

5. The method of claim 1, wherein C and F are determined based on a condition that $g_i=\sum _{}^{}$

n=1N

∑

m=1M

wn

 



m*



-jΔ

n



-j

ω

~i

τ

n



j

ω

~i

kTs

for at least one frequency component, {tilde over (ω

)}_i, of the at least one GPS satellite signal, where T_s equals a sampling rate and τ

_n equals an inter-element time delay at an n-th antenna element.

6. The method of claim 1 comprises the further steps of:

determining whether each received process signal is a valid signal; and

disregarding each invalid received processed signal when determining the plurality of filter coefficients and filtering the received processed signals.

7. The method of claim 1, wherein an update period for determining the covariance matrix is based on stationary characteristics of the received processed signals.

8. An apparatus for minimizing an effect at least one interference signal while minimizing the distortion of at least one GPS satellite signal, the apparatus comprising:

a plurality of antenna elements for receiving the at least one interference signal and the at least one GPS satellite signal;

a plurality of multiple tapped delay line structures operatively connected to the plurality of antenna elements for filtering the signals received by the plurality of antenna elements, respectively, wherein each of the plurality of multiple tapped delay line structures filters the signals based a plurality of filter coefficients; and

a processor for computing the plurality of filter coefficients for each of the plurality of multiple tapped delay line structure to preserve a frequency spectrum of the at least one GPS satellite signal, wherein the plurality of filter coefficients equals R_{{tilde over (xx)}}<sup>−

1</sup>C[C^HR_{{tilde over (xx)}}<sup>−

1</sup>C]<sup>−

1</sup>F wherein C^H{tilde over (w)}=F, where {tilde over (w)} equals the plurality of filter coefficients and R_{{tilde over (xx)}} equals a covariance matrix, and C and F are determined to preserve a frequency spectrum of the at least one GPS satellite signal.

9. The apparatus of claim 8, wherein the processor determines C and F based on a condition that $c_m=\sum _{}^{}$

n=1N

wn

 



m*



-jΔ

n

 



for

 



m=1,…



 



M,

where c_m corresponds to coefficients of an FIR filter and are determined to preserve the frequency spectrum of the at least one GPS satellite signal and where M equals a number of taps of each plurality of multiple tapped delay line structures, N equals a number of the plurality of antenna elements, Δ

_n equals a carrier frequency multiplied by a time delay at an n-th antenna element relative to a first antenna element of the plurality of antenna elements, and w_nm equals an m-th filter coefficient for a multiple tapped delay line structure connected to an n-th antenna element.

10. The apparatus of claim 9 wherein the processor sets at least one of c₁, c₂, . . . , c_M, equal to one and a remainder of c₁, c₂, . . . , c_M, equal to zero.

11. The apparatus of claim 9, wherein the processor determines c_m based on a frequency response of the processed satellite signal.

12. The apparatus of claim 8, wherein the processor determines C and F based on a condition that $g_i=\sum _{}^{}$

n=1N

∑

m=1M

wn

 



m*



-jΔ

n



-j

ω

~i

τ

n



j

ω

~i

kTs

for at least one frequency component, {tilde over (ω

)}_i, of the at least one GPS satellite signal, where T_s equals a sampling rate and τ

_n equals an inter-element time delay at an n-th antenna element.

13. The apparatus of claim 8 further comprising:

an invalid signal tracker for determining whether each received process signal is a valid signal.

14. The apparatus of claim 8, wherein the processor updates the covariance matrix based on stationary characteristics of the received processed signals.

15. A computer-readable medium on which is stored a set of instructions for minimizing an effect of at least one interference signal while minimizing the distortion of at least one GPS satellite signal wherein a plurality of antenna elements receive the at least one interference signal and the at least one GPS satellite signal and a plurality of multiple tapped delay line structures operatively connected to the plurality of antenna elements filter the signals received by the plurality of antenna elements, respectively, and each of the plurality of multiple tapped delay line structures filters the signals based a plurality of filter coefficients, which when the set of instructions are executed performs the step comprising:

determining the plurality of filter coefficients such that the plurality of filter coefficients equals R_{{tilde over (xx)}}<sup>−

1</sup>C[C^HR_{{tilde over (xx)}}<sup>−

1</sup>C]<sup>−

1</sup>F wherein C^H{tilde over (w)}=F, where {tilde over (w)} equals the plurality of filter coefficients, R_{{tilde over (xx)}} equals a covariance matrix, and C and F are determined to preserve a frequency spectrum of the at least one GPS satellite signal.

16. A computer-readable medium of claim 15, wherein C and F are determined based on a condition that $c_m=\sum _{}^{}$

n=1N

wn

 



m*



-jΔ

n

 



for

 



m=1,…



 



M,

for m=1, . . . M, where c_m corresponds to coefficients of an FIR filter and are determined to preserve the frequency spectrum of the at least one GPS satellite signal and where M equals a number of taps of each plurality of multiple tapped delay line structures, N equals a number of the plurality of antenna elements, Δ

_n equals a carrier frequency multiplied by a time delay at an n-th antenna element relative to a first antenna element of the plurality of antenna elements, and w_nm equals an m-th filter coefficient for a multiple tapped delay line structure connected to an n-th antenna element.

17. The computer-readable medium of claim 16 wherein at least one of c₁, c₂, . . . , c_M, is equal to one and a remainder of c₁, c₂, . . . , c_M, is equal to zero.

18. The computer-readable medium of claim 16, wherein c_m is determined based on a frequency response of the processed satellite signal.

19. The computer-readable medium of claim 15, wherein C and F are determined based on a condition that $g_i=\sum _{}^{}$

n=1N

∑

m=1M

wn

 



m*



-jΔ

n



-j

ω

~i

τ

n



j

ω

~i

kTs

for at least one frequency component, {tilde over (ω

)}_i, of the at least one GPS satellite signal, where T_s equals a sampling rate and τ

_n equals an inter-element time delay at an n-th antenna element.

20. The computer-readable medium of claim 15, wherein the set of instructions further execute the step comprising:

determining whether each received process signal is a valid signal; and

disregarding each invalid received processed signal when determining the plurality of filter coefficients and filtering the received processed signals.

21. The computer-readable medium of claim 15, wherein the covariance matrix is updated based on stationary characteristics of the received processed signals.