Direct sequence spread spectrum receiver and antenna array for the simultaneous formation of a beam on a signal source and a null on an interfering jammer

• US 5,694,416 A
• Filed: 02/24/1995
• Issued: 12/02/1997
• Est. Priority Date: 02/24/1995
• Status: Expired due to Fees

• Current Assignee: Radix Technologies, Inc. (The Boeing Co.)
• Original Assignee: Radix Technologies, Inc. (The Boeing Co.)
• Inventors: Johnson, Russell K.
• Primary Examiner(s): Bocure, Vesfaldet
• Assistant Examiner(s): WEBSTER, BRYAN E
• Application Number:
  US08/393,716
• Time in Patent Office: 1,012 Days
• Field of Search: 375/200, 375/202, 375/206, 375/207, 375/208, 375/316, 375/317, 375/346, 375/348, 375/349, 375/350, 375/280, 375/267, 375/347, 342/359, 342/361, 342/362, 342/368, 342/378, 455/132, 455/137
• US Class Current: 375/148
• CPC Class Codes: H04B 1/126 having multiple inputs, e.g. auxiliary antenna for receiving interfering signal aerials in general H01Q
• CPC Class Codes: H04B 7/08 at the receiving station
• CPC Class Codes: H04L 1/06 using space diversity

Abstract

A navigation satellite receiver that nulls interference and enhances satellite signals using differences in their spatial positions and that includes four antennas in a spatial array respectively connected to four amplitude and phase balanced receiver downconverter channels. Five satellite tracking channels are each connected to all four receiver channels and each includes despreaders and I/Q accumulators for early, late and punctual correlation. The despreader and accumulator combinations provide four-by-one vectors called aperture estimates. A code-gated maximum likelihood processor whitens these by multiplication with the mathematical inverse Cholesky factor of the interference data. This vector is generated in a millisecond block "k" and is multiplied by a similarly generated vector formed in a previous millisecond block "k-1". The magnitude of the resulting product is used for code tracking, and the phase of the result provides for carrier tracking.

Claims

1. A radio receiver for simultaneously hulling out an interference signal and enhancing a signal-of-interest that differ at least in their azimuth and/or elevation relative to the receiver, comprising:

an antenna array with "N" number of individual antennas spatially distributed at random and providing for the reception of said interference signal and said signal-of-interest, wherein a first phase difference in the carrier frequency of said interference signal exists between any two antennas that is substantially different than a second phase difference in the carrier frequency of said signal-of-interest for said same two antennas;

multi-channel receiver down-conversion means connected to respective antennas in the antenna array; and

combining means connected to the multi-channel receiver down-conversion means for simultaneously hulling out said interference signal and enhancing said signal-of-interest based on said first and second carrier frequency phase differences;

wherein, said interference is determined to be a jammer from a set of pre-despread spatial correlation measurements and that provide for an interference autocorrelation estimate;

the combining means provides for the use of said interference autocorrelation estimate to remove said interference from a post-despread aperture vector, and which leaves only a strong signal-of-interest; and

wherein, the antenna array is adaptive and provides for simultaneous maximization of a signal-of-interest and a minimization of both narrowband and wideband jamming interference from a variety of directions that can vary in real-time by providing for an adjustment of a plurality of direct sequence spread spectrum (DSSS) local code phases once a code and a code phase lock have been achieved to effectively aim an antenna-array-reception-pattern null in a direction of a jammer.

2. The receiver of claim 1, wherein:

the antenna array provides for the reception of L-band microwave radio transmissions from orbiting navigation satellites as said signal-of-interest and said interference signal includes transmissions from a jammer;

wherein, copies the GPS space vehicles based on the vector correlation with the GPS code for that space vehicle (SV).

3. A radio receiver for simultaneously nulling out an interference signal and enhancing a signal-of-interest that differ at least in their azimuth and/or elevation relative to the receiver, comprising:

an antenna array with individual antennas spatially distributed and providing for the reception of said interference signal and said signal-of-interest, wherein a first phase difference in the carrier frequency of said interference signal exists between any two antennas that is substantially different than a second phase difference in the carrier frequency of said signal-of-interest for said same two antennas;

multi-channel receiver down-conversion means connected to respective antennas in the antenna array;

combining means connected to the multi-channel receiver down-conversion means for simultaneously nulling out said interference signal and enhancing said signal-of-interest based on said first and second carrier frequency phase differences;

the antenna array provides for the reception of L-band microwave radio transmissions from orbiting navigation satellites as said signal-of-interest and said interference signal includes transmissions from a jammer;

the multi-channel receiver down-conversion means provides for code and carrier tracking of direct sequence spread spectrum (DSSS) types of transmissions in said L-band microwave radio transmissions;

the combining means includes aperture estimate formation means including in-phase (I) and quadrature (Q) despreaders and accumulators for early, late and puntual correlation of said DSSS transmissions, wherein said despreaders and accumulators provide for a continuous output of aperture estimates; and

the combining means further comprises a code-gated maximum-likelihood (CGML) processor connected to the multi-channel receiver down-conversion means for whitening said aperture estimates with means for taking an inverse Cholesky factor of a pre-despread interference data, wherein the magnitude of a resulting products provide for code tracking and the phase of the result provides for carrier tracking.

4. The receiver of claim 3, further comprising:

a navigation processor connected to the CGML processor and providing for three-dimensional position solutions in the presence of severe interference from said jammer.

5. The receiver of claim 3, further comprising:

an aperture processor connected to receive said aperture estimates and the CGML processor and providing for the generation of focusing matrices and a focusing of said aperture estimates by a multiplying a respective one of said focusing matrices and interference data vectors, wherein the combining means is provided with data for simultaneously nulling-out said interference signal and enhancing said signal-of-interest based on said first and second carrier frequency phase differences when the antenna array is rolling and/or tumbling relative to said signal sources.

6. A navigation satellite receiver for hulling-out interference and enhancing satellite signals by using differences in the spatial positions of the signal sources, comprising:

a plurality of antennas in a spatial array providing for the reception of L-band microwave radio transmissions from orbiting navigation satellites and subject to interference from jammers;

a plurality of amplitude-balanced and phase-balanced receiver downconverter channels one each respectively connected to individual ones of the plurality of antennas;

a plurality of satellite tracking channels each one connected to every one of the plurality of receiver channels and each including in-phase (I) and quadrature (Q) despreaders and accumulators for early, late and punctual correlation, wherein said despreaders and accumulators provide four-by-one vectors as aperture estimates; and

a code-gated maximum likelihood (CGML) processor connected to the satellite tracking channels for voltage-domain whitening of said aperture estimates by an inverse Cholesky factor of a pre-despread interference data, wherein the magnitude of a resulting product provides information for code tracking and the phase of the result provides information for carrier tracking.

7. The receiver of claim 6, further comprising:

a navigation processor connected to the CGML processor and providing for three-dimensional position solutions in the presence of severe interference from said jammers.

8. The receiver of claim 6, further comprising:

an aperture focusing processor connected to the plurality of satellite tracking channels and providing for an aperture focusing process to find a linear mapping (M_e) that transforms a spatial interference correlation at a start of a block "k" to match a spatial interference correlation matrix collected at a start of a subsequent block "k+1", wherein subapertures collected over an interval are focused by multiplication with linear interpolations of a focusing matrix.

9. The receiver of claim 8, wherein:

the aperture focusing processor is connected to receive on-time, early and late sub-aperture vectors periodically from each of a plurality of satellite tracking channels and corresponding interference data vectors from an interference estimator, and connected to output a plurality of sub-aperture focusing matrices, to focus sub-aperture vectors by multiplication by an appropriate focusing matrix, and focus a plurality of interference data vectors.

10. The receiver of claim 9, wherein:

the aperture focusing processor is further connected to output on-time, early and late sub-aperture vectors and interference data vectors, for each satellite being tracked, each millisecond to the CGML processor, wherein a computed Cholesky factor of an interference data from a block "k" is stored in preparation for a next block computation, and said focusing matrices are computed after first computing both a Cholesky factor of a current received interference data as well as its inverse.

11. The receiver of claim 6, further comprising:

a navigation processor connected to receive the magnitude and phase of a plurality of CGML detection statistics from the CGML processor for code and carrier phase locking and providing for three-dimensional position solutions in the presence of severe interference from said jammers; and

an aperture focusing processor connected to the plurality of satellite tracking channels and providing for an aperture focusing process to find a linear mapping (M_e) that transforms a spatial interference correlation at a start of a block "k" to match a spatial interference correlation matrix collected at a start of a subsequent block "k+1" that periodically outputs to the CGML processor a plurality of on-time, early and late focused subapertures, wherein subapertures collected over an interval are focused by multiplication with linear interpolations of a focusing matrix.

12. The receiver of claim 6, wherein:

the CGML processor is connected to generate a magnitude and a phase of a plurality of early, late and on-time modified CGML detection statistics each millisecond for each satellite being tracked, and the magnitude and phase of each of said detection statistics is provided to the navigation processor for code and carrier phase tracking purposes, wherein the CGML processor estimates an inverse interference auto-correlation matrix each millisecond.

13. The receiver of claim 12, wherein:

the CGML processor includes means for receiving a plurality of on-time, early and late focused sub-apertures from the aperture focusing processor 202 and for adding them together to form a plurality of focused aperture estimates that are then mathematically whitened in the voltage domain by an inverse Cholesky factor of an interference data, wherein the inner product of a CGML vector from a current millisecond period update block is formed with a corresponding CGML vector from a previous update block.