Adaptive spatial temporal selective attenuator with restored phase

Abstract

An adaptive attenuator is provided, the adaptive attenuator including at least two sensor ports. Each of the sensor ports receives an input signal that includes data on a first channel and a reference sequence on a second channel. One or more delay ports is coupled to each sensor port for receiving the input signal, and a computational port is coupled to the sensor ports and the delay ports. The computational port receives the input signal and the output of the delay ports and performs one or more computations to produce a processed signal which is substantially free of interference. A phase restorer receives the processed signal and the reference sequence and restores phase to the processed signal in accordance with the reference sequence.

Description

[0001] The present application claims priority from U.S. Provisional Applications Serial Nos. 60/387,697 and 60/387,701 both of which are hereby incorporated herein, in their entirety by reference.

TECHNICAL FIELD

[0002] The present invention relates to wireless signaling systems, and more particularly to apparatuses and methods for providing an adaptive temporal selective attenuator with restored phase.

BACKGROUND ART

[0003] The vulnerability of a Global Positioning System ("GPS") signal to various types of interference is well known. Any interference signal near the band of the GPS signal can saturate the GPS receiver and, at the same time, deteriorate the auto-correlation properties of the GPS signal and its PRN code. This results in loss of lock on the GPS signal. This type of near band interference is common in pseudo-satellite, or pseudolite, systems in which the emitters are in close proximity to each other and to the pseudolite receiver. This situation is common when pseudolites are used in ground-based, indoor or underground positioning systems.

[0004] Interference from nearby pseudolites may be reduced by using a phased array antenna to reduce the amplitude of signals from directions other than that of the desired signal. However such antenna systems introduce a distortion to signal received from the desired pseudolite (which typically transmits a GPS-type of signal). The need for, restoring the phase of a combined signal coming out of the phased array when processing is performed in a time domain is not new. For example, the Extended Replica Folding Acquisition Search Technique ("XFAST") exploits the cross-correlation property of the code waveforms in such a way that the entire time uncertainty interval can be searched simultaneously. XFAST performs the processing in the frequency domain, which makes it less susceptible to time delay and phase distortion introduced by jamming suppression insertion.

[0005] Another approach appears to improve the receiver's tracking loop to handle high dynamic stress and radio frequency interference ("RFI") conditions. This technique, known as the FLL-assisted-PLL provides, under RFI conditions, both the dynamic robustness due to FLL and the performance accuracy due to PLL. Nevertheless, there exists a limitation to this approach because of the saturation of the receiver due to powerful interference sources or hostile jammers.

[0006] An example of the use of an adaptive spatial temporal selective attenuator has been discussed by Progri and Michalson in "Adaptive Spatial and Temporal Selective Attenuator in the Presence of Mutual Coupling and Channel Errors" presented at the Institute of Navigation (ION GPS 2000, Sep. 19-22 2000, Salt Lake City, Utah, pp. 462-470). This publication and presentation are incorporated herein, in their entirety, by reference.

SUMMARY OF THE INVENTION

[0007] In accordance with one embodiment of the present invention, an adaptive attenuator includes at least two sensor ports. Each of the sensor ports receives an input signal that includes data on a first channel and a reference sequence on a second channel. One or more delay ports is coupled to each sensor port for receiving the input signal, and a computational port is coupled to the sensor ports and the delay ports. The computational port receives the input signal and the output of the delay ports and performs one or more computations to produce a processed signal that is substantially free of interference. A phase restorer receives the processed signal and the reference sequence and restores phase to the processed signal in accordance with the reference sequence. In accordance with a related embodiment, the sensor ports may include an antenna. In accordance with a further related embodiment, the computation port may include a processor. The first channel may be a quadrature-phase channel. Similarly, the first channel may be an in-phase channel.

[0008] In accordance with another embodiment of the invention, a system for transmitting substantially interference-free data in a geolocation system includes at least two sensor ports. Each of the sensor ports receives an input signal, and the input signal includes data on a first channel and a reference sequence on a second channel. One or more delay ports is coupled to each sensor port for receiving the input signal, and a computational port is coupled to the sensor ports and the delay ports. The computational port receives the input signal and the output of the delay ports and performs one or more computations to produce a processed signal that is substantially free of interference. A phase restorer coupled to the computational port receives the processed signal and the reference sequence and restores phase to the processed signal in accordance with the reference sequence. A receiver coupled to the phase restorer receives the output of the phase restorer and the processed signal and reads the data. In accordance with a related embodiment, the data may be read in synchrony with the reference sequence. In accordance with a further related embodiment, the computation port may include a processor. In accordance with yet another related embodiment, the first channel may be a quadrature-phase channel. Additionally, the first channel may be an in-phase channel.

[0009] In accordance with a further embodiment of the invention, a method for mitigating interference in a geolocation system includes sensing an input signal at two or more sensor ports. The input signal includes data on a first channel and a reference sequence on a second channel. The input signal is delayed on one or more delay ports, and one or more computations is performed on the input signal and the output of the delay ports to produce a processed signal which is substantially free of interference. Phase is restored to the processed signal in accordance with the reference sequence. In accordance with a related embodiment, data is read from the processed signal in synchrony with the reference sequence. Reading data from the processed signal in accordance with the reference signal or in synchrony with the reference signal may include using a detection criterion or other detection means for data bit transition. Reading data from the processed signal in synchrony with the reference sequence may include using an auto-correlation function peak of the processed signal as the detection criterion for data bit transition. Reading data from the processed signal in accordance with the reference may further include signal cross-correlating with reference sequence to yield data bit transition.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The foregoing features of the invention will be more readily understood by reference to the following detailed description, taken with reference to the accompanying drawings, in which:

[0011] FIG. 1 is a block diagram illustrating an adaptive spatial temporal selective attenuator with restored phase in accordance with an embodiment of the invention;

[0012] FIG. 2 is a block diagram illustrating a system for transmitting substantially interference-free data in a geolocation system in accordance with another embodiment of the invention;

[0013] FIG. 3 is a flowchart illustrating a method for mitigating interference in a geolocation system; and

[0014] FIG. 4 is a flow chart illustrating a method for mitigating interference in a geolocation system in accordance with a further embodiment of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0015] The present invention provides users with the ability mitigate narrowband, wideband and wideband pseudorandom noise interference. Such interference may be caused either as a result of unintentional, in-band interference or intentional jamming. By employing the apparatuses and methods of the invention, users may track a desired GPS or GPS-like signal in such environments. Applications of the embodiments of the invention include, but are not limited to aviation, ground transportation, military mobile units, indoor navigation and underground navigation.

[0016] FIG. 1 is a block diagram illustrating an adaptive spatial temporal selective attenuator with restored phase in accordance with an embodiment of the invention. The attenuator 100 utilizes a plurality of antenna or sensor ports to provide a plurality of spatial degrees of freedom and may use a plurality of temporal shifter delays to provide a plurality of temporal degrees of freedom.

[0017] As shown in FIG. 1, the attenuator 100 includes a computation port 105, which may be a processor and at least two sensor ports 101. The attenuator 100 also includes one or more temporal shifter delays or delay ports 102. The total input signal received by one sensor port is the sum of an input signal and an interference signal. The input signal may be a coded signal with data only on one channel. The data may be transmitted on either an in-phase channel or a quadrature-phase channel. A second channel (the channel without data) is then used as a reference channel. The reference signal channel contains one or more known pseudo-random related sequences 103.

[0018] The computational port 105 receives the input signal and the output of the delay ports 102 and performs one or more computations to produce a processed signal that is substantially free of interference. For example, cross-correlating the reference sequences 103 with the total received signal vector yields the desired pointing vector. Moreover, cross-correlating the total received signal (desired input signal and interference signal) with its Hermitian transpose matrix produces an auto-correlation matrix. A desired set of multipliers 104 may be obtained by the inner product of the inverse of the auto-correlation matrix with the pointing vector.

[0019] The processed signal produced by the computational port 105 is received by a phase restorer 106. The phase restorer 106 computes the processed signal as the inner product of the Hermitian transpose of the desired set of multipliers 104 with the total received signal vector. The phase restorer 106 also exploits the reference sequences 103 from the reference signal channel to restore the phase of the processed signal from the computational port 105.

[0020] FIG. 2 is a block diagram illustrating a system for transmitting substantially interference-free data in a geolocation system in accordance with another embodiment of the invention. The system of FIG. 2 may be used in a geolocation system such as the geolocation system disclosed in co-pending application entitled "Reconfigurable Indoor Geolocation System" filed on the same day as the present application (Jun. 11, 2003) and bearing attorney docket number 2627/103 which is incorporated herein by reference.

[0021] In accordance with the embodiment of FIG. 2, a system 200 for transmitting substantially interference-free data includes at least two sensor ports 201. Each of the sensor ports 201 receives an input signal, and the input signal includes data on a first channel and a reference sequence 203 on a second channel. One or more delay ports 202 is coupled to each sensor port 201 for receiving the input signal, and a computational port 205 is coupled to the sensor ports and the delay ports. As in FIG. 1, each of the sensor ports 201 may include an antenna, and the computation port 205 may include a processor or other computational device. The computational port 205 receives the input signal as well as the output of the delay ports 202 and performs one or more computations (such as those described with respect to the computation port 105 of FIG. 1) to produce a processed signal that is substantially free of interference. A phase restorer 206 coupled to the computational port 205 receives the processed signal and the reference sequence 203 and restores phase to the processed signal in accordance with the reference sequence 203. A receiver 207 coupled to the phase restorer 206 receives the output of the phase restorer as well as the processed signal and reads the data.

[0022] The receiver 207 may read the data in accordance with the reference sequence 203 in two ways. First, if the input signal contains only one known pseudo-random reference sequence on the second channel, then the auto-correlation function peak of the processed signal (produced by the computation port 205) is used as the detection criterion for data bit transition. If the input signal contains two known pseudo-random or pseudo-random related sequences, then the processed signal may be cross-correlated with the second pseudo-random sequence to yield the data bit transition.

[0023] If the desired signal structure and sampling frequency are known, the number of antenna or sensor ports, the element geometry, and the number of delay ports may be selected to yield optimum system performance. Further, algorithms such as recursive Cholesky and modified Graham Schmid orthogonalization ("MGSO") may be employed to produce fast and efficient computation of the desired set of multipliers. (For further discussion regarding recursive Cholesky and modified Graham Schmid orthogonalization see "A Comparison Between the Recursive Cholesky and MGSO Algorithms" presented by Progri et al. at the Institute of Navigation (ION NTM 2002, Jan. 28-30 2002, San Diego, Calif., pp. 655-665). This publication and presentation are hereby incorporated herein, in their entirety, by reference.)

[0024] FIG. 3 is a flowchart illustrating a method for mitigating interference in a geolocation system. In process 301, an input signal is sensed at two or more sensor ports or antenna elements. The input signal includes data on a first channel and a reference sequence on a second channel. The input signal is delayed 302 on one or more delay ports, and one or more computations is performed 303 on the input signal and the output of the delay ports at computational port. The computational port produces a processed signal which is substantially free of interference and phase is restored 304 to the processed signal in accordance with the reference sequence.

[0025] FIG. 4 is a flow chart illustrating a method for mitigating interference in a geolocation system in accordance with a further embodiment of the invention. In accordance with this embodiment an input signal is sensed 401 at two or more sensor ports. As above, the input signal includes data on a first channel and a reference sequence on a second channel. The input signal is delayed 402 on one or more delay ports, and one or more computations is performed 403 on the input signal and the output of the delay ports at computational port. The computational port produces a processed signal which is substantially free of interference and phase is restored 404 to the processed signal in accordance with the reference sequence. If the input signal contains only one known pseudo-random reference sequence on the second channel, then the auto-correlation function peak of the processed signal is used 405 as the detection criterion for data bit transition. If the input signal contains two known pseudo-random or pseudo-random related sequences, then the processed signal is cross-correlated 406 with the second pseudo-random sequence to yield the data bit transition. The data is then read 407 by the receiver. Other detection techniques, such as blind source detection, which are known in the art, may be substituted for using auto-correlation or cross-correlation to detect data bit transitions.

[0026] Further disclosure relating to adaptive spatial and temporal selective attenuation may be found in "An Investigation of the Adaptive Temporal Selective Attenuator" presented by Progri et al. at the Institute of Navigation (ION GPS, 2001, Sep. 11-14 2001, Salt Lake City, Utah., pp. 1952-1960), "An Investigation of the Adaptive Spatial Temporal Selective Attenuator" presented by Progri and Michalson at the Institute of Navigation (ION GPS, 2001, 11-14 September, Salt Lake City Utah., pp. 1985-1996), "An Investigation of a GPS Adaptive Temporal Selective Attenuator" (Progri et al. NAVIGATION, Journal of the Institute of Navigation, Vol. 49, No. 3, Fall 2002, pp. 137-147) and "An Improved Adaptive Spatial Temporal Selective Attenuator" also presented by Progri and Michalson at the Institute of Navigation (ION GPS, 2001, Sep. 11-14 2001, Salt Lake City, Utah., pp. 932-938). All of the above referenced publications and presentations are hereby incorporated herein, in their entirety, by reference.

[0027] While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification. This application is intended to cover any variation, uses, or adaptations of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which invention pertains.

Claims

What is claimed is:

1. An adaptive attenuator comprising: at least two sensor ports, each of the sensor ports receiving an input signal, the input signal including data on a first channel and a reference sequence on a second channel; one or more delay ports coupled to each sensor port for receiving the input signal; a computational port coupled to the sensor ports and the delay ports, the computational port receiving the input signal and the output of the delay ports and performing one or more computations to produce a processed signal which is substantially free of interference; and a phase restorer for receiving the processed signal and the reference sequence and restoring phase to the processed signal in accordance with the reference sequence.

2. An attenuator according to claim 1, wherein the sensor ports include an antenna.

3. An attenuator according to claim 1, wherein the computation port includes a processor.

4. An attenuator according to claim 1, wherein the first channel is a quadrature-phase channel.

5. An attenuator according to claim 1, wherein the first channel is an in-phase channel.

6. A system for transmitting interference-free data in a geolocation system, the system comprising: at least two sensor ports, each of the sensor ports receiving an input signal, the input signal including data on a first channel and a reference sequence on a second channel; one or more delay ports coupled to each sensor port for receiving the input signal; a computational port coupled to the sensor ports and the delay ports, the computational port receiving the input signal and the output of the delay ports and performing one or more computations to produce a processed signal which is substantially free of interference; a phase restorer for receiving the processed signal and the reference sequence; and restoring phase to the processed signal in accordance with the reference sequence; and a receiver for receiving the output of the phase restorer and the processed signal and reading the data.

7. A system according to claim 6, wherein the data is synchronized with the reference sequence.

8. A system according to claim 6, wherein the sensor ports include an antenna.

9. A system according to claim 6, wherein the computation port includes a processor.

10. A system according to claim 6, wherein the first channel is a quadrature-phase channel.

11. A system according to claim 6, wherein the first channel is an in-phase channel.

12. A method for mitigating interference in a geolocation system, the method comprising: sensing an input signal at two or more sensor ports, the input signal including data on a first channel and a reference sequence on a second channel; delaying the input signal at one or more delay ports; performing one or more computations on the input signal and the output of the delay ports to produce a processed signal which is substantially free of interference; and restoring phase to the processed signal in accordance with the reference sequence.

13. A method according to claim 12, further comprising: reading data from the processed signal in accordance with the reference sequence.

14. A method according to claim 13, wherein reading data from the processed signal includes reading data in synchrony with the reference signal.

15. A method according to claim 14, wherein reading data from the processed signal includes using a detection criterion for data bit transition.

16. A method according to claim 13, wherein reading data from the processed signal includes using a detection criterion for data bit transition.

17. A method according to claim 14, wherein reading data from the processed signal in synchrony with the reference sequence includes using an auto-correlation function peak for detecting for data bit transition.

18. A method according to claim 14, wherein reading data from the processed signal in synchrony with the reference sequence includes cross-correlating the signal with the reference sequence to detect data bit transition.

19. A method according to either of claims 13, wherein reading data from the processed signal in accordance with the reference signal includes using detection means to detect data bit transition.

20. A method according to either of claims 14, wherein reading data from the processed signal in accordance with the reference signal includes using detection means to detect data bit transition.