INTERFEINTERFENCE CANCELLATION SYSTEM FOR LOCATION AND DIRECTION FINDING

• US 20140218240A1
• Filed: 02/07/2014
• Published: 08/07/2014
• Est. Priority Date: 02/07/2013
• Status: Active Grant

• Current Assignee: L3 Technologies, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Kpodzo, Elias Bonaventure, Holland, Robert
• Granted Patent: US 9,651,652 B2
• Time in Patent Office: Days
• US Class Current: 342/450
• CPC Class Codes: G01S 19/21 Interference related issues ; Issues related to cross-correlation, spoofing or other methods of denial of service
• CPC Class Codes: G01S 3/043 Receivers
• CPC Class Codes: G01S 5/0215 Interference

Abstract

Systems and methods for cancelling interference while performing direction/location. A combined signal of interest plus interference signal may be received. A copy or sample of the interference signal may be determined. The interference signal and the combined signal of interest plus interference signal may be converted to the optical domain. The interference signal may be optically phase shifted by −180 degrees, which may result in an optically inverted interference signal. The optically inverted interference signal may be variably optically attenuated and/or variably optically time delayed. As a result, interference cancellation of the interference signal from the combined signal of interest plus interference signal may be achieved, resulting in 50 dB or more of cancellation of the interference signal. Direction and/or location finding techniques can be applied to received signals during and/or after interference cancellation.

Claims

1. A method for determining a relative direction of a signal of interest (SOI) under interference conditions, the method comprising:

receiving a plurality of radio frequency (RF) signals via an antenna array, wherein each respective RF signal of the plurality of RF signals is received via a respective antenna element of the antenna array, and each respective RF signal comprises a respective instance of an RF SOI and a respective instance of an RF interfering signal;

determining a sample of the RF interfering signal;

converting each of the plurality of RF signals to a plurality of optical signals, and converting the sample of the RF interfering signal to an optical interfering signal;

applying a 180 phase shift to the optical interfering signal;

variably attenuating and variably time delaying the optical interfering signal;

combining an instance of the optical interfering signal with each of the plurality of optical signals after variably attenuating and variably time delaying the optical interfering signal;

converting the plurality of optical signals to a second plurality of RF signals after combining the optical interfering signal with each of the plurality of interfering signals; and

estimating a relative direction to the RF SOI based on a physical configuration of the antenna array and one or more of the relative amplitudes of the second plurality of RF signals, the relative timing differences of the second plurality of RF signals, or the relative phase differences of the second plurality of RF signals.

2. The method as in claim 1, wherein the optical interfering signal is individually variably attenuated and individually variably time delayed for each of the plurality optical signals.

3. The method as in claim 2, wherein the individual variable attenuation and the individual variable time delay applied to a respective instance of the optical interference signal to be combined with a respective optical signal is determined based on a resulting output power level of a respective RF signal of the second plurality of RF signals that corresponds to the respective optical signal.

4. The method as in claim 1, wherein estimating the relative direction to the RF SOI is performed using triangulation or trilateration.

5. The method as in claim 1, further comprising determining an estimated position of a transmitter of the RF SOI based on the estimated relative direction of the RF SOI and a known or estimated transmission power of the transmitter of the RF SOI.

6. A direction finding system comprising:

a radio frequency (RF) subsystem comprising an antenna array, wherein the antenna array comprises a plurality of respective antenna elements, and the RF subsystem is configured to;

receive a plurality of RF signals via the antenna array, wherein each respective RF signal of the plurality of RF signals is received via a respective antenna element of the antenna array, and each respective RF signal comprises a respective instance of an RF SOI and a respective instance of an RF interfering signal,

determine the RF interfering signal, and

send the RF interference signal and at least one of the plurality of RF signals to an optical subsystem;

the optical subsystem configured to;

convert the at least one of the plurality of RF signals to at least one optical signal,

convert the RF interfering signal to an optical interfering signal,

apply a 180 phase shift to the optical interfering signal,

variably attenuate and variably time delay the optical interfering signal,

combine an instance of the optical interfering signal with the at least one optical signal after variably attenuating and variably time delaying the optical interfering signal, and

convert the at least one optical signal to at least one interference cancelled RF signal after combining the optical interfering signal with each of the plurality of interfering signals; and

a digital subsystem configured to estimate a relative direction to the RF SOI based on a physical configuration of the antenna array and one or more an amplitude of the at least one interference cancelled RF signal, a timing of the at least one interference cancelled RF signal, or a phase of the at least one interference cancelled RF signal.

7. The direction finding system as in claim 6, wherein the RF subsystem further comprises:

at least one phase detector configured to determine relative phase difference between the plurality of RF signals received via the antenna array; and

at least one RF correlator configured to adjust a signal provided to the digital subsystem for determining the relative direction of the RF SOI based on one or more of the relative phase differences determined by the at least one phase detector and one or more of the plurality of RF signals received via the antenna array.

8. The direction finding system as in claim 6, wherein each antenna element of the antenna array is a directional antenna, and the digital subsystem is configured to use the relative directionality of the plurality of directional antennas and relative power levels of the second plurality of RF signals to estimate the relative direction of the RF SOI.

9. The direction finding system as in claim 6, wherein the RF interfering signal is transmitted by a jamming device directly coupled to the direction finding system.

10. The direction finding system as in claim 6, further comprising an interference estimation (IEP) processor and IEP antenna coupled to the IEP processor, wherein the IEP antenna comprises a directional antenna configured to maximize reception in a direction of a transmitter of the RF interfering signal, and the IEP processor is configured to determine the RF interfering signal based on a IEP signal received via the IEP antenna.

11. A method for determining a position of a device experiencing interference, the method comprising:

receiving a plurality of radio frequency (RF) signals from a plurality of transmitters each located at a known position, wherein each respective RF signal of the plurality of RF signals is transmitted from one of the transmitters, and each respective RF signal comprises a respective RF SOI and a respective instance of at least one RF interfering signal;

determining a sample of the at least one RF interfering signal;

converting each of the plurality of RF signals to a plurality of optical signals, and converting the sample of the at least one RF interfering signal to at least one optical interfering signal;

applying a 180 phase shift to the at least one optical interfering signal;

variably attenuating and variably time delaying the at least one optical interfering signal;

combining an instance of the at least one optical interfering signal with each of the plurality of optical signals after variably attenuating and variably time delaying the at least one optical interfering signal;

converting the plurality of optical signals to a second plurality of RF signals after combining the at least one optical interfering signal with each of the plurality of interfering signals; and

estimating a current position based on the known positions of each of the transmitters and one or more of the relative amplitudes of the second plurality of RF signals, the relative timing differences of the second plurality of RF signals, or the relative phase differences of the second plurality of RF signals.

12. The method as in claim 11, wherein estimating the current position comprises performing trilateration using the second plurality of RF signals.

13. The method as in claim 11, wherein estimating the current position comprises performing triangulation using the second plurality of RF signals.

14. The method as in claim 11, wherein at least one interfering signal comprises a plurality of separate interfering signals.

15. The method as in claim 14, wherein one of the plurality of separate interfering signals is determined based on directly sampling a first interfering signal and another of the plurality of separate interfering signals is determined based on estimating a second interfering signal using a directional antenna.

16. A location determining system comprising:

a radio frequency subsystem configured to;

receive a plurality of radio frequency (RF) signals from a plurality of transmitters each located at a known position, wherein each respective RF signal of the plurality of RF signals is transmitted from one of the transmitters, and each respective RF signal comprises a respective RF SOI and a respective instance of an RF interfering signal,

determining a sample of the RF interfering signal, and

send the RF interfering signal and each of the plurality of RF signals to an optical subsystem;

the optical subsystem configured to;

convert each of the plurality of RF signals to a plurality of optical signals,

convert the sample of the RF interfering signal to an optical interfering signal,

apply a 180 phase shift to the optical interfering signal,

variably attenuate and variably time delay the optical interfering signal,

combine an instance of the optical interfering signal with each of the plurality of optical signals after variably attenuating and variably time delaying the optical interfering signal, and

convert the plurality of optical signals to a second plurality of RF signals after combining the optical interfering signal with each of the plurality of interfering signals; and

a digital subsystem configured to estimate a current position based on the known positions of each of the transmitters and one or more of the relative amplitudes of the second plurality of RF signals, the relative timing differences of the second plurality of RF signals, or the relative phase differences of the second plurality of RF signals.

17. The location determining system as in claim 16, wherein one or more of the plurality of transmitters is located at a respective global positioning system (GPS) satellite.

18. The location determining system as in claim 17, wherein at least one of the plurality of transmitters is located at fixed location that is not a satellite and the RF signal corresponding to the at least one of the plurality of transmitters is used as an error correction signal for correcting a position determination that was based on one or more signals transmitted from GPS satellites.

19. The location determining system as in claim 16, wherein one or more of the plurality of transmitters is located at a cellular base station.

20. The location determining system as in claim 16, wherein the digital system is configured to individually control the attenuation and time delay applied in the optical subsystem for each of the plurality of optical signals.