INTERFERENCE CANCELLATION SYSTEM

• US 20130309975A1
• Filed: 05/21/2013
• Published: 11/21/2013
• Est. Priority Date: 05/21/2012
• Status: Active Grant

• Current Assignee: Bascom Hunter Technologies, Inc., L3 Technologies, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Inventors: Kpodzo, Elias Bonaventure, Holland, Robert, Deng, Yanhua, Prucnal, Paul, McCandless, Andrew, Dourbal, Paul
• Granted Patent: US 9,444,502 B2
• Time in Patent Office: Days
• US Class Current: 455/63.1
• CPC Class Codes: H04B 1/10 Means associated with receiver for limiting or suppressing noise or interference
• CPC Class Codes: H04B 1/1027 assessing signal quality or detecting noise/interference for the received signal
• CPC Class Codes: H04B 1/109 by improving strong signal performance of the receiver when strong unwanted signals are present at the receiver input
• CPC Class Codes: H04B 10/00 Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
• CPC Class Codes: H04B 10/07955 Monitoring or measuring power
• CPC Class Codes: H04B 10/2507 for the reduction or elimination of distortion or dispersion
• CPC Class Codes: H04B 10/2575 Radio-over-fibre, e.g. radio frequency signal modulated onto an optical carrier
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04B 17/336 Signal-to-interference ratio [SIR] or carrier-to-interference ratio [CIR]
• CPC Class Codes: H04B 2210/006 Devices for generating or processing an RF signal by optical means
• CPC Class Codes: H04K 3/20 Countermeasures against jamming in radar G01S7/36; interference suppression in receivers H04B1/10
• CPC Class Codes: H04K 3/228 Elimination in the received signal of jamming or of data corrupted by jamming interference suppression in receivers H04B1/10
• CPC Class Codes: H04L 43/16 Threshold monitoring

Abstract

Systems and methods for cancelling interference from a received signal in order to properly detect a signal of interest are disclosed. 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, for example based on a detected output power of an optical subsystem of the interference cancellation system. 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.

Claims

1. An interference cancellation system (ICS), the ICS comprising:

a radio frequency (RF) subsystem configured to receive a first signal corresponding to an interferer signal and a second signal corresponding a combination of the interferer signal and a signal of interest (SOI);

an optical subsystem configured to;

receive the first signal and the second signal from the RF subsystem,

variably attenuate and variably time delay one or more of the first signal and the second signal based on one or more control signals received from a digital subsystem,

combine the first signal and the second signal into a combined signal after variably attenuating and variably time delaying one or more of the first signal and the second signal; and

the digital subsystem configured to;

generate the control signals based on a power level associated with the combined signal output from the optical subsystem, and

send the control signals to the optical subsystem.

2. The ICS of claim 1, wherein the RF subsystem comprises an RF correlator configured to receive the combined signal and provide an indication of the power level associated with the combined signal to the digital subsystem.

3. The ICS of claim 2, wherein the RF subsystem further comprises an RF frequency detector configured to receive a signal transmitted by a radio transceiver and send an indication of frequency associated with the signal transmitted by the radio transceiver to the digital subsystem.

4. The ICS of claim 3, wherein the RF correlator and the RF frequency detector share one or more synthesizers that are configured to tune the RF correlator to the frequency associated with the signal transmitted by the radio transceiver.

5. The ICS of claim 1, wherein the RF subsystem further comprises a transmit power level detector configured to receive a signal transmitted by a radio transceiver and provide an indication of a power level associated with the signal transmitted by the radio transceiver to the digital subsystem.

6. The ICS of claim 5, wherein the digital subsystem is configured to determine to route the signal transmitted by the radio transceiver to an antenna based on the power level associated with the signal transmitted by the radio transceiver being above a predetermined threshold.

7. The ICS of claim 6, wherein the digital subsystem is configured to determine to route a signal received via the antenna to optical subsystem based on the power level associated with the signal transmitted by the radio transceiver being below the predetermined threshold.

8. The ICS of claim 1, wherein the optical subsystem comprises a plurality of optical processing lines and each of the optical processing lines are configured to attempt to cancel a different multipath signal associated with a transmitted version of the interferer signal.

9. The ICS of claim 1, wherein the optical subsystem is configured to convert one or more of the first signal or the second signal from an RF signal to an optical signal using a direct modulation technique.

10. The ICS of claim 1, wherein the digital subsystem is configured to generate the control signals in order to attempt to minimize the power level associated with the combined signal output from the optical subsystem.

11. The ICS of claim 10, wherein the digital subsystem is configured to generate the control signals in order to attempt to minimize the power level associated with the combined signal output from the optical subsystem using a two variable minimization method and the two variables that are varied in order to minimize the power level associated with the combined signal output from the optical subsystem comprise an attenuation level applied by the optical subsystem and a time delay applied by the optical subsystem.

12. The ICS of claim 1, wherein the RF subsystem comprises one or more equalizers configured to compensate for non-linear channel effects associated with a channel traversed by a transmitted version of the interferer signal.

13. The ICS of claim 1, wherein the optical subsystem is configured to apply a time delay to the second signal using a plurality of fiber optic delay lines included between paired wavelength division multiplexing (WDM) units.

14. The ICS of claim 13, wherein the optical subsystem comprises a plurality of tunable continuous wave (CW) lasers and the plurality of tunable CW lasers are configured to control which of the plurality of fiber optic delay lines are utilized at a given instance in time.

15. The ICS of claim 13, wherein a first tunable CW laser of the plurality of tunable CW lasers is configured to be active at a given instance and a second tunable CW laser of the plurality of tunable CW lasers is configured to tune to a frequency associated with a non-active fiber optic delay line while the first tunable CW laser is active.

16. A method for attempting to cancel an interference signal from a combined interference and signal of interest (SOI) signal, the method comprising:

receiving a first radio frequency (RF) signal corresponding to the interference signal and a second RF signal corresponding to the combined interference and SOI signal;

converting the first RF signal to a first optical signal and the second RF signal to a second optical signal and applying a 180 degree phase shift to one of the first optical signal or the second optical signal before, during, or after optical conversion;

optically attenuating and optically time delaying the first optical signal;

combining the attenuated and time delayed first optical signal with the second optical signal to create a combined optical signal;

converting the combined optical signal to a combined RF signal;

sending the combined RF signal to a radio transceiver, wherein optically attenuating and optically time delaying the first optical signal is performed in order to minimize a power level associated with the combined RF signal.

17. The method of claim 16, further comprising applying an RF time delay to the first RF signal prior to convert the first RF signal to the first optical signal, wherein the RF time delay is at least an order of magnitude larger than an optical time delay that is applied to the first optical signal.

18. The method of claim 16, further comprising determining one or more initial optical attenuation values or optical delay values to be applied to the first optical signal based on determining that a power difference between a signal associated with the interference signal and a signal associated with the combined interference and SOI signal.

19. The method of claim 16, further comprising:

determining when an interferer is transmitting the interferer signal and when the radio transceiver is transmitting a transmission signal;

determining to perform interference cancellation when the interferer is transmitting and the radio transmitter is not transmitting; and

determining to refrain from performing interference cancellation when the interferer is not transmitting or when the radio transceiver is not transmitting.

20. The method of claim 16, wherein combining the attenuated and time delay first optical signal with the second optical signal to create a combined optical signal results in at least 50 dB of cancellation of the interference signal from the combined interference and SOI signal.