Fourier-transform-based adaptive radio interference mitigation

• US 6,166,678 A
• Filed: 09/07/1999
• Issued: 12/26/2000
• Est. Priority Date: 09/07/1999
• Status: Expired due to Fees

• Current Assignee: United States Air Force
• Original Assignee: United States Of America As Represented By The Secretary Of The Air Force
• Inventors: Jao, Jen King
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US09/389,734
• Time in Patent Office: 476 Days
• Field of Search: 342/25, 342/89, 342/91, 342/92, 342/93, 342/98, 342/99, 342/102, 342/151, 342/152, 342/159, 342/161, 342/162, 342/192, 342/194, 342/195, 342/196
• US Class Current: 342/25.00A
• CPC Class Codes: G01S 13/90 using synthetic aperture techniques , e.g. synthetic aperture radar [SAR] techniques
• CPC Class Codes: G01S 7/023 Interference mitigation, e.g. reducing or avoiding non-intentional interference with other HF-transmitters, base station transmitters for mobile communication or other radar systems, e.g. using electro-magnetic interference [EMI] reduction techniques auxiliary means for detecting or identifying radar signals or the like G01S7/021; means for anti-jamming G01S7/36
• CPC Class Codes: G01S 7/2926 by integration
• CPC Class Codes: G01S 7/36 Means for anti-jamming , e.g. ECCM, i.e. electronic counter-counter measures

Abstract

A signal process is provided for radar interference mitigation in SAR data and to perform several functions. Initially, the algorithm separately removes the average range bias of the I-channel and the Q-channel data. Next, I- and Q-channels are equalized by properly compensating their phase difference and gain imbalance due to either constant or random timing jitters. The current implementation well compensates relative I/Q timing jitters within two sampling time intervals which, for the FOPEN III receiver, are 4 nanoseconds. Graceful performance degradation of the algorithm is expected when timing jitter exceeds two sampling intervals. For example, phase jitter on the order of 5 sampling intervals will be partially but not perfectly corrected. Following the I/Q equalization, adaptive RFI rejection is performed. The FOPEN III data bandwidth may also be reduced 50% with hardly any information loss. The operation is allowed principally because of over-sampling; the FOPEN III A/D rate of 500 MHz exceeds the receiver bandwidth of 200 MHz by more than a factor of 2.

Claims

1. A process for mitigating interference from inphase (I) and quadrature (Q) radar data comprising the steps of:

taking interference samples from pre-nadir radar data;

subtracting an interference estimate from the I and Q radar data;

wherein the interference estimate is obtained as a spectral weighting function W(f) from the interference sampler averaged over N pulse intervals.

2. A process for mitigating interference from in phase (I) and quadrature (Q) radar data comprising the steps of:

an I/Q equalization step to estimate phase timing jitters between sets of I and Q radar data;

phase compensating an I/Q channel spectrum S(W) of the quadrature radar data to obtain a phase compensated data spectrum using;

space="preserve" listing-type="equation">S(ω

)=S.sub.l (ω

)+exp(-jω

τ

)S.sub.Q (ω

).