Flexible GPS Receiver for Jammer Detection, Characterization and Mitigation Using a 3D CRPA

D. Wilson, S. Ganguly

Abstract:	Anti-Jam (A/J) receivers use a variety of methods in attempting to obtain increased operational abilities in interference-laden environments. Spatial processing methods are often paired with temporal and frequency domain methods in order to provide all-encompassing interference rejection. Spatial processing methods are often accomplished through the use of multiple element antenna structures which provide the capability of real-time beam- and nullsteering able to adapt to the dynamic environment. In wide use are 7 element planar controlled reception pattern antennas (CRPAs), which suffer from an inherent difficulty. All planar sensor arrays have the characteristic that the beamwidth varies with scan angle, particularly detrimental for several reasons. One solution to this is the use of a conformal spherical array which is able to provide direction-independent angular resolution. The development of such an antenna structure is presented along with full-wave numerical EM code (NEC)simulation results which demonstrate its operation. Most A/J receivers in addition resort to frequency and temporal domain mitigation efforts. Frequency domain mitigation methods include frequency excision, in which narrowband interference power is reduced without degradation to the GPS signal. Temporal domain methods often include the use of tapped delay line (TDL) filters following each antenna element. These timedomain structures attempt to provide resistance to delayed replicas of both the GPS and interference signals. When paired with spatial domain methods, the incorporation of TDL structures is referred to as Space-Time Adaptive Processing (STAP). STAP has been recently demonstrated as an improvement over previously used methods, and with the advent of modern processors, the computational expense can be brought to the level of real-time operation. An implementation of the STAP algorithm using a DFT is presented, as well as the advantages to using this method. Methods for increasing the real-time throughput are also discussed. The development of a software receiver for interference characterization and mitigation is presented here. Both pre- and post- correlation techniques are presented, and the advantages to the use of both are discussed. Simulation results demonstrate the use of our conformal 3D CRPA in providing lower variance direction-of-arrival (DOA) estimates than that previously obtained using a planar CRPA. The interference mitigation algorithms are presented, and it is shown that lower variance DOA estimates supplement constrained beamforming techniques to provide enhanced operation in the face of both intentional and unintentional interference.
Published in:	Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006) September 26 - 29, 2006 Fort Worth Convention Center Fort Worth, TX
Pages:	189 - 200
Cite this article:	Wilson, D., Ganguly, S., "Flexible GPS Receiver for Jammer Detection, Characterization and Mitigation Using a 3D CRPA," Proceedings of the 19th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2006), Fort Worth, TX, September 2006, pp. 189-200.
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