Effect of Adaptive Array Processing on GPS Signal Crosscorrelation
October 2004
Ronald L. Fante, The MITRE Corporation
Michael P. Fitzgibbons, The MITRE Corporation
Keith F. McDonald, The MITRE Corporation
ABSTRACT
Adaptive space-time arrays can be used to cancel jammers interfering with GPS receiver operation. However, there is a concern that the adaptive filter used for jammer cancellation can distort the GPS signal crosscorrelation function, especially if a non-constrained jammer cancellation algorithm, such as power minimization, is used. We have examined this issue via both experimentation and simulation. The experiments were conducted using a seven-channel linear array that has five adaptive time taps per channel. A jammer waveform is injected into each channel, thus, simulating a broadside jammer minus antenna effects. When a power minimization algorithm was used for jammer cancellation, it was found that significant distortion of the crosscorrelation function would be encountered for signals incident on the array from a significant portion of the upper hemisphere around the jammer location. Simulations confirmed these results. Simulations alone were then used to assess the performance of a CRPA with 11 adaptive time taps/element. Strong jammers were placed on the horizon and the crosscorrelation function calculated for various angular locations of GPS satellites. It was found that for this configuration and with 11 adaptive time taps/element (rather than only 5) the crosscorrelation distortion was not as severe, and significant errors were confined to a relatively small solid angle around the location of each jammer.
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