Cross correlation mitigation techniques for software GPS C/A code receivers

Abstract

The cross correlation properties of the 1023 chip Gold (C/A) codes can cause difficulties in scenarios where both strong and weak GPS signals need to be processed. Such cases are increasingly likely given the new applications of GPS, with examples being the processing of GPS signals in E911 cellular phone applications and the use of bistatic GPS as a remote sensing tool. This coupled with the increasing use of software-defined radio (software correlation) for either cost-saving or flexibility enhancing reasons have resulted in a need to mitigate cross correlations within such systems. This paper provides details on two techniques developed by the authors for the mitigation of GPS cross correlations, both of which have been tested and implemented within a software correlator that has been written in the C programming language. Details on the software correlator are also provided as the table lookup requirements for the correlator are smaller than those previously reported. Test results indicating the effectiveness of the algorithms are presented, with a comparison between the two methods being performed., The datasets containing cross correlations were obtained by capturing the output of a GPS radio front end chip attached to a hardware GPS simulator.