GPS receiver search techniques

GPS receivers must perform a two-dimensional sequential search process for the GPS signals. The two-dimensional search pattern consists of discrete search cells with each cell representing one code bin and one carrier Doppler bin. The code bin width is usually 1/2 -half chip. The longer the dwell time per binary decision (the predetection integration time), the narrower the Doppler bin width and weaker GPS signals can be acquired, but the search time increases. The replica C/A-code generates larger than normal sidelobes if the Doppler bin is too wide (when predetection integration time is too short), False acquisition of the sidelobes can occur if the search threshold is set too low. At the heart of the receiver search process is the search detector. There are significant performance differences between search detector algorithms. This paper describes, analyzes and compares two powerful sequential search algorithms: the fixed-dwell-time M-of-N detector and the variable dwell time Tong detector (1973).