Performance of Sequential Probability Ratio Test for GPS Acquisition

Acquisition of signals in noise, in particular CDMA signals like the Global Positioning System (GPS) L1 C/A signal, can be carried out using fixed or variable dwell times. In this work, a sequential multiple dwell procedure for verifying acquisition is examined and compared to a fixed time single dwell strategy. The procedure under analysis is the sequential probability ratio test (SPRT) which has not been widely used for GPS applications, possibly due to its sensitivity to attenuation of the received signal relative to the design point. In this paper, it is shown that for the received signal to noise ratios (SNR) typically encountered in GPS, the SPRT can outperform the single dwell detector strategy in terms of mean acquisition time. In addition, it is shown that the single dwell (SD) detector's fixed dwell time approaches the worst case dwell time for the SPRT, as design point carrier to noise ratio decreases. Thus, for very weak signals, the SPRT can be a better choice of verification algorithm than the SD strategy, under certain constraints.