Simulation performance of a quantized log-likelihood sequential detector for PN code acquisition in the presence of data modulation and Doppler shift

The problem of initial acquisition of data modulated spread-spectrum PN codes in low signal-to-noise ratio (SNR) conditions using a variable-dwell time serial search synchronizer controlled by a sequential detector is addressed. The effect of carrier and code rate Doppler frequency offsets on the acquisition characteristics of three kinds of sequential detector was assessed by means of a Monte Carlo computer simulation, and their performances were compared. The detectors examined are: the ideal log-likelihood sequential detector; the quantized log-likelihood sequential detector; and the biased square law sequential detector. These were analyzed in the presence of Doppler shift and data modulation at two values of bias, namely, the normalized Wald´s (1947) optimum bias and a nonoptimum bias