Noncoherent sequential acquisition of PN sequences for DS/SS communications with/without channel fading

Studies sequential acquisition schemes of m-sequences, based on the sequential probability ratio test (SPRT) and a truncated SPRT (TSPRT), with noncoherent demodulation. Most reported results on sequential acquisition schemes assume that independent samples are available for the decision process. The assumption of independent and identically distributed (i.i.d.) samples requires the integrator in the receiver to be reset periodically. This introduces loss in the effective signal-to-noise ratio, degrading the performance. In the present paper, on the contrary, the authors´ two sequential schemes use continuous integration. It can be shown that the likelihood ratio is monotonic; consequently, the tests can be easily implemented in realtime. Methods are proposed for designing the decision thresholds to achieve the desired false-alarm and miss probabilities. Performances of the proposed schemes are obtained and they suggest that the TSPRT is more desirable. The effect of slowly-varying channel fading is also investigated. Results show that fading does not affect the false alarm probabilities, but it can drastically reduce the probability of detecting the alignment of the two PN sequences, especially when the fading is severe.<>