A detector based on calculation of a posteriori probability is proposed for code acquisition in singleuser direct sequence code division multiple access (DS/CDMA) systems. Available information is used for decision making, unlike conventional methods which only use a part of it. Although this increases the overhead in terms of additional memory and computational complexity, significant performance improvements are achieved. The frame work is extended to multiuser systems and again mean acquisition time/correct acquisition probability performance is superior to the conventional systems although computational complexity is high. An approximate multiuser method with significantly less complexity is also derived.

We propose a post-filter (digital filter applied after the correlator) to reduce multiple-access interference (MAI) in the correlator output in asynchronous communications. Optimum filter coefficients are derived for Markov and i.i.d. codes. It is shown that post-filter is not needed for Markov case. Variance of MAI is reduced in i.i.d. codes and it becomes equal to that of Markov codes; thus, both will have the same bit error rate (BER) performance. This post-filter reduces level of MAI in the correlator output for Gold codes as well.