On the use of interference suppression to enhance acquisition performance in a CDMA overlay scenario

The coarse acquisition performance of the mobile-to-base station link of a CDMA overlay system for mobile radio is presented. Specifically, a direct sequence spread spectrum CDMA system, supporting communication between mobile units and a base station, is overlaid in frequency on a single narrowband BPSK user. At the CDMA base-station receivers, narrowband interference rejection filters are used to suppress the BPSK interference. It is demonstrated that the presence of the BPSK interference does not severely affect the acquisition performance when the ratio of BPSK bandwidth to CDMA bandwidth is small. As the ratio becomes larger, the acquisition performance degrades, but the use of the interference rejection filter still significantly decreases the time to acquire. We also demonstrate that severe performance degradation results when there is flat Rayleigh fading, both with and without an overlay. When there is a line-of-sight component, of course, performance is much better.