Return link code acquisition with DS-CDMA for high capacity multiuser systems under realistic conditions

Acquisition of the code timing in a direct-sequence code-division multiple-access system at the base station must take place before signal detection and decoding is possible. Code acquisition under severe multiple access interference conditions with time varying codes makes the task even more difficult. Inefficient designs lead to large number of false alarms and/or missed detections. This paper details a realistic powerful code acquisition technique for the uplink of direct-sequence code-division multiple-access systems under high loaded situations, where the number of users is greater than the processing gain. Under this high multiple access interference condition the DS-CDMA acquisition problem becomes very difficult and conventional search methods simply fail. The method discussed utilises soft data from a multiuser detector to reduce the interference received by the acquisition unit. Numerical results validate performance under realistic conditions with amplitude, phase and frequency impairments.