Timing Acquisition for Multi-User IDMA

Abstract

Acquisition of the timing in an IDMA system must take place before signal detection and decoding are performed. Acquisition in the presence of severe multiple-access interference with time varying codes makes the task even more difficult. Inefficient designs cause a large number of false alarms and/or missed detections. This paper applies a powerful acquisition technique to IDMA systems in the uplink. Under high multiple access interference conditions conventional acquisition techniques used for DS-CDMA systems simply fail. The proposed method utilises soft data from the iterative IDMA receiver to effectively cancel interference from the co-channel users. Analytical performance in terms of the number of users, spreading gain, performance of the IDMA receiver, and noise variance is developed, together with simulation results.