Iterative timing recovery for IDMA receivers operating under severe timing drift

Recently interleaved division multiple access (IDMA) has been proposed as an enhancement for 3GPP wireless broadband standards. Timing synchronisation in an IDMA system must take place in conjunction with signal detection and decoding. This paper compares an iterative timing recovery technique with a conventional timing recovery approach for IDMA systems in the uplink. Under high multiple access interference and very severe timing drift conventional timing recovery techniques have been shown to result in poor performance. In conventional multi-user DS/CDMA systems the pilot channel is used exclusively for single-shot timing synchronisation. In this paper we propose an iterative timing synchronisation algorithm which uses soft data channel to aid the synchronisation process. MMSE combining is used to determine the optimal timing error discriminator.Decoded information from the previous iteration is used to cancel interference from the co-channel users before timing recovery is performed on each iteration. Under severe drift scenarios, our results show that the new algorithm developed reduces the timing error variance by a factor of 15 times and, consequently results in a 2 dB gain in bit-error rate at high SNR as compared with conventional techniques.