Decoder-aided synchronization for multiuser CDMA systems

This paper addresses the problem of frame synchronization in code division multiple access systems in the presence of high multiple access interference. Already acquired user signals are regenerated using soft information from the respective decoders and subtracted from the received signal to mitigate multiple access interference. We consider partial cancellation of interference after few decoder iterations for fast acquisition of remaining weak users. Hence the effect of residual interference after cancellation is considered in the derivation of the time offset estimator. We consider both data-aided and non-data-aided scenarios. Our approach uses linear pre-processing (whitening filter) on the interference cancelled signal for further performance improvement. Analytical expressions for the missed detection probability of a given user are derived. These analytical results are verified via Monte-Carlo simulations. We compare conventional code acquisition to our whitening filter method within the parallel interference cancellation framework.