Multiuser detection for asynchronous CDMA using block coordinate ascent and semi-definite relaxation

Maximum-likelihood (ML) multiuser detection provides attractive bit error rate performance, but it is computationally prohibitive to implement (except in certain restricted cases). Recently, it has been shown that ML detection for synchronous CDMA can be efficiently and accurately approximated using the semi-definite relaxation (SDR) method. In this work, we consider the application of SDR to the more general scenario of asynchronous CDMA. To make this application computationally feasible, we incorporate a block coordinate ascent (BCA) technique into our detector. Simulation studies show that the resulting BCA-SDR detector has significantly better BER performance than several typical suboptimal multiuser detectors.