An iterative detector for asynchronous spread-spectrum multiple-access systems

Proposes and analyzes an iterative multiuser detector for coherent demodulation in an asynchronous spread spectrum multiple access (SSMA) system. This detector processes the sufficient statistics using an iterative algorithm which is based on a multiple access interference annihilation strategy. An efficient real-time implementation of the iterative algorithm with a fixed decoding delay is obtained. This implementation requires a computational complexity per symbol which is linear in the number of users. An exact probability of error analysis shows that even the two-stage detector is particularly well suited for near-far situations. Its performance approaches that of single-user communications as the interfering signals become stronger. It is shown that significant performance gains over the conventional detector are obtained for relatively high bandwidth efficiency situations