Multiuser reception for trellis-based code division multiple access communications

A code division multiple access (CDMA) system is considered where a trellis-based encoding scheme provides the direct-sequence spread-spectrum modulator with a signature sequence chosen from a bi-orthogonal set. A number of detectors are considered that maximize the likelihood ratio. In addition to the optimum multiuser receiver with very high computational complexity, we present schemes based on a reduced tree search algorithm and a multistage detector. The numerical results show the gain in performance compared to the uncoded transmission and indicate as well the capability of alleviating the near-far problem for all three detectors