  Communications in dispersive direct-sequence code-division multiple-access
(DS-CDMA) channels suffer from intersymbol and multiple-access interference,
which can significantly impair performance. Joint maximum \textit{a posteriori}
probability (MAP) equalization and multiuser detection with error control
decoding can be used to mitigate this interference and to achieve the optimal
bit error rate. Unfortunately, such optimal detection typically requires
prohibitive computational complexity. This problem is addressed in this paper
through the development of a reduced state trellis search detection algorithm,
based on decision feedback from channel decoders. The performance of this
algorithm is analyzed in the large-system limit. This analysis and simulations
show that this low-complexity algorithm can obtain near-optimal performance
under moderate signal-to-noise ratio and attains larger system load capacity
than parallel interference cancellation.
