A sub-optimum MLSE detector with a folded state-transition trellis preselection stage

The maximum-likelihood sequence estimation (MLSE) multiuser detector has a very good performance but at the expense of the exponentially increasing number of states with the number of users. A scheme that folds up the original trellis to reduce the number of states involved has been proposed by Sim and Cruickshank (see Proceedings of the 1999 49th IEEE Vehicular Technology Conference, p.846-50, 1999). In this paper, the folded trellis detector is combined with the MLSE. The main idea here is to use the folded trellis which has a linear complexity to preselect a subset of the bit-combinations and then apply the MLSE to this much smaller set.