JOINT SIGNAL-DETECTION AND PARAMETER-ESTIMATION IN MULTIUSER COMMUNICATIONS

This paper considers the problem of simultaneously detecting the information bits and estimating signal amplitudes and phases in a K-user asynchronous direct-sequence spread-spectrum multiple-access communication system. The joint maximum-likelihood (ML) estimator has a computational complexity that is exponential in the total number of bits transmitted, and thus does not represent a practical solution to the problem. We consider an estimator that combines a suboptimum tree-search algorithm with a recursive least-squares estimator of complex signal amplitude. The complexity of this estimator is O(K2) computations per decoded bit, and its performance is very close to that of the joint ML receiver. This receiver has the advantage that the transmitted signal powers and phases are extracted from the received signal in an adaptive fashion without using a test sequence.