Computationally efficient multiuser detection for coded CDMA

Computationally efficient multiuser detection for coded asynchronous CDMA systems is investigated. The particular receiver studied is a near-far resistant multiuser detector known as the projection receiver (PR). The PR performs multiple access interference resolution for CDMA with error control coding. The output of the front-end of the projection receiver yields a metric for decoding of the coded sequences. This metric allows the use of a standard sequence decoder (e.g., Viterbi algorithm, M-algorithm) for the error control code. The metric computation can be performed adaptively by an extension of the familiar recursive least-squares (RLS) algorithm. The adaptive PR operates on a single sample per chip. It is shown that for random spreading codes this algorithm simplifies and can be executed an order of magnitude faster by exploiting the average cross-correlation of the spreading sequences. The performance of both algorithms are studied for CDMA with random spreading sequences and compared to theoretical performance bounds