Coded Asynchronous Near-Far Resistant DS-CDMA Receivers Operating Without Synchronization

In this paper, several receivers for data demodulation in an asynchronous direct-sequence code-division multiple access (DS-CDMA) system operating without prior knowledge of the propagation delays are proposed and compared. Special attention is paid to the near-far problem, and the proposed schemes are numerically shown to be near-far robust. The near-far robustness is obtained by estimating the a priori unknown propagation delay using a subspace-based technique. Quantities obtained in the estimation procedure are subsequently used to design an interference suppression filter according to the minimum mean-squared error criterion. A simple two-state Viterbi algorithm is used for the data demodulation in the uncoded case. By extending the trellis used in the Viterbi algorithm, error correcting coding is easily implemented. I. Introduction The so-called near-far problem in a DS-CDMA system occurs when the received signals from different users are nonorthogonal and have dissimilar powers,..