A new family of MMSE multiuser receivers for interference suppression in DS/CDMA systems employing BPSK modulation

In this paper, we deal with interference suppression in asynchronous direct -sequence code-division multiple-access (CDMA) systems employing binary pha se-shift keying modulation. Such an interference may arise from other users of the network, from external low-rate systems, as well as from a CDMA net work coexisting with the primary network to form a dual-rate network. We de rive, for all of these cases, a new family of minimum mean-square-error det ectors, which differ from their conventional counterparts in that they mini mize a modified cost function. Since the resulting structure is not impleme ntable with acceptable complexity, we also propose some suboptimum systems. The statistical analysis reveals that both the optimum and the suboptimum receivers are near-far resistant, not only with respect to the other users, but also with respect to the external interference. We also present a blin d and a recursive least squares-based, decision-directed implementation of the receivers wherein only the signature and the timing of the user to be d ecoded and the signaling time and the frequency offset of the external inte rferer are assumed known. Finally; computer simulations show that the propo sed adaptive algorithm outperforms the classical decision-directed RLS algo rithm.