Suppressing QPSK DS/CDMA interference

Three adaptive QPSK direct-sequence code-division multiple-access (DS/CDMA) receivers for suppressing QPSK DS/CDMA interference are introduced. Performance results for the three proposed receivers, as well as results for the linear correlation receiver, are provided. In particular, we consider their performance in a four user, 255 chip QPSK DS/CDMA system. The proposed receivers are compared to each other, and also to the linear correlation receiver, in terms of signal-to-noise ratio (including multiple-access noise) and computational complexity. We demonstrate that for most practical scenarios, with our receivers, decision-directed suppression can be used throughout transmission, including at the beginning of transmission, and during transmission, as near-far interferers gain access to the system. Furthermore, the receivers are shown to successfully suppress near-far multiple-access interference without requiring knowledge of other users spreading codes, timing or phase information