This paper studies the performance of a coded convolutional spreading CDMA system with cyclic prefix (CS-CDMA/CP) combined with the zero correlation zone code generated from the M-sequence (M-ZCZ code) for downlink transmission over a multipath fast fading channel. In particular, we propose a new pilot-aided channel estimation scheme based on the shift property of the M-ZCZ code and show the robustness of the scheme against fast fading through comparison with the W-CDMA system empolying time-multiplexed pilot signals.

We investigated the suppression of multiuser interference in uplink multicarrier CDMA systems using the minimum mean squared error combining (MMSEC) method. In MMSEC, many pilot symbols are required to converge the weight vectors, and if we use just a few pilot symbols, the performance cannot be improved very much. We therefore developed a method for calculating weight vectors for MMSEC that uses just a few pilot symbols. The impulse responses of all users are first estimated using the pilot symbols in the time domain and modulated by a discrete Fourier transform. Next, the correlation matrices and correlation vectors are estimated from the impulse responses and the spreading codes of all users. Finally, the weight vectors that are obtained from the correlation matrices and correlation vectors are multiplied by the received signal to suppress the multiuser interference. The results of computer simulations indicated that the bit-error-ratio performance obtained using this method was better than that obtained when using the conventional fading compensation scheme or when using conventional MMSEC with the recursive least squares algorithm.

Microcellular radio direct-sequence code division multiple access (DC-CDMA) system using optical link to connect their base stations to a central station is a solution of cost-effective and efficient spectrum reuse to meet the growing demand for mobile communications. In addition to the inherent multiuser interference (MUI) of CDMA signals, the system capacity is significantly reduced by a nonlinear distortion (NLD) due to the nonlinearity of optical link. In this paper, a two-stage cancellation technique is introduced into the system to cancel both the MUI and the NLD. It is performed at the receiver of the central station where the random ingredients of all user signals are estimated, and the MUI and the NLD are rebuilt and removed from the received signal. The validity of the cancellation technique is theoretically analyzed and shown by the numerical results. The analytical method and its results are also applicable to other general nonlinear CDMA.

This paper evaluates the performance of DS/CDMA with diversity coding and multiuser interference (MUI) cancellation in fading multipath channel. The diversity technique considered in this paper, is different from the conventional scheme and transmits different information over different channels. It is shown that, this diversity scheme performs better than conventional diversity scheme, and when combined with MUI cancellation provides significant performance improvement. Effects of partial band jamming on the system are also considered.