Minimum variance multiuser detection for dual rate and space-time coded DS-CDMA systems

Minimum Variance multiuser receivers are designed in dual rate DS-CDMA (direct-sequence code-division multiple-access) system, and in space-time coded DS-CDMA systems. Their performances are analyzed. The proposed Minimum Variance receivers are designed to pass desired signals without distortion, meanwhile minimizing the overall interference signals, irrespective of their origins. Additionally, the Minimum Variance receiver requires only the spreading codes and timing for the desired user and can be conveniently implemented using adaptive schemes.; In dual rate CDMA systems, a low rate user has a symbol period which is M times of that of a high rate user. A bank of M receivers can be designed to detect those M symbols for a high rate user by minimizing the total output power of these receivers subject to a common constraint for all M receivers. The unknown constraint can be obtained by further maximizing the resulting power. It is shown that the performance of the proposed receivers tends to be close to that of the minimum mean squared error (MMSE) receiver at high SNR.; In space-time coded DS-CDMA systems, over frequency flat fading channels and over frequency selective fading channels, it is shown both analytically and numerically that the Minimum Variance receiver achieves similar performance in terms of the output SINR (signal-to-interference-and-noise ratio) to that of the linear optimum MMSE receiver over a wide range of the input SNR (signal-to-noise ratio). It is also shown that the ratio of the output SINR of the Minimum Variance receiver to that of the MMSE receiver converges to a constant very close to one at high SNR. The Minimum Variance receiver also yields a blind channel estimate which, converges to the true channel parameters (within a scalar ambiguity) as the SNR increases.