Advanced Multiuser Detection Methods for DS-CDMA Systems

The aim of this project is tho identify advanced efficient multiuser detection/decoding methods for DS-CDMA (Direct Sequence-Code Division Multiple Access) format in mobile radio communications. Conventional sub-optimal multiuser detectors are derived under the assumption that the channel is known. However, these schemes are sensitive to estimation errors of the channel parameters. A promising solution is JDE (Joint data Detection and channel Estimation). Two sub-optimal iterative JDE receiver architectures have been developed. One is based on the EM (Expectation-Maximization) algorithm and the other results from an application of the SAGE (Space Alternating Generalized EM) algorithm. Recently, the appealing features of EM-based JDE like i) robustness against channel estimation errors ii) near-far resistance, iii) large multiuser efficiency, iv) fast convergence rate have attracted industry. In collaboration with RTX Telecom A/S, Denmark, the SAGE-JDE scheme is currently extended to time-variant frequency-selective fading [Kocian and Fleury-03b]. The resulting receiver architecture are optimized and implemented in a mobile terminal operating in a Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) system, a candidate for the third generation mobile communication system in China. (Alexander Kocian and Bernard H. Fleury)