Iterative space-time processing for multiuser detection in multipath CDMA channels

Huaiyu Dai*, Student Member, IEEE, and H. Vincent Poor, Fellow, IEEE Department of Electrical Engineering, Princeton University Princeton, NJ 08540 Tel: (609) 258-4634 Fax: (609) 258-1560 Email: [email protected], [email protected] Abstract: Space-time processing and multiuser detection are two promising techniques for combating multipath distortion and multiple-access interference in CDMA systems. To overcome the computational burden that rises very quickly with increasing numbers of users and receive antennas in applying such techniques, iterative implementations of several space-time multiuser detection algorithms are considered here. These algorithms include iterative linear space-time multiuser detection, Cholesky iterative decorrelating decision-feedback space-time multiuser detection, multistage interference cancelling space-time multiuser detection, and EM-based iterative space-time multiuser detection. A new space-time multiuser receiver structure that allows for efficient implementation of iterative processing is also introduced. Fully exploiting various types of diversity through joint space-time processing and multiuser detection brings substantial gain over single-receiver-antenna or single-user based methods. It is shown that iterative implementation of linear and nonlinear space-time multiuser detection schemes discussed in this paper realizes this substantial gain and approaches the optimum performance with reasonable complexity. Among the iterative space-time multiuser receivers considered in this paper, the EM-based (SAGE) iterative space-time multiuser receiver introduced here achieves the best performance with excellent convergence properties. Index Terms Antenna arrays, CDMA, iterative processing, multiuser detection, SAGE, space-time processing