Space-time adaptive detection in turbo-coded DS-CDMA wireless systems over Rayleigh fast-fading channels

This paper investigates the performance improvement due to channel coding in a direct-sequence code-division multiple-access (DS-CDMA) system that employs space-time adaptive minimum mean-square-error (MMSE) interference suppression. A synchronous DS-CDMA transmission is assumed, and we focus on the performance gain attained through error control coding when used with Binary-Phase-Shift-Keyed (BPSK) modulation. It is shown that the use of adaptive antenna array at the receiver side, assists in attenuating multiuser interference and at the same time speeds-up the convergence rate of the adaptive receiver. Both the least-mean-square (LMS) and the recursive-least-square (RLS) adaptive receiver algorithms are considered. Also, a performance comparison between turbo codes and soft-decision convolutional codes (SD-CC) in the space-time system is provided. It is found that the use of antenna arrays at the receiver side helps to bring the adaptive receiver's performance close to its multiuser counterpart. Both analyses and simulations show that the turbo coded system outperforms the convolutionally coded one with a coding gain of approximately 1.7 dB.