Performance of Multiway Relay DS-CDMA Systems over Nakagami-m Fading Channels

A multiway relay direct-sequence code-division multiple-access (MR-DS-CDMA) system is proposed for exchanging information among a group of distributed mobile terminals (MTs). In order to implement information exchange, a MT having similar distances from the other MTs is chosen to act as a relay, which assists the whole group of MTs to achieve their information exchange within two time-slots. In our proposed MR-DS-CDMA system, the relay is operated in detection-and-forward (DF) relaying strategy. Signals at the relay and the MTs are detected in the principles of minimum mean-square error multiuser detection (MMSE-MUD) or of the receiver multiuser diversity assisted multi-stage MMSE MUD (RMD/MS-MMSE MUD). The error performance of the MR-DS-CDMA is investigated, when communicating over Nakagami-m fading channels. Our studies show that the MR-DS-CDMA employing the RMD/MS-MMSE MUD at both the relay and MTs constitutes a high-efficiency information exchange system. It has low delay, promising error performance and low-complexity. Furthermore, it is robust to system overloading, where the number of MTs supported is higher than the spreading factor of the DS-CDMA system.