An iterative semi-blind multiuser detector for coded MC-CDMA uplink

Abstract

Iterative multiuser detection is a powerful signal processing technique to increase performance and capacity of coded CDMA systems. However, previously proposed iterative multiuser receivers have been based on complete knowledge of spreading codes of all users in the system. Performance of these receivers degrades significantly in the presence of unknown interference, caused by out-of-cell users whose spreading codes are not known. A significant part of the interference in a typical uplink system is often due to such unknown users. In this paper, we propose an iterative semi-blind receiver for a coded system in such an uplink environment. It is based on the minimum mean square error criterion. The proposed iterative receiver utilizes known users' information for the computation of log-likelihood ratios, while blindly suppressing unknown interference. We consider a multicarrier CDMA system, which has received considerable attention for future high-speed wireless systems. Turbo code is used for channel coding, with log-MAP decoding. Simulation results demonstrate that the proposed iterative semi-blind method offers substantial performance gain over that of the conventional noniterative and non blind iterative receivers.