Iterative semi-blind multiuser detection using subspace approach for MC-CDMA uplink

Iterative multiuser detection is a powerful signal processing technique to enhance the 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. The performance of these receivers degrades significantly in the presence of unknown interference, caused by out-of-cell users whose spreading codes are not known. We propose two forms of iterative semi-blind multiuser receivers for such an uplink environment. The first is based on minimum mean square error criterion and the second is a hybrid scheme, based on a combination of parallel interference cancellation and linear multiuser detection. These receivers are derived using a subspace approach, which utilize known users´ information for the computation of log-likelihood ratios, while blindly suppressing the unknown interference. We consider a multicarrier CDMA system, which has received considerable attention for future high-speed wireless systems. Simulation results demonstrate that the proposed iterative semi-blind methods offer substantial performance gain over that of conventional noniterative and non-blind iterative receivers.