Iterative Soft Interference Cancellation Aided Minimum Bit Error Rate Uplink Receiver Beamforming

Iterative multiuser receivers constitute an effective solution for transmission over multiple access interference (MAI) infested channels, when invoking a combined multiuser detector and channel decoder. Most reduced-complexity methods in this area use the complex-valued minimum mean squared error (CMMSE) multiuser detector (MUD). Since the desired output of BPSK systems is real-valued, minimizing the mean square error (MSE) between the beamformer´s desired output and the real part of the beamformer output has the potential of significantly improving the attainable bit error rate (BER) performance. We refer to this MMSE design as the real-valued MMSE (RMMSE) receiver. In this paper, we explore a new soft-input soft-output (SISO) interference cancellation multiuser detection algorithm based on the novel minimum BER (MBER) criterion. We demonstrate that the MBER turbo receiver outperforms both the CMMSE and the RMMSE algorithms, particularly in so-called ´overloaded´ beamforming systems, where the number of receiver antennas is lower than the number of users supported