On the performance of MBER based receive beamforming for heterogeneous interference mixture

The Minimum Bit Error Rate (MBER) Criterion based system optimisation has been found to outperform the traditional Linear Minimum Mean Square Error (L-MMSE) methods in various design problems like transmit precoding, channel equalization, channel estimation, multi-user detection in CDMA channels, and other conventional problems where MSE was predominantly used as the design criteria. The best possible linear beamformer that can be obtained has been shown to be the one given by the Linear-MBER method in [1], where, however, only a homogeneous interference model, with the desired user and the interferers having same modulation alpahabet, is considered. In this paper, we study the performance of the MBER based receive beamformer for a more realistic case when the interference seen by the desired user is a heterogeneous mixture, with each interferer coming from a different and possibly higher order modulation alphabet. In particular, we show that the analytical bit error rate evaluated for the Linear-MBER method takes a significant performance hit when the interference is from a heterogeneous mixture.