Adaptive minimum bit error rate beamforming assisted receiver for QPSK wireless communication

This paper considers interference limited communication systems where the desired user and interfering users are symbol-synchronized. A novel adaptive beamforming technique is proposed for quadrature phase shift keying (QPSK) receiver based directly on minimizing the bit error rate. It is demonstrated that the proposed minimum bit error rate (MBER) approach utilizes the system resource (antenna array elements) more intelligently, than the standard minimum mean square error (MMSE) approach. Consequently, an MBER beamforming assisted receiver is capable of providing significant performance gains in terms of a reduced bit error rate over an MMSE beamforming one. A block-data based adaptive implementation of the theoretical MBER beamforming solution is developed based on the classical Parzen window estimate of probability density function. Furthermore, a sample-by-sample adaptive implementation is also considered, and a stochastic gradient algorithm, called the least bit error rate, is derived for the beamforming assisted QPSK receiver.