Minimum BER Transmit Power Allocation and Beamforming for Two-Input–Multiple-Output Spatial Multiplexing Systems

A two-input-multiple-output (TIMO) system represents an important special case of multiple-input-multiple-output (MIMO) systems in practical scenarios. In this paper, transmit optimization for TIMO spatial multiplexing systems is investigated. Minimum bit-error rate (MBER) is employed as the optimization criterion. Approximate MBER transmit power allocation for a variety of receiver structures is proposed, including zero-forcing, successive interference cancellation (SIC), and ordered SIC. Transmit-beamforming schemes using 4-ary pulse-amplitude modulation and quaternary phase-shift keying premixing are also proposed, which eliminate error floors in ill-conditioned TIMO channels. It is shown both analytically and by numerical simulations that the proposed schemes offer superior performance compared to existing schemes