Bit-error-rate minimisation in multiuser transmission schemes for multiple-input–multiple-output communication with increasing number of base station antennas

Multiuser transmission (MuT) can be carried out at the base station of a multiple-input-multiple-output system for mitigating the downlink multiuser interference, achieving a near-single-user performance at the mobile terminals. These MuT systems can be designed for optimising different performance metrics, such as the bit-error-rate (BER), which is the focus of this study. In order to mitigate the MuT´s complexity, a convex formulation for the minimum BER (MinBER) optimisation problem is proposed, by employing some slight modifications on its original formulation. The authors have shown that the novel convex formulation makes the application of some optimisation algorithms very efficient, leading to a reduced complexity and enabling the system operation in higher dimensions. Indeed, the authors also show that in these conditions the MinBER-MuT system presents the most noticeable gains in performance. The results demonstrate that, among the investigated techniques, the proposed Line Search Quasi-Newton algorithm relying on the penalty function approach results in the best performance versus complexity trade-off in the context of high capacity multiuser systems.