Performance of feedback multiple-input-multiple-output system aided by polarisation multiplexing and pre-processing

In this study, the authors investigate the performance of a multi-user downlink (DL) multiple-input-multiple-output (MIMO) system aided by polarisation multiplexing (PM) and multi-user transmitter pre-processing (MUTP). Dual- and triply-polarised antennas that are called on to establish PM offer the advantage of replacing uni-polarised antennas that impose space constraints. In a multi-user scenario, users conflict multi-user interference (MUI). In this contribution, the DL-MUI is suppressed with the aid of pre-processing operated at the base station. To be specific, two pre-processing approaches are considered in their study which are based on singular value decomposition. Both the approaches exploit the channel impulse responses (CIRs) of all the users to formulate the pre-processing matrix and that the second approach which is a joint multi-user transmission and detection technique exploits only user specific CIRs to formulate the post-processing matrix. In their contribution, the required CIRs for formulating the pre-processing matrix are acquired via noisy feedback channels that endure fading as well as delay. Simulation results demonstrate that noise and fading tainted CIRs based MUTP results in performance degradation in terms of the attainable symbol-error-rate (SER) and sum-capacity. Moreover, it is inferred that further degradation results when the feedback channels experience delay. However, their study shows that the application of dual or triply-polarised antennas in conjunction with MUTP can serve as an efficient approach for the DL of the feedback MIMO system, as the achievable sum-capacity and SER under ideal feedback remain close to that attained with the perfect CIRs hypothesis. Furthermore, it is observed that the considered MUTP techniques result in superior SER performance compared with their multi-user detection counterpart and other widely known pre-processing techniques.