Performance of Closed Form and Iterative MU-MIMO precoders for different broadcast channel configurations

We investigate in this paper the performance achieved by some SDMA (Space Division Multiple Access) access techniques in a Broadcast channel configuration. The study includes the two basic linear precoding schemes present in the literature namely the CF (Closed Form) and the Iterative precoding techniques. These techniques have already been widely studied for the i.i.d Rayleigh channel. In fact, these precoding methods are essentially based on the exploitation of diversity created by multipaths present in such a channel to enhance the beamforming design and consequently increase the SINR (Signal to Interference and Noise Ratio) for each user. In this work the impact of a reduction of these degrees of freedom has been investigated through simulations under other channel configurations. The obtained results demonstrate that these precoding techniques remain efficient only for systems offering high number of degrees of freedom and fail when a direct LOS (Line Of Sight) is present limiting the achievable Sum Rate (SR) of the system. The obtained results have also been compared to the TDMA (Time Division Multiple Access) communication mode.