A Close to Capacity Double Iterative Based Precoder Design for MU-MIMO Broadcast Channel with Multi-Stream Support

Many algoritms have been proposed for precoders design in a multiuser MIMO system (MU-MIMO). Nevertheless, the proposed solutions showed to have better results for some SNRs (signal to noise ratio) regions and degrade in some other parts. This paper proposes a new double iterative procedure for sum-rate maximization. The proposed algorithm is based on jointly optimizing the precoders and decoders using two different decoding schemes. The solution here is supporting multi streams per user. The algorithm is based on a WMMSE (weighted minimum mean square error) precoder combined with two iterative receivers namely the MF (matched filter) and MMSE (minimum mean square error) decoders. The resulting precoding matrices from the first algorithm (WMMSE/MF) are used as an initialization for the second one (WMMSE/MMSE). The choice of these decoders and their combination has been done according to their properties. Another crucial point in this proposal is the decision on the switching point between these two algorithms. A dynamic algorithm introducing very low extra complexity is proposed here. To validate our proposed solution we compare it with an existing MMSE and WMMSE based iterative optimization algorithms. The obtained results demonstrate significant gains without introducing supplementary complexity. Comparison with DPC (dirty paper coding) performances shows how close our proposed solution is to the BC (broadcast channel) channel capacity.