Low Complexity Polynomial Expansion Detector for Massive MIMO Uplink with Multiple-Antenna Users

In this paper, a low complexity polynomial expansion (PE) detector for massive multi-input multi-output (MIMO) uplink transmissions is proposed. In contrast to most massive MIMO systems in the literature, where single-antenna user equipments (UEs) are assumed, multiple-antenna UEs are employed in this paper. Furthermore, each link between a user and the base station forms a jointly correlated Rician fading channel. The PE detector reduces the complexity of the minimum mean square error (MMSE) detector by replacing the matrix inversion with an approximate matrix polynomial. In the design of the low complexity PE detector, the approximations of the moments of the channel Gram matrix are needed. We use operator- valued free probability to derive these approximations. The low complexity PE detector is easy to compute. Simulation results show that it can achieve performance close to the MMSE detector.