Quasi-Orthogonal Combining for Reducing RF Chains in Massive MIMO Systems

We address the issue of reducing the number of radio frequency (RF) chains in large/massive multiple input multiple output systems while retaining their detection performance. For this, we use a hybrid combining approach and formulate a signal to interference plus noise ratio (SINR) maximization problem. We argue that using an orthogonal basis of the channel matrix to maximize the numerator of the SINR is a worthwhile approach to pursue and use it to propose a quasi-orthogonal combining scheme. Simulation results show that the proposed scheme can provide a detection performance and sum rate close to that of a system utilizing a dedicated RF chain for each receive antenna with less number of RF chains and without increasing the overall computational complexity.