Beam Design with Quantized Phase Shifters for Millimeter Wave Massive MIMO

In this paper, beam design for millimeter wave (mmWave) massive MIMO systems is studied regarding quantized phase shifters and different number of RF chains. Given the objective beam, the beam design problem is formulated as a hybrid optimization problem involving continuous variables as well as discrete variables. To reduce the difficulty in solving this problem, it is converted into several discrete optimization subproblems. Then beam design methods are proposed for the system with only one RF chain and two RF chains, respectively. For the general system with more than two RF chains, the parameter estimation is incorporated into the random search. Based on these findings, a partial random search (PRS) based beam design algorithm is proposed. To further improve the convergence speed, a fast search (FS) based beam design algorithm is proposed. Simulation results verify the effectiveness of the proposed algorithms and show that the beam pattern using the proposed PRS and FS based algorithm can well approach the objective beam with much less RF chains than OMP.