Hybrid Precoding with Two-layer Phase Shifter Feeding Network for MmWave FD-MIMO Systems

Hybrid analog/digital precoding provides an effective solution for millimeter wave (mmWave) multi-input multi-output (MIMO) systems since it reduces the number of radio frequency (RF) chains significantly. Meanwhile, full-dimension MIMO (FD-MIMO) has attracted considerable interests due to its spatial separation ability in vertical direction. However, the hardware complexity of phase shifter (PS) feeding network in the conventional full-connection architecture is too large. In this paper, we propose a novel two-layer PS feeding network architecture for mmWave FD-MIMO systems. Specifically, the two-layer PS network consists of a vertical PS layer and a horizontal PS layer, which greatly reduces the number of PSs required. Furthermore, an iterative precoding design algorithm is proposed, in which the vertical and horizontal beamformers are alternately configured in an iterative fashion. Asymptotic analysis proves that our proposed scheme could exactly approach the performance of full-connection architecture when vertical channel angle spread tends to zero. Simulation results demonstrate that the proposed scheme achieves satisfactory performance while only imposing relatively low hardware complexity compared with its conventional counterparts.