A Nearly Optimal Hybrid Precoder Design for Downlink Single-Carrier Wideband Massive MIMO Channels

In this paper, an efficient hybrid precoding architecture is proposed for single-carrier (SC) downlink wideband spatially correlated massive MIMO channels. The design of two-stage beamformers is realized by using a virtual sectorization via second-order channel statistics based user grouping. The novel feature of the proposed architecture is that the effect of both inter-group-interference (due to non-orthogonality of virtual angular sectors) and the inter-symbol-interference (due to SC wideband transmission) are taken into account. While designing the analog beamformer, we examine the dimension reduction problem and proper subspace (beamspace) construction (by exploiting the joint angle-delay sparsity map and power profile of the multi-user channel) based on which a highly efficient spatio-temporal digital precoding is proposed.