Achieving Massive MIMO Gains in the FDD System for 5G: An Environment-Aware Perspective

The performance of a frequency division duplexing (FDD) massive multiple input multiple output (MIMO) system is traditionally limited by the large amount of overhead for downlink channel training and uplink channel state information (CSI) feedback. In this paper, we propose an environment-aware scheme to exploit massive MIMO gains in the FDD mode. Under a quasi-static scattering geometry and slow user mobility, the propagation environment can be known at a low cost. Given a priori environment information, the angular domain channel statistics can be obtained accordingly. In the proposed scheme, the angular domain is partitioned into several angular bins and the same number of predefined precoding vectors are generated accordingly. Based on the environment-specific angular domain information, the system topology is modeled as a bipartite graph. An efficient user scheduling algorithm is proposed, which is equivalent to finding a match of the bipartite graph, and a remarkable multiplexing gain is achieved by removing the overlapped angular bins. After user scheduling, each selected user is allocated to one predefined precoding vector. The numerical results have confirmed the validity of the proposed scheme.