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Pilot design for FDD massive MIMO systems with channel sparsity in delay-angle domain

Channel state information (CSI) is essential for realizing the benefits of massive MIMO systems, but the pilot overhead for acquisition the CSI is tremendous, especially for frequency division duplex (FDD) massive MIMO systems. In order to reduce the pilot overhead, we propose a decoupling pilot design scheme. The proposed pilot design scheme fully utilizes the channel sparsity in delay-angle domain which caused by the small amount of scatterers in the physical propagation environment. By exploiting the joint sparsity, the pilot design is decoupled into two domains. In angle domain, random Rademacher distribution pilot matrix is adopted. In delay domain, a two-layer greedy iterative (TLGI) algorithm is proposed to obtain the near-optimal pilot subcarrier pattern. Simulation results verify that the proposed pilot design scheme achieves the similar performance with half of the pilot overhead compared with the random pilot pattern.