Decoupling Channel Estimation for FDD Massive MIMO Systems Utilizing Joint Sparsity

Effective channel estimation for massive multiple-input-multiple-output (MIMO) systems based on frequency division duplex (FDD) protocol is a crucial problem. To reduce pilot overhead, we consider the joint sparsity of the multi-path channel in delay-angle domain. Based on the joint sparsity, we propose a decoupling pilot design scheme. In the proposed scheme, the pilot design is decoupled into two parts. In the first part, a global optimal selection greedy iterative algorithm (GOS-GIA) is proposed to obtain the near-optimal pilot subcarrier pattern. In the second part, a random Rademacher distribution pilot matrix is used as the angle-domain pilot matrix. Accordingly, a two-stage channel estimation strategy is also provided and analyzed. The first stage of the strategy is concerned with retrieving the positions of non-zero dominant taps in the delay domain. The second stage focuses on estimating the channel coefficients at these taps. Algorithm complexity analysis shows that the GOS-GIA can reduce the computational complexity at least one order of magnitude, and the proposed channel estimation strategy reduces the computational complexity by more than two orders of magnitude. Simulation results verify that the proposed pilot design scheme achieves better performance with lower pilot overhead.