Channel Feedback in TDD Massive MIMO Systems With Partial Reciprocity

Abstract

It is widely believed that the channel reciprocity holds in time division duplexing (TDD) massive multiple-input multiple-output (MIMO) systems, so the uplink channel feedback is unnecessary. However, due to the constraint of transmission power and hardware complexity, users may use more receiving antennas than transmitting antennas in practical wireless communication systems. In this practical yet important scenario, only partial channel reciprocity holds, and thus channel feedback is still required in TDD massive MIMO systems. Unfortunately, this important topic has not been investigated in the literature. To fill in this gap, we propose an angle-domain support (ADS) based channel feedback scheme for TDD massive MIMO systems with unequal number of receiving and transmitting antennas. Firstly, by utilizing the angle-domain channel sparsity, we illustrate that a small number of elements in angle-domain channel, which are indexed by ADS, can capture the most power of the channel. Then, we propose the base station (BS) can obtain full downlink channel by decomposing the channel into two parts: the ADS and the low-dimensional angle-domain representation indexed by the ADS. At first, due to the partial channel reciprocity, the ADS is obtained by an angle-domain windows based support detection method at the BS without channel feedback. Then, the low-dimensional angle-domain representation indexed by the ADS is quantized and fed back to the BS. Theoretical analysis and simulation results demonstrate that the proposed scheme can achieve the near-optimal achievable sum-rate performance with low channel feedback overhead.