Performance analysis of relay-assisted uplink massive MIMO systems with zero-forcing receiver

As one of the most promising candidate technique for the fifth generation (5G) wireless network, massive multiple-input multiple-output (MIMO) has attracted much research interests. However, due to the high path loss and severe shadowing, the cell-edge users may have very poor performance in uplink massive MIMO systems. To overcome this problem, we investigate relay-assisted uplink massive MIMO systems, where K single-antenna users communicate with an N-antenna base station (BS) through an M-antenna relay and N is very large. We use amplify-and-forward (AF) relaying schemes which simply forward scaled versions of its received signals. Assuming the BS can obtain perfect channel state information (CSI) of all the user-relay links and relay-BS links, zero-forcing (ZF) receiver is adopted at the BS. Based on these assumptions, we derive the closed-form expressions for the ergodic achievable rate and outage probability. Numerical and simulation results validate our analysis and show that the relay-assisted massive MIMO systems achieve better performance than direct transmission massive MIMO systems when the links from the users to the BS are weak.