Multiuser Massive MIMO AF Relaying: Spectral Efficiency and Power Allocation

In this paper, we investigate the uplink and downlink transmission of a relay-aided multiuser massive multiple-input multiple-output amplify-and-forward relaying system. In the uplink, the relay station (RS) processes the received signal from K single-antenna mobile users, using maximum ratio combining or zero forcing (ZF), and then forwards the post-processed signal to the base station (BS) which employs the same processing to recover the user signals. In the downlink, the BS processes the signal using maximum ratio transmission or ZF precoding, forwards the post-processed signal to the RS, and then the RS processes the received signals using the same processing used at the BS and then forwards to the K users. In particular, we derive the ergodic spectral efficiency lower bound in closed-form for both uplink and downlink. Furthermore, we examine the power scaling laws and find that the transmit power of nodes can be cut down by a factor of the number of antennas without any performance loss. Finally, we solve the power allocation problem for sum spectral efficiency maximization and presented the power allocation strategy for the considered processing schemes.