Power scaling laws for massive MIMO relay systems with linear transceivers

In this paper, we study the uplink of a relay-assisted multiuser massive MIMO system. The relay station (RS) equipped with M₁ antennas processes the received signal from K single-antenna users, using maximum ratio combining (MRC)/zero-forcing (ZF) detection, and then forwards the post-processed signal to the base station (BS) with M₂ antennas, according to the all-pass relay protocol. In particular, we derive closed-form approximations of the ergodic achievable rate lower bounds, assuming that MRC/ZF combining is performed at the BS. Furthermore, we examine the power scaling law of the proposed system, and find that the transmit powers of relay or users can be reduced in proportion to M₁ or M₂, respectively, without any loss in the achievable rate.