Multi-Hop Massive MIMO Relay Networks

The asymptotic performance of multi-user multihop massive multiple-input multiple-output (MIMO) relay networks, in which multiple spatially distributed user nodes communicate with a multiple-antenna destination via multi-antenna amplify-and-forward relays, is investigated. To this end, the signal-to-interference-plus-noise ratio and achievable sum rate expressions are derived for three specific antenna configurations at the relay and destination nodes, namely (i) infinitely many relay and destination antennas, (ii) finitely many relay antennas and infinitely many destination antennas, and (iii) finitely many relay and destination antennas. The asymptotic achievable sum rates are derived when the numbers of antennas at the relays and destination grow unbounded while keeping fixed ratios among them. The upper and lower bounds of the average sum rates are derived for the finite antenna regime by using bounds for harmonic mean and Jensen's inequality. The detrimental effects of channel estimation errors are investigated by deriving the achievable sum rate expressions. Our sum rate analysis reveals that the massive MIMO technology can be exploited to achieve significant spectral efficiency gains for multi-hop relay networks.