Performance of Hybrid Beamforming with Hardware Impairments for mmW Massive MIMO Communication in an Urban Scenario

The use of massive MIMO for communication at millimeter-Wave (mmW) frequency bands has become a key enabler to meet the data rate demands of the upcoming fifth generation (5G) cellular systems. In particular, hybrid beamforming solutions are receiving increasing attention as simpler and less expensive alternatives to fully digital precoding schemes. Despite their proven good performance in simple setups, their suitability for realistic cellular systems with many interfering base stations and users is still unclear. Furthermore, the performance of massive MIMO beamforming and precoding methods are in practice also affected by hardware constraints and by the presence of non-ideal devices. In this sense, this paper assesses the performance of digital precoding and hybrid beamforming in an urban cellular system with an accurate mmW channel model under both ideal and realistic assumptions. The results show that hybrid beamforming can reach the performance of fully digital maximum ratio transmission under line of sight conditions and with a sufficient number of parallel radio-frequency (RF) chains, especially when the realistic effects of outdated channel information and per antenna power constraints are considered. This work also shows the impact of real phase shifters and combiners over hybrid beamforming, where the former ones have minor impact on the performance but the latter ones determine the optimum number of RF chains to be used in practice.