  Massive multiple-input multiple-output (MIMO) is expected to play a central
role in future wireless systems. The deployment of large antenna arrays at the
base station and the mobile users offers multiplexing and beamforming gains
that boost system spectral efficiency. Unfortunately, the high cost and power
consumption of components like analog-to-digital converters makes assigning an
RF chain per antenna and applying typical fully digital precoding/combining
solutions difficult. In this paper, a novel architecture for massive MIMO
receivers, consisting of arrays of switches and constant (non-tunable) phase
shifters, is proposed. This architecture applies a quasi-coherent combining in
the RF domain to reduce the number of required RF chains. An algorithm that
designs the RF combining for this architecture is developed and analyzed.
Results show that the proposed massive MIMO combining model can achieve a
comparable performance to the fully-digital receiver architecture in
single-user and multi-user massive MIMO setups.
