  Massive multiple-input multiple-output (MIMO) relaying is a promising
technological paradigm which can offer high spectral efficiency and
substantially improved coverage. Yet, these configurations face some formidable
challenges in terms of digital signal processing (DSP) power consumption and
circuitry complexity, since the number of radio frequency (RF) chains may scale
with the number of antennas at the relay station. In this paper, we advocate
that performing a portion of the power-intensive DSP in the analog domain,
using simple phase shifters and with a reduced number of RF paths, can address
these challenges. In particular, we consider a multipair amplify-and-forward
(AF) relay system with maximum ratio combining/transmission (MRC/MRT) and we
determine the asymptotic spectral efficiency for this hybrid analog/digital
architecture. After that, we extend our analytical results to account for
heavily quantized analog phase shifters and show that the performance loss with
2 quantization bits is only 10%.
