  Analog beamforming is an attractive and cost-effective solution to exploit
the benefits of massive multiple-input-multiple-output systems, by requiring
only one up/down-conversion chain. However, the presence of only one chain
imposes a significant overhead in estimating the channel state information
required for beamforming, when conventional digital channel estimation (CE)
approaches are used. As an alternative, this paper proposes a novel CE
technique, called periodic analog CE (PACE), that can be performed by analog
hardware. By avoiding digital processing, the estimation overhead is
significantly lowered and does not scale with number of antennas. PACE involves
periodic transmission of a sinusoidal reference signal by the transmitter,
estimation of its amplitude and phase at each receive antenna via analog
hardware, and using these estimates for beamforming. To enable such non-trivial
operation, two reference tone recovery techniques and a novel receiver
architecture for PACE are proposed and analyzed, both theoretically and via
simulations. Results suggest that in sparse, wide-band channels and above a
certain signal-to-noise ratio, PACE aided beamforming suffers only a small loss
in beamforming gain and enjoys a much lower CE overhead, in comparison to
conventional approaches. Benefits of using PACE aided beamforming during the
initial access phase are also discussed.
