  Analog beamforming greatly reduces the implementation cost of massive antenna
transceivers by using only one up/down-conversion chain. However, it incurs a
large pilot overhead when used with conventional channel estimation (CE)
techniques. This is because these CE techniques involve digital processing,
requiring the up/down-conversion chain to be time-multiplexed across the
antenna dimensions. This paper introduces a novel CE technique, called
continuous analog channel estimation (CACE), that avoids digital processing,
enables analog beamforming at the receiver and additionally provides resilience
against oscillator phase-noise. By avoiding time-multiplexing of
up/down-conversion chains, the CE overhead is reduced significantly and
furthermore becomes independent of the number of antenna elements. In CACE, a
reference tone is transmitted continuously with the data signals, and the
receiver uses the received reference signal as a matched filter for combining
the data signals, albeit via analog processing. We propose a receiver
architecture for CACE, analyze its performance in the presence of oscillator
phase-noise, and derive near-optimal system parameters and power allocation.
Transmit beamforming and initial access procedure with CACE are also discussed.
Simulations confirm that, in comparison to conventional CE, CACE provides
phase-noise resilience and a significant reduction in the CE overhead, while
suffering only a small loss in signal-to-interference-plus-noise-ratio.
