Continuous Analog Channel Estimation Aided Beamforming for Massive MIMO Systems
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Analog beamforming is an attractive solution to reduce the implementation cost of massive antenna transceivers by using few up/down-conversion chains. However, reduction in the number of up/down-conversion chains leads to an increase in channel estimation (CE) overhead when conventional digital CE techniques are used. This paper introduces a novel CE technique called continuous analog channel estimation (CACE), that can be performed without digital processing, enables analog beamforming at the receiver and additionally provides resilience against oscillator phase-noise. In CACE a reference tone is transmitted continuously with the data signals, and the receiver uses the received signal for reference as a matched filter for combining the data signals, albeit via analog processing. By avoiding digital processing, the CE overhead with CACE is reduced significantly and furthermore becomes independent of the number of antenna elements. We propose a receiver architecture for CACE, analyze its performance in the presence of oscillator phase-noise, and derive near-optimal system parameters. Transmit beamforming and initial access procedure with CACE are also discussed. Simulations confirm that, in comparison to conventional CE, CACE suffers only a small loss in signal-to-interference-plus-noise-ratio, while providing phase-noise resilience and a significant reduction in the CE overhead.
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