Pilot Scheduling on Demand: Adaptive Channel Estimation Scheme for TDD Massive MIMO With Diverse Coherence Times

Abstract

In time-division duplex (TDD) massive multiple-input multiple-output (MIMO) systems, users send pilot sequences for channel state estimation in a fixed time interval, which leads to pilot redundancy if users undergo longer coherence time than the prescribed channel estimation interval, and consequently reduces the net sum spectral efficiency of the systems. In this paper, we propose an adaptive channel estimation scheme for TDD massive MIMO systems, where base stations can reuse the aged channel state information (CSI) by exploiting the temporal correlation inherent in channel aging. We introduce a Fisher transformation method for temporal correlation estimation to determine the CSI estimation interval. We also derive the closed-form expressions of the spectral efficiency with channel aging effect and design a threshold to control the channel aging error introduced by CSI reuse. Numerical results demonstrate that our proposed adaptive scheme yields significant performance gains in spectral efficiency across various communication scenarios.