Semi-Data-Aided Channel Estimation for MIMO Systems via Reinforcement Learning

Data-aided channel estimation is a promising solution to improve channel estimation accuracy by exploiting data symbols as pilot signals for updating an initial channel estimate. In this paper, we propose a semi-data-aided channel estimator for multiple-input multiple-output communication systems. Our strategy is to leverage reinforcement learning (RL) for selecting reliable detected symbols, then update the channel estimate by utilizing only the selected symbols as additional pilot signals. Towards this end, we first define a Markov decision process (MDP) which sequentially decides whether to use each detected symbol as an additional pilot signal. We then develop an RL algorithm to find an effective policy of the MDP based on a Monte Carlo tree search approach. In this algorithm, we exploit the a-posteriori probability for approximating both the optimal future actions and the corresponding state transitions of the MDP and derive a closed-form expression for the optimal policy under the approximations. A key advantage of the proposed channel estimator is that it requires less computational complexity than conventional iterative data-aided channel estimators. Simulation results demonstrate that the proposed channel estimator effectively mitigates both channel estimation error and detection performance loss caused by insufficient pilot signals.

I. Introduction

Multiple-input multiple-output (MIMO) communication is one of the core technologies in modern wireless standards. The use of multiple antennas significantly improves both the capacity and the reliability of wireless systems by providing spatial multiplexing and diversity gains [2], [3], [4]. A key requirement to enjoy these benefits is accurate channel state information (CSI) at both transmitter and receiver. For example, the capacity of MIMO communication systems increases linearly with the number of either transmit or receive antennas under the premise that perfect CSI is available at both the transmitter and receiver [2], [3].