Downlink MIMO Channel Estimation from Bits: Recoverability and Algorithm
This addresses the problem of efficient channel estimation for massive MIMO systems, which is incremental as it builds on existing feedback and estimation methods.
The paper tackles the challenge of acquiring downlink channel state information in FDD massive MIMO systems from limited feedback by proposing a feedback framework with compression, quantization, and a maximum likelihood estimator, achieving recoverability under a double directional model and validating efficacy through numerical experiments.
In frequency division duplex (FDD) massive MIMO systems, a major challenge lies in acquiring the downlink channel state information}\ (CSI) at the base station (BS) from limited feedback sent by the user equipment (UE). To tackle this fundamental task, our contribution is twofold: First, a simple feedback framework is proposed, where a compression and Gaussian dithering-based quantization strategy is adopted at the UE side, and then a maximum likelihood estimator (MLE) is formulated at the BS side. Recoverability of the MIMO channel under the widely used double directional model is established. Specifically, analyses are presented for two compression schemes -- showing one being more overhead-economical and the other computationally lighter at the UE side. Second, to realize the MLE, an alternating direction method of multipliers (ADMM) algorithm is proposed. The algorithm is carefully designed to integrate a sophisticated harmonic retrieval (HR) solver as subroutine, which turns out to be the key of effectively tackling this hard MLE problem.Extensive numerical experiments are conducted to validate the efficacy of our approach.