Iterative Channel Estimation, Detection and Decoding for Multi-Antenna Systems with RIS

This work proposes an iterative channel estimation, detection and decoding (ICEDD) scheme for the uplink of multi-user multi-antenna systems assisted by multiple reconfigurable intelligent surfaces (RIS)}. A novel iterative code-aided channel estimation (ICCE) technique is developed that uses low-density parity-check (LDPC) codes and iterative processing to enhance estimation accuracy while reducing pilot overhead. The core idea is to exploit encoded pilots (EP), enabling the use of both pilot and parity bits to iteratively refine channel estimates. To further improve performance, an iterative channel tracking (ICT) method is proposed that takes advantage of the temporal correlation of the channel. An analytical evaluation of the proposed estimator is provided in terms of normalized mean-squared error (NMSE), along with a study of its computational complexity and the impact of the code rate. Numerical results validate the performance of the proposed scheme in a sub-6 GHz multi-RIS scenario with non-sparse propagation, under both LOS and NLOS conditions, and different RIS architectures.