Federated Tomlinson-Harashima Precoding with Common Reference Transformation for MIMO Systems in Wi-Fi 6

Abstract This paper proposes a Federated Tomlinson-Harashima Precoding (F-THP) framework for multiuser MIMO systems under a Wi-Fi 6 architecture. Unlike traditional centralized THP, which requires full channel state information (CSI) from all access points (APs) and involves transmitting large matrices over the backhaul, this paper proposes a federated model that enables distributed channel knowledge processing at edge devices. Local channel updates are aligned through Gram-Schmidt transformation into a common basis before aggregation, reducing communication overhead by up to 25% compared to centralized THP. Simulation results demonstrate that F-THP achieves comparable bit error rate (BER) performance to centralized THP under Rayleigh fading while offering scalability and privacy advantages. Specifically, F-THP shares only transformed subspace components instead of raw channel matrices, ensuring that up to 25% of sensitive CSI data remains confidential. This makes F-THP particularly suitable for real-time Wi-Fi 6 operation in enterprise and IoT edge environments.