Hybrid Equalization for mmWave Cell-Free Radio Stripes-Based Systems

Cell-free (CF) massive multiple-input multiple-output (mMIMO) stands out as a promising technology for 6G networks, offering distributed antennas over a geographical area rather than fixed base stations (BSs). Yet, the conventional CF network, with its star typologies, limits its practical implementation due to the high fronthaul and computational overhead. Consequently, integrating radio stripes (RS) with CF systems appears as a realistic and cost-effective approach to address these challenges, thereby enhancing system efficiency and scalability. In this paper, we propose a novel hybrid analog-digital equalization algorithm, specifically designed for wideband millimeter wave (mmWave) CF mMIMO systems with RS deployment. To design the hybrid equalizer, the proposed algorithm uses only local channel information and some side information forwarded by the preceding AP. The APs analog equalizer is optimized based on the overall mean squared error (MSE) between the transmitted and received signals. Simulation results show that this sequential hybrid approach significantly reduces the signaling and information exchange demands.