Sampling-Level Time-Division Multiplexing for Fully Connected MIMO Transmitters: Principle and Prototype Verification

Abstract

Multiple-input multiple-output (MIMO) systems and multibeam phased arrays are essential for modern wireless communications. Conventional fully connected (FC) beamformers achieve the maximum array gain but rely on cross-connection networks with numerous phase shifters, leading to high power consumption and implementation complexity. Recent time-domain techniques have been explored to reduce hardware complexity. However, their application at the transmitter faces challenges related to spectral compliance and hardware nonlinearities. This article presents a sampling-level time-division FC (TDFC) architecture for MIMO transmitters that eliminates physical cross-connection networks. By integrating high-speed switching, synchronized phase shifting, and reconstruction filtering, the architecture emulates FC beam–antenna mapping while preserving spectral control and compatibility with existing digital predistortion (DPD) techniques. Unlike slow time-division multiplexing among beams or users, the proposed architecture preserves concurrent transmission of multiple spatial data streams, thereby enabling spatial multiplexing gains and increased system throughput. An analytical model is developed to guide implementation analysis, and an over-the-air (OTA) prototype verification platform is built to experimentally validate the architectural feasibility and key nonideal effects. Measurement results confirm the analytical findings, demonstrating the spatial multiplexing capability of the TDFC operation and the feasibility of applying DPD in practical implementations.