Beamforming for Reduced-Rank MIMO Interference Channels in Dynamic TDD Systems

Dynamic Time Division Duplexing (DynTDD) enables flexible time slot allocation based on changing communication needs, which distinguishes it from traditional Time Division Duplexing (TDD) systems that rely on fixed time slot allocation. However, despite the benefits offered by DynTDD, cross-link interference (CLI) can still occur when neighboring cells use different transmission directions on the same or partially-overlapping time-frequency resources. Two types of cross-link interference exist: Base Station (BS) to BS or Downlink (DL) to Uplink (UL) interference, and User Equipment (UE) to UE or UL to DL interference. To address this interference, coordinated beamforming is a crucial signal-processing technique. This study focuses on designing zero-forcing (ZF) transmit beamforming at initialization, and the iterative weighted minimum mean-square error (WMMSE) algorithm to maximize the sum rate in a Multiple Input Multiple Output (MIMO) User Equipment to User Equipment (UE-to-UE) Interference Channel (IC). The study also examines the potential advantages of non-uniform Degrees-of-Freedom (DoF) at Uplink (UL) and/or Downlink (DL) User Equipment (UEs), which can enhance the sum DoF, leading to higher sum rates at high Signal-to-Noise Ratio (SNR).