Transceiver design in dynamic TDD with reduced-rank MIMO interference channels

In Dynamic Time Division Duplexing (DynTDD), the time slot allocation can be changed dynamically based on the changing communication requirements. This provides greater flexibility compared to traditional Time Division Duplexing (TDD) systems, where the time slot allocation is fixed. However, the advantages of the DynTDD system are difficult to fully utilize due to the cross-link interference (CLI) arising from neighboring cells using different transmission directions on the same or partially- overlapping time-frequency resources. There are two types of cross-link interference; between the Base Stations (BS), which is known as BS-to-BS or DL-to-UL interference, and between User Equipment (UE) which is known as UE-to-UE or UL-toDL interference. Coordinated beamforming is an important signal-processing technique for interference mitigation in a cellular communication system. This paper studies zero-forcing (ZF) transmit beamforming design at initialization with and without water-filling, and the iterative weighted minimum mean-square error (WMMSE) algorithm to maximize the sum rate in Multiple Input Multiple Output UE-to-UE Interference Channel (MIMO-IC). This paper also investigates the nonuniform Degrees-of-Freedom (DoF) at UL UEs and/or at DL UEs which could increase the sum of DoF that is represented by the slope of the sum rate and leads to a higher sum rate at high SNR.