Hybrid CSI-Based Hierarchical Beamforming for Flexible Duplex MIMO Systems

Flexible duplex (FD) techniques, including dynamic time-division duplex and dynamic frequency division duplex, are widely recognized as pivotal solutions to meeting the asymmetric and dynamic traffic demands in cellular systems. However, the coexistence of opposite transmission directions at the same time between neighboring cells inevitably results in cross-link interference (CLI), leading to significant degradation in network throughput. To tackle this issue, we exploit the trade-off between interference cancellation and spatial multiplexing capabilities in FD systems, and develop a hybrid channel state information (CSI) based hierarchical beamforming algorithm to mitigate the CLI. Compared with the existing state-of-the-art schemes, the proposed algorithm can substantially suppress the CLI with a much lower overhead of CSI acquisition between base stations. Simulation results demonstrate the superior performance of our proposed algorithm.