J oint Optimization of Digital Beamforming and RF Interference Cancellation for SBFD

Subband non-overlapping full duplex (SBFD) re-cently has been proposed to enhance uplink coverage and reduce latency of conventional time division duplex (TDD) systems by allocating frequency non-overlapping uplink (UL) and downlink (DL) subbands within a TDD band. However, if sufficient interference cancellation (IC) is not provided in the spatial and radio frequency (RF) domain, the self-interference (SI) signal from the DL subband will block the UL receiver. In this paper, we propose a two-stage joint optimization of beamforming and RF IC in SBFD systems, specifically tailored for base station deployment. In the first stage, the RF SI canceller is designed based on the SI channel. Two feasible realizations of the RF SI canceller are provided to reduce the number of taps connecting the Tx and Rx RF chains. In the second stage, the baseband precoding is optimized based on the equivalent residual SI channel and the user channel. Simulation results show that the proposed algorithm can support up to 4 layers of precoding with a maximum rate loss of 20.11% in the DL and up to 5 layers of precoding with a rate loss of less than 10% in the UL.