Joint Transmit and Receive Wideband Beamforming for Spatial SIC in STAR Phased Array Systems

In simultaneous transmit and receive (STAR) phased array systems that suffer from the strong coupling self-interference (SI), the air interface of the receive array is severely saturated. Aiming at this issue, we propose a near-field joint transmit beamforming (TxBF) and receive beamforming (RxBF) spatial SIC scheme. Maintaining the air-interface unsaturation at the receive elements, the proposed scheme aims at minimizing the loss of effective isotropic radiated power (EIRP) and maximizing the signal to interference plus noise ratio (SINR) to obtain the amplitude and phase adjustment coefficients for TxBF and RxBF. The TxBF is optimized by minimizing the EIRP loss. Then, the numerical optimal solution based on the semi-definite relaxation (SDR) method and the analytical suboptimal solution based on the improved subspace method are obtained. On the other hand, the corresponding RxBF is optimized by maximizing the SINR, and the analytical optimal solution is obtained based on generalized Rayleigh quotient properties. Based on the proposed optimal TxBF and RxBF scheme, the relationship between the EIRP loss and the saturation power constraint for the low noise amplifier (LNA) is theoretically analyzed, and the upper bound of SINR performance is derived. To verify the feasibility of the proposed joint TxBF and RxBF spatial SIC scheme, we develop a hardware prototype testbed consisting of 1 transmit panel and 1 receive panel with 64 antenna elements per panel. Results show that the proposed TxBF scheme only causes an EIRP loss of 0.21 dB in the simulation and 1.07 dB in the testbed while maintaining the unsaturation for all receive elements, and the SINR performance of the joint beamforming scheme is 70 dB higher than that of the non-adaptive beamforming.