Adaptive Modulus RF Beamforming for Enhanced Self-Interference Suppression in Full-Duplex Massive MIMO Systems

TL;DR

The paper addresses the challenge of strong self-interference in full-duplex massive MIMO by leveraging a uniform rectangular array with sub-connected hybrid beamforming and a non-constant modulus RF beamforming scheme. It jointly optimizes perturbed uplink/downlink beam directions and Tx/Rx gain controllers using a swarm-intelligence (PSO) approach, constrained by directivity degradation and gain bounds, based on measured SI channels from an anechoic-chamber setup. The proposed NCM-BF-SIS method achieves SI suppression up to $-80~\mathrm{dB}$, with URA configurations offering about $9~\mathrm{dB}$ more suppression than ULA sub-arrays, and demonstrates substantial robustness across a range of beam directions. This work provides a practical, scalable pathway to realize high-performance FD mMIMO with reduced hardware complexity by exploiting spatial DoF via URA SC-HBF and data-driven SI measurements.

Abstract

This study employs a uniform rectangular array (URA) sub-connected hybrid beamforming (SC-HBF) architecture to provide a novel self-interference (SI) suppression scheme in a full-duplex (FD) massive multiple-input multiple-output (mMIMO) system. Our primary objective is to mitigate the strong SI through the design of RF beamforming stages for uplink and downlink transmissions that utilize the spatial degrees of freedom provided due to the use of large array structures. We propose a non-constant modulus RF beamforming (NCM-BF-SIS) scheme that incorporates the gain controllers for both transmit (Tx) and receive (Rx) RF beamforming stages and optimizes the uplink and downlink beam directions jointly with gain controller coefficients. To solve this challenging non-convex optimization problem, we propose a swarm intelligence-based algorithmic solution that finds the optimal beam perturbations while also adjusting the Tx/Rx gain controllers to alleviate SI subject to the directivity degradation constraints for the beams. The data-driven analysis based on the measured SI channel in an anechoic chamber shows that the proposed NCM-BF-SIS scheme can suppress SI by around 80 dB in FD mMIMO systems.

Figures (3)

• Figure 1: System model of FD mMIMO HBF communications system.
• Figure 2: Achieved SI suppression of proposed NCM-BF-SIS with 2$\times$2 sub-array at 20 MHz bandwidth. (a) versus $\psi_D$ and $\psi_U$ for fixed ($\theta_D = \theta_U = 90^\circ$). (b) versus $\theta_D$ and $\theta_U$ for fixed ($\psi_D = \psi_U = 90^\circ$). (c) versus $\psi_D$ and $\theta_D$ for fixed ($\theta_U = \psi_U = 90^\circ$).
• Figure 3: Achieved SI suppression of proposed NCM-BF-SIS with 4$\times$4 sub-array at 20 MHz bandwidth. (a) versus $\psi_D$ and $\psi_U$ for fixed ($\theta_D = \theta_U = 90^\circ$). (b) versus $\theta_D$ and $\theta_U$ for fixed ($\psi_D = \psi_U = 90^\circ$). (c) versus $\psi_D$ and $\theta_D$ for fixed ($\theta_U = \psi_U = 90^\circ$).