Wideband Full-Duplex Phased Array With Joint Transmit and Receive Beamforming: Optimization and Rate Gains

Full-duplex (FD) wireless and phased arrays are both promising techniques that can significantly improve data rates in future wireless networks. However, integrating FD with transmit (Tx) and receive (Rx) phased arrays is extremely challenging, due to the large number of self-interference (SI) channels. Previous work relies on either RF canceller hardware or on analog/digital Tx beamforming (TxBF) to achieve SI cancellation (SIC). However, Rx beamforming (RxBF) and the data rate gain introduced by FD nodes employing beamforming have not been considered yet. We study FD phased arrays with joint TxBF and RxBF with the objective of achieving improved FD data rates. The key idea is to carefully select the TxBF and RxBF weights to achieve wideband RF SIC in the spatial domain with minimal TxBF and RxBF gain losses. Essentially, TxBF and RxBF are repurposed, thereby not requiring specialized RF canceller circuitry. We formulate the corresponding optimization problem and develop an iterative algorithm to obtain an approximate solution with provable performance guarantees. Using SI channel measurements and datasets, we extensively evaluate the performance of the proposed approach in different use cases under various network settings. The results show that an FD phased array with 9/36/72 elements can cancel the total SI power to below the noise floor with sum TxBF and RxBF gain losses of 10.6/7.2/6.9dB, even at Tx power level of 30dBm. Moreover, the corresponding FD rate gains are at least 1.33/1.66/1.68 ×.

I. Introduction

Full-duplex (FD) wireless – simultaneous transmission and reception on the same frequency – has the potential to double the throughput and reduce latency, thereby has attracted significant attention [2], [3]. The fundamental challenge associated with FD wireless is the vast amount of self-interference (SI) leaking from the transmitter (Tx) into the receiver (Rx), which needs to be canceled to successfully recover the desired signal. Recent work has demonstrated practical levels of SI cancellation (SIC) at the antenna interface, RF/analog, and digital baseband [4]–[8].