DoA Estimation of Nonuniform Noise Sources via Off-Grid SBL in a Noncooperative Mode Using a Single RF Link

Abstract

With the advancement of integrated sensing and communication (ISAC) technologies, integrating sensing capabilities to commercial-off-the-shelf (COTS) communication devices has been at the forefront of research. Typically, these systems utilize antenna arrays configured across multiple radio frequency (RF) links to capture channel parameters such as direction of arrival (DoA). However, this architecture requires equipping each antenna with an independent RF link, increasing complexity and cost. Additionally, deploying sensing systems necessitates precalibration of the RF links to achieve the desired performance, further laboring deployment. To address these challenges, we design a switched antenna array (SAA) that can time-division activate each antenna within the coherence time on a single RF link, thus simulating a multi-RF links platform for accurate DoA estimation. Subsequently, a switching strategy is developed, and a matching algorithm based on random forest is introduced to tackle the issue that signals from different antennas exported from the single RF link cannot be differentiated due to the noncooperative mode between the SAA and the receiver. Additionally, addressing the impact of carrier frequency offset (CFO) caused by transceiver asynchrony on DoA estimation in the SAA system, we compensate for CFO and model its residuals as nonuniform noise. We introduce an off-grid DoA estimation algorithm based on sparse Bayesian learning (SBL), treating noise as its hyperparameter, and apply the expectation maximization (EM) and inverse iteration algorithms to reconstruct nonuniform noise model, aiming to overcome the impact of nonuniform noise on DoA estimation. We build prototype systems and conduct field trials in real-world environments. The experimental results show that our system achieves 3.7° angle of arrival (AoA) and 3.9° elevation of arrival (EoA) median estimation errors by utilizing only a single RF link without the need to perform a precalibration of the links and any modification of the COTS receiver settings.