Device-Centric ISAC for Exposure Control via Opportunistic Virtual Aperture Sensing

TL;DR

This paper presents a device-centric ISAC approach that uses opportunistic virtual aperture sensing and advanced filtering to accurately measure device-to-body distance, enabling better exposure control and improved communication performance.

Contribution

It introduces a novel method combining virtual aperture sensing with Kalman filtering to localize devices accurately using opportunistic motion data and phase observations.

Findings

Achieves centimeter-level localization accuracy at 28GHz.

Utilizes inertial sensors and phase observations for improved trajectory estimation.

Demonstrates potential for enhanced exposure control in wireless devices.

Abstract

Regulatory limits on Maximum Permissible Exposure (MPE) require handheld devices to reduce transmit power when operated near the user's body. Current proximity sensors provide only binary detection, triggering conservative power back-off that degrades link quality. If the device could measure its distance from the body, transmit power could be adjusted proportionally, improving throughput while maintaining compliance. This paper develops a device-centric integrated sensing and communication (ISAC) method for the device to measure this distance. The uplink communication waveform is exploited for sensing, and the natural motion of the user's hand creates a virtual aperture that provides the angular resolution necessary for localization. Virtual aperture processing requires precise knowledge of the device trajectory, which in this scenario is opportunistic and unknown. One can exploit onboard inertial sensors to estimate the device trajectory; however, the inertial sensors accuracy is not sufficient. To address this, we develop an autofocus algorithm based on extended Kalman filtering that jointly tracks the trajectory and compensates residual errors using phase observations from strong scatterers. The Bayesian Cram\'er-Rao bound for localization is derived under correlated inertial errors. Numerical results at 28GHz demonstrate centimeter-level accuracy with realistic sensor parameters.