Exposure-Aware Beamforming for mmWave Systems: From EM Theory to Thermal Compliance

TL;DR

This paper introduces a novel exposure-aware beamforming approach for mmWave systems that incorporates electromagnetic and thermal effects, ensuring safety compliance while optimizing communication performance.

Contribution

It develops a long-term thermal EM exposure model based on Maxwell's equations and bioheat transfer, and proposes an adaptive beamforming algorithm using Lyapunov optimization.

Findings

Effectively stabilizes tissue temperature near safety thresholds

Outperforms conventional schemes with instantaneous exposure constraints

Provides a low-complexity online beamforming solution

Abstract

Electromagnetic (EM) exposure compliance has long been recognized as a crucial aspect of communications terminal designs. However, accurately assessing the impact of EM exposure for proper design strategies remains challenging. In this paper, we develop a long-term thermal EM exposure constraint model and propose a novel adaptive exposure-aware beamforming design for an mmWave uplink system. Specifically, we first establish an equivalent channel model based on Maxwell's radiation equations, which accurately captures the EM physical effects. Then, we derive a closed-form thermal impulse response model from the Pennes bioheat transfer equation (BHTE), characterizing the thermal inertia of tissue. Inspired by this model, we formulate a beamforming optimization problem that translates rigid instantaneous exposure limits into a flexible long-term thermal budget constraint. Furthermore, we develop a low-complexity online beamforming algorithm based on Lyapunov optimization theory, obtaining a closed-form near-optimal solution. Simulation results demonstrate that the proposed algorithm effectively stabilizes tissue temperature near a predefined safety threshold and significantly outperforms the conventional scheme with instantaneous exposure constraints.