Abstract

Intelligent transportation systems increasingly rely on High-Occupancy Vehicle (HOV) lane management, creating demand for reliable and privacy-preserving in-cabin occupancy sensing. Cellular Integrated Sensing and Communication (ISAC) has emerged as a promising alternative to camera-based monitoring by enabling detection of occupant movement and physiological activity without capturing visual information. However, electromagnetic shielding from modern vehicle windshields significantly attenuates high-frequency cellular signals, limiting sensing performance inside the cabin. This paper proposes a programmable transmitarray-assisted architecture for mmWave ISAC-enabled in-cabin occupancy sensing. The proposed system leverages programmable spatial focusing to steer cellular signals into specific cabin regions through controllable propagation paths. A cascaded channel model and near-field focusing framework are developed to characterize programmable propagation and spatial sensing behavior in shielded vehicular environments. Simulation and mmWave measurement results demonstrate peak received powers of approximately -44 dBm during beam steering, HPBW values ranging from 16° to 50° for near-field beam focusing, and effective moving-target detection with a clutter suppression ratio (CSR) of 38.66 dB and a target-to-clutter ratio (TCR) of 32.34 dB. These results demonstrate programmable beam steering, near-field focusing, and motion-sensitive sensing at 28 GHz, establishing the feasibility of transmitarray-assisted ISAC sensing for future infrastructure-assisted occupancy monitoring and intelligent transportation applications.

Citation

Cho-Hao Yu, Thomas Yang, Saurabh Parkar, Haofan Cai, Yanjun Pan, Shuqiong Wu, Xiaochan Xue, Yao Zheng, “Programmable Transmitarray-Assisted Near-Field ISAC for In-Cabin Occupancy Sensing,” 2026 IEEE Annual Integrated Sensing and Communication Conference (ISAC), 2026 (accepted).

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Status: Accepted; DOI pending publication.