Real-Time Symbol-Domain OFDM Radar in an OpenAirInterface 5G Base Station With O-RAN Sensing Services

Abstract

This paper presents a real-time orthogonal frequency-division multiplexing (OFDM) radar embedded in the OpenAirInterface (OAI) 5G base-station process. The radar removes communication symbols by regularized element-wise division and performs range-Doppler processing and ordered-statistic constant-false-alarm-rate detection online without modifying the 5G waveform. The implemented system provides 2.57 m nominal range resolution and 0.28 m/s velocity resolution. Hardware measurements identify and mitigate several implementation-specific limitations, most notably a deterministic carrier-dependent transmit-receive phase rotation on a Universal Software Radio Peripheral (USRP) X300. Selecting a tuning-grid-aligned carrier improves mean-removal clutter suppression from -16.4 dB to 38.0 dB and reduces coherent-integration loss from 19.81 dB to 0.27 dB. The measured processing gain closely agrees with its predicted value. Instrumented worker timing confirms real-time operation, with a conservative 58.4 percent utilization bound and no dropped soundings. A custom E2 service model, E2SM-RADAR, exports detections and a compact slow-time product to a near-real-time RAN Intelligent Controller. Live end-to-end operation demonstrates reliable delivery and supports controller-side tracking, micro-Doppler analysis, and classification. With a commercial user equipment connected on the same carrier, measurements show no measurable difference in downlink throughput estimate with sensing enabled, while the radar sensing bandwidth follows the scheduler allocation. Video demonstration can be found in youtube: youtu.be/GaYAcTJ8RKI