5G ISAC-Based UAV Detection and 3-D Tracking Using Uplink Sounding Reference Signals on an End-to-End O-RAN Simulation Testbed

Integrated Sensing and Communication (ISAC) lets cellular infrastructure serve communication users and sense on the same waveform. We present an end-to-end O-RAN simulation testbed for 5G ISAC targeting low-altitude UAV detection and 3-D tracking, built from open-source components: OpenAirInterface, FlexRIC and Sionna RT, in which the NR Uplink Sounding Reference Signal is repurposed as a passive radar waveform: a PHY-layer sensing stage inside the gNB produces detections that reach an Extended Kalman Filter tracking xApp over a custom E2 service model, with no change to the NR standard and no dedicated sensing waveform. A single bistatic pair leaves elevation unobservable, so the tracker needs a height prior; we remove it two independent ways and measure both - a planar receive array supplying a vertical aperture, and a second transmitter supplying range diversity. Both live results corroborate an offline ray-traced study of the same estimator, which converges from a deliberately wrong initial altitude to 1.8 m RMSE at a consistent filter, so altitude observability is established both in the signal-processing chain and end to end through the live stack. Detection coverage is preserved under a concurrent 10 Mbps uplink communications load.