Cooperative Monostatic and Bistatic Measurements for Low-Altitude UAV ISAC: System Implementation and Channel Characterization.

Low-altitude unmanned aerial vehicle (UAV)-integrated sensing and communication (ISAC) channels are governed by rapidly evolving multipath. These dynamics arise from UAV motion, air-ground geometry, and scene-dependent scatterers, yet field evidence comparing monostatic and bistatic sensing links remains limited. We develop a cooperative monostatic-bistatic measurement system for low-altitude UAV ISAC channel sounding. The system integrates a UAV-borne sensing node, a ground node, synchronized acquisition, and an offline processing chain. It enables UAV-borne monostatic sensing and air-ground bistatic sensing to be measured within the same low-altitude urban scenario. A field measurement campaign is conducted along a representative route containing buildings, trees, roadside facilities, and open ground. From the measured in-phase/quadrature (IQ) data, the system extracts channel impulse responses (CIRs) and power delay profiles (PDPs) as primary measurement products. Delay-Doppler processing, multipath-component extraction, and trajectory analysis are applied to compare link-dependent propagation behavior under matched environmental conditions. The measurement results demonstrate that the proposed platform can jointly capture monostatic and bistatic ISAC channel responses and support controlled and synchronized low-altitude UAV channel measurement experiments. This system provides an experimental basis for UAV ISAC channel modeling, measurement-platform assessment, and subsequent sensing algorithm evaluation.