Target Localization and Performance Trade-Offs in Cooperative ISAC Systems: A Scheme Based on 5G NR OFDM Signals

The integration of sensing capabilities into communication systems, by sharing physical resources, has a significant potential for reducing spectrum, hardware, and energy costs while inspiring innovative applications. Cooperative networks, in particular, are expected to enhance sensing services by enlarging the coverage area and enriching sensing measurements, thus improving the service availability and accuracy. This paper proposes a cooperative integrated sensing and communication (ISAC) framework by leveraging information-carrying orthogonal frequency division multiplexing (OFDM) signals transmitted by access points (APs). Specifically, we propose a two-stage scheme for target localization, where communication signals are reused as sensing reference signals based on the system information shared at the central processing unit (CPU). In Stage I, we measure the ranges of scattered paths induced by targets, through the extraction of time-delay information from the received signals at APs. Then, the target locations are estimated in Stage II based on these range measurements. Considering that the scattered paths corresponding to some targets may not be detectable by all APs, we propose an effective algorithm to match the range measurements with the targets and achieve the target location estimation. Notably, by analyzing the OFDM numerologies defined in fifth generation (5G) standards, we elucidate the flexibility and consistency of performance trade-offs in both communication and sensing aspects. Finally, numerical results confirm the effectiveness of our sensing scheme and the cooperative gain of the ISAC framework.