Performance Tradeoffs Between Communication and Sensing in Unlicensed ISAC Networks

Integrated sensing and communication (ISAC) networks are envisioned as a key enabler for a variety of applications that demand reliable wireless connectivity along with accurate and robust sensing capability. The unlicensed band is seen as an attractive solution for supporting high data rates and ultra-precise positioning, primarily because of its available broad bandwidth. Meanwhile, the IEEE 802.11 working group has established a new Task Group, namely IEEE 802.11bf, to integrate sensing functionality in current Wi-Fi devices operating in both sub-7 and millimeter wave (mmWave) 60 GHz frequency bands. When sensing and communication share the same spectrum, the communication links in the ISAC networks experience interference from both sensing and communication signals. Therefore, it is crucial to analyze the interference caused by uncoordinated transmission of either sensing or communication signals, so that effective interference mitigation techniques could be put in place. In this paper, we consider an ISAC network operating in unlicensed bands consisting of dual-functional nodes. Each node can operate in sensing and communication modes. To gain access to the shared communication channel, each node performs carrier sense multiple access (CSMA). For this setting, we analyze how the network density affects the sensing and communication performances defined in terms of maximum unambiguous range, target detection delay, and aggregated network throughput, respectively. Using the stochastic geometry approach, we model the interference of the ISAC network in both sub-7 GHz band and 60 GHz mmWave band and derive a closed-form expression for both sensing and communication performance metrics. Finally, we verify our analytical results through extensive simulation.