Exploring ISAC: Information-Theoretic Insights

This article reviews results from the literature illustrating the bottlenecks andtradeoffs of integrated sensing and communication (ISAC) through the lens of informationtheory, thus offering a distinct perspective compared to recent works that focus on signalprocessing, wireless communications, or other related overviews. Different models andscenarios are considered and compared. For example, scenarios where radar sensing isperformed at the communication and radar transmitter (mono-static ISAC) and scenarioswhere the radar receiver differs from the radar transmitter (called bi-static radar). Similarly,we discuss ISAC bottlenecks and tradeoffs both in slowly-varying environments wherethe main sensing target is described by a single parameter and accordingly, sensing performanceis described by detection error probabilities, as well as in fast-varying environments,where the sensing targets are described by vectors and thus vector-valued performance measuressuch as average distortions like mean-squared errors are used to determine sensingperformances. This overview article further also considers limitations and opportunities innetwork ISAC environments, such as collaborative or interactive sensing, and the influenceof secrecy and privacy requirements on ISAC systems, a line of research that has receivedgrowing interest over the last few years. For all these scenarios, we provide and discussprecise models and their limitations and provide either bounds or full characterizationsof the fundamental information-theoretic performance limits of these systems. Furtherextensions as well as important open research directions are also discussed.