A Survey on Fundamental Limits of Integrated Sensing and Communication (2104.09954v2)

Abstract: The integrated sensing and communication (ISAC), in which the sensing and communication share the same frequency band and hardware, has emerged as a key technology in future wireless systems. Early works on ISAC have been focused on the design, analysis and optimization of practical ISAC technologies for various ISAC systems. While this line of works are necessary, it is equally important to study the fundamental limits of ISAC in order to understand the gap between the current state-of-the-art technologies and the performance limits, and provide useful insights and guidance for the development of better ISAC technologies that can approach the performance limits. In this paper, we aim to provide a comprehensive survey for the current research progress on the fundamental limits of ISAC. Particularly, we first propose a systematic classification method for both traditional radio sensing (such as radar sensing and wireless localization) and ISAC so that they can be naturally incorporated into a unified framework. Then we summarize the major performance metrics and bounds used in sensing, communications and ISAC, respectively. After that, we present the current research progresses on fundamental limits of each class of the traditional sensing and ISAC systems. Finally, the open problems and future research directions are discussed.

• The paper presents a comprehensive survey of ISAC by analyzing fundamental limits using metrics like CRB, EFIM, and AF across diverse radar and localization setups.
• It classifies ISAC systems into device-free and device-based categories, detailing differences in radar sensing and wireless localization techniques.
• The study highlights potential performance enhancements through integrated system designs and calls for further research on adaptive coding and IRS-assisted scenarios.

Fundamental Limits of Integrated Sensing and Communication

The paper “A Survey on Fundamental Limits of Integrated Sensing and Communication” presents a detailed examination of Integrated Sensing and Communication (ISAC), focusing on the technological requirements, system classifications, and theoretical boundaries. ISAC systems promise to effectively use spectrum resources by combining sensing and communication functions, addressing the growing demands of 5G and beyond.

Overview of ISAC

The authors highlight ISAC as essential for the next-generation wireless systems due to the parallels between emerging technological capabilities and the demands of applications such as autonomous vehicles, radar sensing, and Wi-Fi sensing. They provide a classification of ISAC systems into device-free and device-based categories. Device-free systems primarily involve radar sensing, while device-based systems focus on wireless localization.

Device-Free Sensing

The paper provides a rigorous analysis of phased-array radar, MIMO radar, and phased-MIMO radar in mono-static and bi-static configurations. The authors present the Cramer-Rao Bound (CRB) and Ambiguity Function (AF) to evaluate the estimation accuracy of time delay, direction of arrival (DOA), and Doppler shift.

Device-Based Sensing

For device-based sensing, the focus is on TOA, AOA, and RSS-based localization techniques, emphasizing the importance of effective bandwidth, SNR, and multipath effects. The authors derive fundamental limits using metrics like the EFIM and CRB, offering insights into the impact of network topology and environmental conditions on localization accuracy.

ISAC Channels

A significant portion of the paper is devoted to the information-theoretic modeling of ISAC systems. For device-free ISAC, they explore various channel configurations, such as multiple access and broadcast channels, examining capacity-distortion tradeoffs. For device-based ISAC, the paper of communication and localization synergy highlights the potential performance enhancements achievable through integrated system designs.

Implications and Future Directions

The authors stress that understanding the fundamental limits is crucial to bridging the gap between current technologies and theoretical performance bounds. They call for further studies, especially on emerging scenarios like IRS-aided ISAC and complex network topologies, taking into account practical considerations such as imperfect CSI and frequency offset.

Future developments might include enhanced joint coding strategies and adaptive resource allocation schemes to optimize performance tradeoffs, potentially leading to more robust and efficient ISAC implementations.

Conclusion

This paper provides a comprehensive review of the fundamental limits of ISAC, offering a valuable foundation for subsequent research. Future work should aim at developing tighter bounds and more refined models, particularly under real-world constraints, to advance the performance and practicality of ISAC systems.