Next-generation wireless networks (such as beyond 5G (B5G) and 6G) have been envisioned as key enablers for many emerging applications. These applications demand high-quality wireless connectivity as well as highly accurate and robust sensing capability. Among many visionary assumptions about B5G/6G networks, a common theme is that sensing will play a more significant role than ever before.

While the speculative study for future wireless systems has just begun, the technological trends clearly show that we are ready to embrace the new sensing functionality in the forthcoming B5G and 6G eras. Indeed, sensing and communication (S&C) systems are both evolving towards higher frequency bands, larger antenna arrays, and miniaturization, thereby becoming increasingly similar in terms of hardware architectures, channel characteristics, and signal processing. This offers an exciting opportunity of implementing sensing by utilizing wireless infrastructures, such that future networks will go beyond classical communication and provide ubiquitous sensing services to measure or even to image surrounding environments. This sensing functionality and the corresponding ability of the network to collect sensory data from the environment are seen as enablers for learning and building intelligence in the future smart world, and may find extensive usage in numerous location/environment-aware scenarios. To name but a few, vehicle-to-everything, smart home, smart manufacturing, remote sensing, environmental monitoring, and human-computer interaction, as shown in the above figure. Towards that end, there is a strong need to jointly design the S&C operations in B5G/6G networks, which motivates the recent research theme of Integrated Sensing and Communications (ISAC).

The information processing between S&C shows a striking distinction. Sensing collects and extracts information from noisy observations, while communication focuses on transferring information via specifically tailored signals and then recovering it from a noisy environment. The ultimate goal of ISAC is to unify these two operations and to pursue direct tradeoffs between them as well as mutual performance gains. On the one hand, ISAC is expected to considerably improve spectral and energy efficiencies, while reducing both hardware and signaling costs, since it attempts to merge sensing and communication into a single system, which previously competed over various types of resources. On the other hand, ISAC also pursues a deeper integration paradigm where the two functionalities are no longer viewed as separate end-goals but are co-designed for mutual benefits, i.e., via communication-assisted sensing and sensing-assisted communication.