# Key Technologies for 6G-Enabled Smart Sustainable City
## 4 Key Candidate Technologies for Future SSC
### Prime Technologies for SSC
#### 4.2.5 Integrated Sensing and Communication  
Progress in IoT services, including AI, smart cities, and autonomous driving, relies on the advanced sensing, communication, and computation capabilities in next-generation wireless networks. The growing need for an integrated sensing and communication system arises from its potential to improve both functionalities and minimize the use of wireless resources via full cooperation. Moreover, integrated systems can boost efficiency in system design by sharing hardware components [108; 109]. The high-resolution sensing, imaging, and environmental reconstruction capabilities of ISAC systems are crucial for facilitating diverse applications in smart cities. These capabilities have a significant impact on key areas like environmental monitoring, traffic management, energy efficiency, and the implementation of improved safety and security measures [54; 110]. In accordance with the smart city paradigm, the strategic utilization of wireless resources aims to optimize network efficiency, reduce energy consumption, and promote the adoption of sustainable practices.The application of the ISAC system is depicted in Figure 6.  
While managing interferences between communication and sensing functionalities is a key challenge for ISAC systems, recent research has shown that the RSMA technique can effectively achieve flexible and robust interference management between communication and sensing, as well as among communication users [111]. In addition, the following technical challenges should be addressed to exploit the full benefits of ISAC in SSC. **Joint waveform design**: The waveform design approach must involve consideration of all the communication and sensing requirements essential to support ISAC. The main goal of communication is to maximize spectral efficiency, whereas sensing aims to enhance estimation resolution or accuracy. In ISAC systems, it is desirable to share a single set of common transmission waveforms for both communication and target sensing. Therefore, a joint waveform design framework needs to be developed to improve the network throughput and estimation performance. **Doppler effect**: ISAC has been widely employed in LEO satellite communication systems. The high velocity of LEO satellites (approximately 7.6 km/s at an altitude of 600 km) induces a substantial Doppler shift in radio links between ground terminals and NTN devices. A possible solution to the Doppler issue is to leverage machine learning techniques for accurate channel estimation and compensation of frequency-selective and time-varying channel effects. It is essential to mitigate the Doppler effects by carefully selecting sensing parameters and estimating communication channels [112]. **Personal data breach**: Next-generation communication systems will be designed to offer a variety of IoT-enabled broadband services. As the number of connected devices increases, ensuring the security of SSC networks becomes increasingly crucial. For example, the openness of wireless sensing allows attackers to eavesdrop on the CSI of the target, potentially leading to a breach of the user's personal information and disruption of legitimate communication [113]. The security-related transmission/reception schemes in ISAC systems have not yet been extensively studied. **Fixed bandwidth**: ISAC systems perform detection and communication functions in the same frequency band by sharing common hardware. The 3 rd Generation Partnership Project (3 GPP) has defined two frequency ranges for new wireless technologies: one supporting up to 100 MHz and the other allowing for a maximum of 400 MHz. Although this resolution is sufficient for typical detection tasks (range resolutions of 1.5 m and 0.375 m), it falls short when higher precision and location information are required, as in the case of autonomous vehicles. Developing signal processing techniques that can enhance detection performance and range resolution becomes crucial when the available frequency bandwidth is limited [114].