## 3 RSMA-Assisted Integrated Sensing and Communication Systems
### Key Challenges for RSMA-Assisted ISAC
#### 3.3.3 Further RSMA-Assisted ISAC Challenges and Considerations  
In order to effectively enable RSMA-assisted ISAC systems, the following technical challenges must be addressed:  
**Energy efficiency**: In RSMA-ISAC systems, there are two key factors for maximizing energy efficiency: the use of low-resolution DACs and the management of interference between communication and radar functions. Low-resolution DACs can significantly reduce power consumption and then bring lower hardware costs [46]. However, reduced resolution can lead to signal quality, making it crucial to optimize power consumption while maintaining performance. Since communication and radar functions share the same hardware, minimizing interference is critical. To control the inter-function and intra-function interference effectively while also enhancing energy efficiency, advanced interference management technique such as RSMA can be applied.  
**Compatibility and interoperability**: Ensuring compatibility and interoperability between radar and communication functions in RSMA-ISAC systems is crucial for seamless integration. Compared to the existing MA technique such as SDMA, RSMA can provide a more flexible solution by using the common stream to manage interference between radar and communication simultaneously [14]. RSMA-based ISAC systems can ensure high-quality communication performance and improved spectrum utilization, enhancing the interoperability and efficiency of the system across various deployment scenarios.  
**Security and data protection**: Note that the security design in RSMA-assisted ISAC networks faces considerable challenges. Although RSMA manages the interference by prop erly dividing the data stream into common and private streams, interference management is particularly critical; while RSMA manages interference by dividing data into common and private streams, controlling interference to prevent unauthorized eavesdropping is quite challenging [47]. Moreover, imperfect CSI plays a vital role in security. Since the precise beamforming relies on accurate channel information, channel estimation errors can increase the risk of interception by unauthorized users. Note that these challenges are major obstacles in simultaneously ensuring security and performance in RSMA-assisted ISAC networks, necessitating the development of advanced algorithms and technologies to overcome these challenges [40].  
**Channel estimation**: Recently, integrating MIMO and ISAC systems has emerged as a promising solution for enhancing both communication and sensing capabilities in ISAC environments [12; 13]. In [12], a CV-based beam focusing technique has been investigated to accurately estimate the position of UE and adjust the beam accordingly, reducing the delays and overhead associated with conventional beam sweeping. In [13], movable antennas are exploited to improve ISAC system performance. Exploiting movable antennas can optimize beamforming gain at target locations by boosting beam gain at specific angles. However, as the position of movable antennas changes, the variation of the channel information also increases, making channel estimation more complex than in fixed antenna systems. To this end, tensor decomposition-based channel estimation can be applied to provide precise channel information with fewer pilots [13]. This enables ISAC systems with movable antennas to achieve better transmission rates and beamforming gains compared to fixed antenna systems.