## 4 Potential Research Directions of RSMA-Assisted ISAC Systems
### Non-Terrestrial Networks  
Since terrestrial networks (TNs) are not deployed in remote areas, such as deserts and oceans, NTNs can effectively provide high-speed communication services to such  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Prime Technology** & **Key Features** & **Future Application Scenarios** \\ \hline \multirow{4}{*}{NTN} & - Improved resource utilization [48] & - Efficient management and detection of beam interference between communication users [48] \\  & - Provides wide coverage [50] & - Real-time communication and sensing capabilities in disaster response systems [52] \\ \hline \multirow{4}{*}{RIS} & - Improved energy efficiency [53] & - Enable communication and localization in smart cities [55] \\  & - Iterative optimization for SNR maximization [39] & - Intelligent control of wireless channels at a low cost [39] \\ \hline \multirow{2}{*}{MmWave and THz} & - Pilot overhead reduction via compressed sensing [56] & - Enhanced communication and detection accuracy [57] \\  & - Boosts reliability via beamforming [17] & - Provision of high-quality communication services through onboard units [59] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Four prime technologies for RSMA-assisted ISAC.  
areas. NTN terminals are classified into satellites, high-altitude platform stations (HAPSs), and unmanned aerial vehicles (UAVs) based on their flight altitude. Satellite terminals are further divided into geostationary orbit (GEO), medium earth orbit (MEO), and LEO based on their orbital altitude. Recently, LEO satellites have attracted interest from both academia and industry because of their high transmission rates and flexibility. In recent years, the combination of LEO and ISAC has increased throughput by managing both sensing and communication [11].  
Note that since LEO satellites offer significantly reduced latency and path loss compared to GEO and MEO satellites, they have led to explosive research in this area [60]. However, LEO satellites, due to their higher mobility compared to other satellites or TNs, face challenges such as Doppler shifts and imperfect CSI. Among the existing multiple access techniques, RSMA can be an effective means of satisfying users' QoS even under imperfect CSI conditions, and it has been shown to outperform other MA technologies in satellite networks [61].  
Most of the literature on RSMA has been focused on TNs. In [48], RSMA was applied in LEO-ISAC systems to efficiently manage and detect beam interference among communication users in LEO-ISAC systems. Figure 5 illustrates an overview of the RSMA-assisted LEO-ISAC systems. Note that since a high round-trip propagation delay results in a severe echo path loss in a monostatic ISAC structure, a bistatic ISAC can be a promising scenario where a radar receiver is separated from the transmitter. In [49], bistatic RSMA-assisted LEO-ISAC systems have been investigated to reduce radar echo path loss.  
Further, with recent technological advances, UAVs are being widely used in various applications such as communication, search and rescue, and remote monitoring. Most of the literature on UAV-assisted ISAC research has focused on channel modeling and performance, utilizing ISAC to support both communication and sensing capabilities [50]. In [51], the collaborative networking system for an intelligent UAV cluster was investigated using UAVs and ISAC to improve sensing accuracy. In [62], the resource allocation through trajectory or deployment optimization was investigated in UAV-assisted ISAC systems. Recent studies [63] have demonstrated that RSMA in UAVs outperforms NOMA in terms of energy efficiency. In [64], the initial framework and maximized energy efficiency in a radar detection and communication system were proposed. Recently, ref. [52] introduced an RSMA-assisted ISAC system model in emergency UAV systems, demonstrating higher improved weighted sum rate (WSR) performance.  
Figure 5: RSMA-assisted LEO-ISAC systems.