## 5 Conclusions  
In this paper, the optimization scheme of the sum-rate for the RIS-assisted RSMA in MU-MIMO system with a reconfigurable impedance network connected by the group was proposed. First, the scattering matrix was successively optimized for each group, which was grouped by the RIS elements with the largest channel gain to the scheduled users. Then, the optimization of the RS power-splitting ratio was iteratively performed based on FP. The proposed scheme is adaptive to each UE channel and flexible in managing the interference. The simulation results showed that the proposed system had a higher sum-rate than the conventional RIS-assisted SDMA. Additionally, it can be observed that proposed system is more energy efficient and can support the users up to the number of groups with appropriate performance. Therefore, the proposed RIS-assisted RSMA scheme can be used effectively in the future B5G and 6G systems. Conceptualization, M.-A.K., H.-D.K. and K.-H.S. ; methodology, M.-A.K. and S.-G.Y. ; validation, M.-A.K. and H.-K.S. ; investigation, M.-A.K. ; resources, M.-A.K. ; data curation, M.-A.K. ; writing--original draft preparation, M.-A.K. ; writing-review and editing, M.-A.K. and H.-K.S. ; visualization, M.-A.K. ; supervision, Y.-H.Y. and H.-K.S. ; project administration, Y.-H.Y. and H.-K.S. ; funding acquisition, H.-K.S. All authors have read and agreed to the published version of the manuscript. This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020R1A6A1A03038540). This research was supported by the R&D Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF-2020M3C1C1A02086428). Not applicable. The authors declare no conflict of interest. Figure 7: Sum-rate versus the number of users with \(N_{G}=8\) and \(N_{I}=16\). * [PERSON] et al. (2021) [PERSON]; [PERSON]; [PERSON]; [PERSON] Rate-Splitting Multiple Access for Downlink Multiuser MIMO: Precoder Optimization and PHY-Layer Design. _IEEE Trans. Commun._**2021**, _70_, 874-890. [CrossRef]
* [PERSON] et al. (2022) [PERSON]; [PERSON]; [PERSON]; [PERSON] Rate-Splitting Multiple Access for 6G--Part III: Interplay With Reconfigurable Intelligent Surfaces. _IEEE Commun. Lett._**2022**, _26_, 2242-2246. [CrossRef]
* [PERSON] et al. (2016) [PERSON]; [PERSON]; [PERSON]; [PERSON] A Rate Splitting Strategy for Massive MIMO With Imperfect CSIT. _IEEE Trans. Wirel. Commun._**2016**, _15_, 4611-4624. [CrossRef]
* [PERSON] (2011) [PERSON] _Microwave Engineering_; John Wiley & Sons: Hoboken, NJ, USA, 2011. * (20) 3 GPP, Sophia Antipolis, France. Study on Channel Model for Frequency Spectrum Above 6 GHz; rep. 38.900 ed. 2017. Available online: [http://www.3 gpp.org/DynaReport/38900-CRs.htm](http://www.3 gpp.org/DynaReport/38900-CRs.htm) (accessed on 10 April 2023). * [PERSON] et al. (2018) [PERSON]; [PERSON]; [PERSON]; [PERSON] Millimeter-Wave Communications: Physical Channel Models, Design Considerations, Antenna Constructions, and Link-Budget. _IEEE Commun. Surv. Tutor._**2018**, _20_, 870-913. [CrossRef]
* [PERSON] and [PERSON] (2016) [PERSON]; [PERSON] Sum-Rate Maximization for Linearly Precoded Downlink Multiuser MISO Systems with Partial CSIT: A Rate-Splitting Approach. _IEEE Trans. Commun._**2016**, _64_, 8447-8461. [CrossRef]
* [PERSON] and [PERSON] (2021) [PERSON]; [PERSON]; [PERSON] Analysis of Hierarchical Rate Splitting for Intelligent Reflecting Surfaces-Aided Downlink Multiuser MISO Communications. _IEEE Open J. Commun. Soc._**2021**, \(2\), 785-798. [CrossRef]
* [PERSON] et al. (2015) [PERSON]; [PERSON]; [PERSON] Rate Analysis of Two-Receiver MISO Broadcast Channel With Finite Rate Feedback: A Rate-Splitting Approach. _IEEE Trans. Commun._**2015**, _63_, 3232-3246. [CrossRef]
* [PERSON] et al. (2016) [PERSON]; [PERSON]; [PERSON] Overloaded multiuser MISO transmission with imperfect CSIT.