# Optimization of RIS-Assisted 6G NTN Architectures for High-Mobility UAV Communication Scenarios
## 4 Joint Optimization Framework for RIS Configuration and UAV Mobility
### Performance Evaluation and Trade-Off Analysis
#### 4.3.4 Latency
Environmental factors such as interference, multipath propagation, and deployment conditions play a crucial role in throughput performance across different scenarios. #### 5.1.3 Energy Efficiency [Mbps/W]

**Trend:** The urban and indoor scenarios show a consistent increase in energy efficiency as the number of RIS elements increases, highlighting the effectiveness of RIS in these environments. The rural scenario starts by increasing while the highway scenario starts by decreasing but both scenarios later maintain steady energy efficiency across different \(M\) values, indicating stable power utilization. The emergency scenario starts with relatively high energy efficiency but this gradually declines, potentially due to increased power consumption outweighing performance gains. **Interpretation:** The increase in energy efficiency for the urban and indoor scenarios suggests that RIS deployment can significantly improve power utilization in challenging environments. However, the decreasing trend in the emergency scenario emphasizes the trade-off between increasing RIS elements and diminishing energy returns under extremeconditions. Balancing performance and energy efficiency is critical, especially for NTN systems operating under diverse environmental constraints. #### 5.1.4 Outage Probability [%]

**Trend:** The urban scenario initially has a moderate probability of outages, but this improves steadily as the number of RIS elements \(M\) increases. The rural scenario starts with a lower probability of outage but it increases over time, surpassing the urban scenario in the higher-\(M\) range. The highway scenario remains relatively stable with slight variations. The indoor scenario exhibits a consistent probability of outage, showing little impact from increasing \(M\). The emergency scenario begins with the highest outage probability which gradually decreases, indicating some improvement but still maintaining a relatively higher outage compared to other environments. **Interpretation:** Increasing the number of RIS elements generally helps reduce outage probability in urban and emergency environments. However, rural environments experience an increasing outage trend, possibly due to changing propagation conditions or interference. The indoor environment remains unaffected, suggesting that RIS elements may have a limited impact in highly controlled settings. It is important to note that the outage probability levels observed in the evaluated scenarios remain above 10%, which is not sufficient for ultra-reliable low-latency communication (URLLC) or other mission-critical applications. This is mainly due to practical system constraints, including imperfect CSI acquisition, rapid CSI aging caused by high Doppler shifts, limited RIS quantization resolution, and mobility-induced phase misalignment. Future work will focus on improving the accuracy of the real-time CSI estimation, integrating predictive Doppler compensation, and developing faster RIS reconfiguration strategies to reduce the probability of outages towards reliability-critical targets. #### 5.1.5 Latency [ms]

**Trend:** Latency generally decreases in the urban and emergency scenarios as \(M\) increases, indicating an improvement in response with more RIS elements. The rural scenario maintains a low latency for all \(M\) values, whereas the indoor and highway scenarios show a slight increase in latency as \(M\) increases, possibly due to processing overhead. **Interpretation:** RIS-assisted NTN systems effectively manage latency, with notable improvements in the urban and emergency scenarios as RIS elements increase. While some scenarios (e.g., indoor) experience slight latency growth, the overall impact remains within acceptable limits for low-latency applications like vehicular and emergency networks. The results of this study provide valuable insights for the design and implementation of RIS-assisted NTN systems, highlighting the potential of RIS technology to significantly improve communication performance in challenging environments.