## 4 Development and Validation of the Platform
### Application Performance
#### 4.4.2 QoE Metrics and Measurement Results  
Next, we present the analysis of the Quality of User Experience obtained from a survey conducted among 53 participants who tested the Digital Twin application prototype featuring the immersive remote driving of two robots. The tests took place in high-density city environments, with a distance of around 7 km between the robots and the cockpits. The assessment focused on various factors, such as presence, engagement, control, sensory integration, and cognitive load, whose results help to validate the QoS offered by the platform for supporting Digital Twin applications in real-life scenarios.  
The metrics for assessing presence indicate a high level of perceived immersion among participants. Specifically, 97.9% of the participants rated their sense of presence at level 4 or above, suggesting that the system successfully created a convincing remote environment. This strong sense of presence is critical for applications requiring teleoperation, as it directly impacts the operator's situational awareness and effectiveness.  
Regarding engagement, a combined 95.8% of participants rated their engagement in the teleoperation experience at level 4 or above. This indicates that the system's immersive elements, such as real-time video streaming and responsive controls, were effective in maintaining user interest and focus throughout the demonstration.  
The participants' perceptions of control over the remote robot were also high, with 75% of them rating their control experience at level 4 or above. This suggests that the system's teleoperation interface was intuitive and responsive, which is crucial for real-time control scenarios where precision and responsiveness are required.  
Sensory integration, which measures the effectiveness of combining visual and haptic feedback, received not-so-favorable ratings and is currently in need of improvement. Only 39.6% of participants rated it at level 4 or 5, indicating that the multimodal feedback provided an experience that was not entirely cohesive. Effective sensory integration is vital for enhancing the user's interaction with remote systems, especially in scenarios requiring fine-grained control and quick reaction times. However, most participants were not accustomed to the inclusion of haptic feedback in a remote driving scenario.  
The cognitive load associated with the teleoperation task was assessed to understand how mentally demanding the experience was for participants. While 33.3% rated the task as highly demanding (level 5), a significant proportion (22.9%) found it relatively manageable (level 2). These results highlight the system's capability to balance complexity and usability, ensuring that users can focus on control and interaction without being overwhelmed by the cognitive demand.  
The results suggest that, while optimizing sensory integration and cognitive load is required for complying with less experienced users, the platform is able to successfully offer the required QoS and QoE to support generic Digital Twin applications (as well as immersive and interactive experiences).