### Experimental Results
#### 4.2.2 Experimental Results for the Obstacle Detection Component Evaluation
Nevertheless, in [44], a limited 25-85 dimming range was demonstrated, while providing a \(10^{-3}\) BER, and communication range below 1 m. Furthermore, demonstrating the system's ability to maintain the data link even for a 1% duty cycle, emphasizes the concept's compatibility with energy saving applications and with the current preoccupations for energy efficiency. Another important contribution of this work comes from the fact that unlike most of the works that promote the development of a new notion or of a new technology, this work delivers the integration of the proposed concept into a functional device, together with an extended experimental investigation that demonstrates the concept's utility in a relevant use case. Thus, this work not only introduces the use of the VLC technology in severely visually impaired and blind persons' assistance, but it provides a relevant experimental demonstration for its utility. Therefore, although the proposed concept is not yet a commercial device (i.e., a TRL 10 product), it provides a TRL 6 product, providing the basis for future enhancements. Thus, this work aimed to make the transition from fundamental research to experimental research, contributing to the deployment of the VLC technology in new applications. Hence, although there are several other works that analyzed the use of VLC in blind persons' assistance, the prototype presented in this article is one of the most advanced, benefiting from a more realistic integration, from a more intensive testing and from an overall enhanced design. Furthermore, to improve its capacity and to enable its use in areas with no VLC coverage, the smart backpack concept also integrates environment perception sensors that provide a 240\({}^{\circ}\) degree scanning around the user, enabling the detection of obstacles located in the users' path. Additionally, these sensors significantly improve the trajectory and travel time of visually impaired users, instilling confidence and reducing the risk of collisions with other persons or with obstacles, reducing in turn the chances of accidents during the walk. Thus, as the experimental results have confirmed, the use of this sensor fusion enabled the user to maintain a straighter trajectory and to improve its confidence, resulting in in shorter walking times. An important aspect that should be clarified is related to the functionality of the proposed solution in multiple lighting devices setup. From this perspective, the current version of the prototype did not address the issues associated with multiple lighting devices. Nevertheless, the indoor VLC literature has widely addressed these issues and it was able to find the proper solutions that allow user mobility, provide the hand-over mechanisms between multiple light sources, and enable multiple-users resource sharing [45; 46; 47]. Consequently, it can be considered that user movement and the synchronization between multiple lighting devices are not that problematic. One limitation of the proposed solution comes from the relatively low data rates. For comparison, record data rates in indoor VLC applications go up to a few tens of Gb/s [48]. Although the experimental results showed that the prototype is compatible with user movement, the mandatory Line of Sight (LoS) condition imposed for VLC systems represents probably the most important limitation of the concept. This fact could lead to possible communication blockage in certain circumstances when the user is no longer within the VLC luminaire coverage. In such situations, the user will have to rely on the previously received data, and on the obstacle detection sensors until the link is reestablished. Overall, it can be considered that the experimental evaluation of each of the smart backpack components and its evaluation in a complex situation has confirmed the benefits of the proposed solution, as well as the benefits resulting from multiple technologies and data fusion.