### Prototype Conceptualization
#### 3.1.1 Purpose Statement
For improved effectiveness, an array of four obstacle-detection modules is distributed on the backpack. Two of these modules are positioned on each lateral side, while the other two are oriented towards the front, as depicted in Figure 3. Within each detection module, there resides a combination of a PIR sensor and an ultrasound sensor. The inclusion of these two distinct sensor types is motivated by their high compatibility with each other, which serves to reinforce the reliability of the information provided to the user. These obstacle-detection modules are strategically placed, each encompassing a 60-degree angle, resulting in a 240-degree coverage. Each module has a detection range set at 90 cm. Although longer ranges up to 250 cm could be used, it was considered that the most relevant information is the one from the immediate vicinity. Choosing a wider range can lead instead to situations in which all the sensors are constantly detecting certain obstacles, providing the user with too much information, which in turn can be rather distracting and less effective for the user. Anyway, the obstacle detection range can be further increased up to more than 250 cm if the user requires it. The obstacle detection modules are also vertically adjustable ensuring adaptability to the user's specific needs. The core function of these modules is to identify and alert the user regarding the presence of objects or individuals obstructing their path, thereby enhancing safety and facilitating smooth navigation. The environment perception unit also englobes a gyroscopic sensor and an accelerometer. The gyroscopic sensor is used \begin{table}
\begin{tabular}{c c l} \hline \hline  & \(\bullet\) & 4 \(\times\) 9 W LED tubes VLC transmitter integrated as part of the indoor lighting system; \\ _Lighting infrastructure_ & \(\bullet\) & Luminaire height: 3.5 m from the floor; \\ _transmitter parameters_ & \(\bullet\) & Compatible with simultaneous data transmission and light dimming in the 1–99\% interval; \\  & \(\bullet\) & Compatible with digital but also analog data transmission; \\ \hline  & \(\bullet\) & Asynchronous communication; \\  & \(\bullet\) & On-Off Keying (OOK) modulation with Manchester coding capability, with data rates between 10 and 250 kb/s; \\  & \(\bullet\) & VPPM modulation capability with variable duty cycle between 1\% and 99\%, providing data rates between 10 and 100 kb/s (100 kb/s for these tests); \\ _Communication parameters_ & \(\bullet\) & BFSK with NRZ coding, working at a 10 kb/s data rate; \\  & \(\bullet\) & Capability with variable duty cycle between 1\% and 99\%, providing data rates between 10 and 100 kb/s (100 kb/s for these tests); \\  & \(\bullet\) & Real-time data processing; \\ \hline  & \(\bullet\) & \(\pm 53^{\circ}\) reception angle (field-of-view); \\  & \(\bullet\) & PDA100A2 PIN photodiode optical detector; \\  & \(\bullet\) & Real time data processing based on pulse width measurement; \\  & \(\bullet\) & High optical noise resilience; \\  & \(\bullet\) & Improved mobility due to adaptive gain; \\  & \(\bullet\) & Real-time BER with no forward error correcting protocols. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of the VLC parameters. to monitor users' orientation, in order to properly guide them in the right direction. As the chances of falling are significantly higher for blind persons, the accelerometer is envisioned to identify potential situations in which users' have fallen and/or are injured. As one can see, while the communication component excels in indoor VLC-covered areas, the obstacle-detection component complements it by providing supplementary information. More importantly, it also extends its utility beyond the limits of VLC-enabled indoor environments, making it useful for both indoor and outdoor settings.