### Prototype Conceptualization
#### 3.1.1 Purpose Statement
Thus, once the smart backpack prototype has received the VLC data from the indoor lighting infrastructure and the information from the environment perception module, a data processing unit (again an ARM Cortex M7 at 600 MHz board) analyzes it and decides what type of information should be transmitted to the user. Another important module of the smart backpack prototype consists in the block that enables the user to exchange information with the backpack and vice versa. Thus, to request information on certain points of interest, the user uses a gesture sensor which  
Figure 3: Visible light communications-based smart backpack for blind and severely visually impaired persons’ assistance: (**a**) Front and lateral side view; (**b**) Backside view. recognizes predefined gestures and assigns them to a certain request. The request is then analyzed and communicated through the IR transmitter embedded module to the optical transceiver integrated in the indoor lighting infrastructure. The lighting infrastructure module analyzes the request and provides a response which is transmitted using VLC. When the backpack VLC component receives the data, it analyzes it and provides the user with the requested information. The interaction with the user is made through a synthesized voice. Nevertheless, there are situations in which the users might require their hearing for other purposes. For such circumstances, the smart backpack integrates a series of four vibration motors. Two of them are located on the backpack shoulder wrap, one for each arm, and the other two are located on the bottom of the backpack, being in contact with the user's lobar area, left side, and right side. Thus, based on a predefined haptic language that the user has to get used with, information is transmitted. The four vibration motors are also assigned to the four obstacle sensors. More exactly, each obstacle detection sensor, monitoring a certain area around the user, is assigned to one vibration motor. Thus, when an obstacle is detected on the user's front left side (i.e., the user could hit the obstacle with his left shoulder as he moves forward), the vibration motor on the left shoulder wrap begins to vibrate (i.e., distance dependent vibrations). Similarly, to suggest that a wall is located on the left side, the vibration motor in contact with the user's lumbar area is activated (i.e., distance dependent vibrations). In accordance, the 90 cm monitoring range of each sensor is divided in three sectors: 0-30 cm, 30-60 cm, and 60-90 cm. Further on, when an obstacle is detected in a certain area, the vibration motor associated with that sensor generates vibrations of certain frequencies, where vibration frequency is in accordance with the distance toward the obstacle. Thus, when the obstacle is detected at 90 cm, the frequency of the vibrations is low, whereas as the user gets closer to the obstacle, the frequency of the vibrations increases. This versatility allows the system to accommodate a variety of scenarios and user preferences. Figure 3 illustrates the distribution of the modules on the smart backpack. Experimental Testing Procedure, Experimental Results and Discussions concerning the Importance of This Work  
The following section presents the aspects related to the blind persons' assistance smart backpack intensive experimental testing procedure. It details the experimental evaluation method and the associated experimental results, focusing on the individual system components evaluation, as well as on the prototype's evaluation in a complex setup.