### Prototype Conceptualization
#### 3.1.1 Purpose Statement
Therefore, adding extra features to a product can make it cost-efficient if multiple users' needs are satisfied. _From a developer's perspective_, the Visible Light Communications technology imposes a series of constraints. As previously mentioned, VLC assumes the use of the LED lighting equipment for simultaneous illumination and data transmission. _Data transmission as a secondary feature:_ Because the digital information sent through an existing lighting system is a secondary feature, it must not affect the primary function, as an illumination device, in any way. Therefore, the use of the VLC technology in the blind-assistance purpose should respect the following principles:  
* VLC should not impact the existing lighting infrastructure from a hardware point of view or should have a minimum impact;
* VLC function should not affect lighting from a regular user visibility point of view, meaning that the same lighting intensity should be provided; thus, light intensity should not be increased in order to improve the Signal-to-Noise Ratio (SNR), nor it should be decreased unnecessarily;
* VLC should not generate visible or perceivable flickering;
* When light dimming is necessary, data transmission should be available. _Communication coverage:_ Another aspect that should be considered is related to the coverage area. In order to be useful and safe, the VLC system should have the potential to provide wide area coverage. Therefore, while considering the existing distribution of the lighting devices within the space, the prototype should be able to ensure VLC data transmission for the entire envisioned area. _User-centered data distribution:_ In order to be effective in blind user assistance, the solution should be able to localize the user, in order to transmit location specific information. Nevertheless, different from IoT applications or from robot control applications where centimeter precision is required, in this case, high precision localization is less important, as the main objective is to have an estimation of the user's position. Visible Light Communications-Based Smart Backpack for Visually Impaired Persons: Implementation Process  
Within the upper-described context, this ongoing project was initiated with the purpose of designing, developing, and experimentally testing a novel visually impaired and blind assistance device that is _discret_, _versatile_, _user-friendly_, and _cost-efficient_. The main aim of the project is to create a device that seamlessly integrates multiple functions into an item that does not draw attention to the user's impairment. To achieve this goal, the proposed concept takes the form of an everyday backpack, making it useful already. This design approach offers ample space for concealing the various sensors required for enhanced functionality, ensuring that the final product supports the aforementioned requirements of discretion, utility, and multi-purpose use. The schematic of the proposed design is illustrated in Figure 1. As one can see, in addition to the basic backpack, the system consists of five main blocks. The first block is the _energy power block_. For improved utility and versatility, the concept uses a 10 W PhotoVoltaic (PV) panel that has the purpose of improving the energy-efficiency and the autonomy of the system. The resulting electricity/energy is stored in a 5V/20,000 mAh power bank, which is used to power the smart backpack's other blocks. However, for improved utility, the user can also recharge thier personal devices, such as smartphones or smartwatches, through several USB ports. The most important component of the concept is the _optical wireless communications block_. To facilitate data exchange with the indoor lighting system, the smart backpack prototype employs two optical transceivers positioned on the upper side, more precisely on the backpack braces. On the other side of the VLC channel, the infrastructure-integrated wireless communication component includes an optical transceiver fitted into the indoor lighting network.