VLC a.k.a Visual Light Communication Indoor Navigation systems are part of an inclusive, smart technology future for the visually impaired. As of 2018, there are about 1.3 billion people worldwide that live with vision impairment, and 37 million that are blind. Many blind people rely on their senses and memorization of furniture placement and floor layouts to navigate indoors. However, adjusting can prove difficult in unfamiliar buildings they have never been to. From business buildings to new homes, simple braille signs are not always the easiest to find or rely on. To help the visually impaired better navigate indoor places, there is a relatively new invention of Li-Fi (Light Fidelity) aka VLC (Visual Light Communication) using LEDs. VLC navigation systems rely on special Li-Fi LEDs and GPS-like software systems.
The Concept of VLC Navigation System
VLC navigation systems are based on a technology called Li-Fi. To describe how this works, Li-Fi utilizes the visible light spectrum and LED bulbs. These bulbs send data encoded through certain patterns and short pulses of light that are not noticeable to the naked eye. Li-Fi is perfect for indoor usage where satellite and other RF signals may not reach, and where signals communicate short distances. It is also advantageous over other data systems because it is cheap and energy efficient. Thus, Li-Fi LEDs are perfect for transmitting and receiving signals in VLC navigation systems.
New research and development has been going into incorporating Li-Fi systems into smart home and building technologies. Specifically, these smart systems are designed to enable voice commands to get information about routes and orientation. Similar to virtual assistants like Siri from Apple or S-Voice from Samsung, these LED navigation devices would allow the users to ask questions about directions and receive real time answers. This AI component will come preprogrammed into the microcontroller in the LED device. Additionally, the sending and receiving of directional data is similar to satellite and GPS devices. The satellite is akin to the LED device that contains the software and sends signals containing location data. And the GPS device, like the ones in many cars, is akin to the small VLC device that the user would carry around.
Thus, utilizing VLC in smart systems provides a method of independent navigation for blind people. The visually impaired deserve dignity, security, and the freedom to move about independently as other people do. In this article we will introduce two different prototypes of VLC enabled indoor navigation systems for the visually impaired that were built in 2017-2018.
VLC Indoor Navigation Prototype I
The first prototype was created by Kulkarni et al. in 2017 . The overall idea is to utilize a smartphone app or small device attached to the user’s walking stick to receive data from LED lights and playback auditory cues to the user. This prototype utilizes all components described in a previous article on Li-Fi. To recap, the transmitter sub-assembly includes LED lights that sends a coded data signal towards the receiver component that decodes the signal into digital data. Specifically, this transmitter also includes a microcontroller, and a user interface. Just as the transmitter, the receiver component uses a microcontroller as well as phototransistors and a display device for the output. Along with that, the receiver utilizes headphones to relay the receiver’s audio cues to the user. Now we will describe in more detail about the architecture of this prototype.
Microcontroller and Optical Communication
When the user asks for directions to a certain destination, the VLC navigation device signals to light fixtures in the ceiling or walls of the building. These light fixtures are the transmitter components of the system. In this prototype, the lights in each hallway, room, etc. automatically send data revealing the location of each place. Additionally, the transmitter contains computer software that calculates the most efficient and easy to walk path towards the user’s selected destination. The device then uses a serial communication interface to relay the data to the processor. Now we get into the optical communication, starting with the processor. It takes the binary data from the computer, and translates the 1’s to “ON” states, and 0’s to the “OFF” states (On-Off Keying modulation). Using an array of white LEDs and an LED driver to transmit the light data, the phototransistor in the receiver side collects the signals.
Following, the receiver’s microcontroller will match up the LED’s ON/OFF states to binary data. Next, the memory which contains stored ASCII values will help the processor convert the bytes to text values. Finally, the text is output to the user’s computer and its software. With the help of a transistor and comparator, the text is converted to speech and audio directions are played into the user’s headphones. In the following sections we will discuss another VLC navigation prototype created by the group Jyothi et al. 2017 .
VLC Indoor Navigation Prototype II
Like the first prototype, the light data in this prototype is processed in essentially the same way. However, the team with Jyothi et al. used a few different components to build the transmitters and receiver devices. First, their transmitter contains a Microcontroller, LED lights, Transformer, Mosfet Driver circuit. On the other side, the receiver is also made up of a Microcontroller, transformer, and a MOSFET driver circuit which includes a photo diode and speaker. In short, the MOSFET driver circuit acts as a power amplifier. What this means is it takes a low power input and gives a large amount of current to high power transistor or MOSFET.
Overall, this prototype functions in a very similar manner to the prototype built by Kulkarni et al. In brief, the photodiodes of the receiver takes in light from the transmitter and uses the processor to calculate directions. Immediately following, the device will let the user know their location and whereabouts through a speaker. Accordingly, the choice of prototype to go forward with is up to the team’s available resources. Thus, both Prototype I by Kulkarni et al. and Prototype II by Jyothi et al. appear to be excellent choices as the components they used are readily available, cheap, and accessible to the public.
In our modern world there are many hazards and complicated building layouts to consider when journeying out on your own. Unfamiliar buildings and other indoor environments are a particular risk for blind people to navigate. VLC systems using LEDs could mitigate these risks and help aid the visually impaired with directions. With VLC indoor navigation systems, we can gain a technology that will help guide us to lead a more secure and efficient life.
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