Visible Light Communication-History, Working & Applications

Charles John April 4, 2018 No Comments

Over the few past years, a myriad of technological advancements has been evidenced in the lighting and communication sector. The most amusing one being visible light communication (VLC). Invented in the late in the 18th century, the means has not only undergone numerous advancements but also applied in different sectors.

What is Visible Light Communication aka VLC?

Visible Light Communication is a communication method where visible light within a particular frequency range is used as the medium of communication. The visible light frequency range for VLC is from 400 to 800 THz.

VLC operates under the concept of transmission of data via light rays to send and receive messages in a given distance. Putting to use LED lighting, VLC can be used as a replacement for radio frequencies in areas it cannot be applied. In addition, VLC has the upper hand over radio frequencies as it offers ultra-fast data transmission and also high bandwidth transmission. This has been most evident in traffic lighting, besides other sectors.

Being a complex field, it arouses questions on its significance, its operation, and areas in which it is well suited for.

History of Visible Light Communication

The concept of VLC (visible light communication) dates back as early as 1880 (4 years prior to the invention of radio transmission). This was first put into use by alexander graham bell, a Washington D.C resident when he invented the photophone. The method relayed speech over long distances via modulated sunlight. However, back then the idea was not applied much as it was centuries ahead of its time. Due to this, the technology paved way for slower communication media thus was never a big hit. However, this acted as a guiding line for fiber optic communication that was invented in the 80’s. later in 1995, students of Universidad de Buenos Aires worked on the concept and thus resulted in a laser diode that was used in photodiodes detection. in 2003, three undergraduates from Keio University, Japan, worked more on the concept using LED lighting.

Given the presence of sophisticated technology, people were able to manipulate the technology and put it to use. In 2006, CICTR researchers combined LED lighting to power line communication and resulted in a number of indoor applications of VLC. Over the years, the technology underwent a number of researchers and changes and thus leading to various uses inclusive of High definition videos. This technology found its way into the security field, transport sector and even banking sectors between 2010 and 2017.

Working – How Visible Light Communication Works?

Given that light travels 186,000 miles in a second, communication via this source is virtually instantaneous. This makes VLC the fastest means of communication between all means available in the market. to function, VLC uses visible light between 780 to 375 nm which are visible to the human eye. Every form of data can be broken down into single units of ones and zeroes that can be deciphered as low or high signals. In VLC, this is achieved by fast turning of light on and off (also called on-off keying, OOK). However, this form of data transmission is dependent on how fast the light can go on and off. To achieve great results, LED lighting is well suited for the task as it has a short rise and fall time thus faster switching. Due to this, LED lighting is used in all wireless forms of VLC.

To function, VLC requires a receiver (photodetector), a transmitter (LED’s) and a channel of communication. In addition, the circuit features a photodiode, transimpedance amplifiers, auto gain controllers, high pass filters and in some cases analog-digital converters. From the source of the signal, an enhanced photodiode is fitted so as to convert light into a current. At the source and recipient of the instructions, a digital unit is fitted so as to encode and decode the instructions relayed accordingly. So as to increase the speed and the gain of the photodiode, a transimpedance amplifier is used to make the process faster. Additionally, an automatic gain control is featured thus boosting speeds for messages between the sender and the receiver.

Once the message is relayed, the photodiode on the other end breaks the current into a voltage that can be interpreted by the computer as a unit of ones and zeros hence achieving a targeted result. So as to prevent disturbance from surrounding light sources, a high pass filter is used in the model. However, this is a passive set of both the transimpedance amplifier and the auto gain controllers are both gainers and no more gain was required. With this, the set is completed and thus messages are delivered instantly without external disturbances.

With the circuit complete, various software are required for the system to operate. This consists of parts like; data packaging, hardware control, encoding and decoding, error handling and synchronization. With the appliance of Linux network module, VLC technology can be used with any application that runs on a Linux computer. Since the set works with encoding and decoding of data, appropriate software is needed so as to complete it. This will handle packages in the system and ensure that each command is performed appropriately. The transmitter sends a preamble that is synchronized with the receiver and thus data is transmitted followed by a checksum. Once data is submitted, the command is applied or transmitter waits for a message. Once the receiver gets the message relayed, a signal is sent to the transmitter by applying the command. So as to handle any errors that may arise in the process, checksums are sent alongside data. If the sender’s checksum is identical to the one with a receiver, the message will be relayed thus enabling transmission of the next package.

The procedure is carried out repeatedly until packets are successfully relayed and intended purpose is achieved.

Applications of VLC

Being the fastest means of relaying messages, VLC has been put to use in a number of fields. However, wired VLC is used in more instances as wireless VLC is limited to open spaces and cannot pass through fields that have obstructions like walls. This limits wireless VLC to indoor applications and few outdoor functions provided that no barrier exists between the sender of the message and the recipient.

Among the uses of VLC are;

Smart lighting:

With the infusion of technology with real estate development, smart homes have become a trendy topic. With VLC in housing, one will be able to connect to fast speeds of data transmission in the house and also have a cheaper source of bright light. With appliance of VLC in a building, one will not only cut on the cost of wires but also save the electricity costs

Infrastructure and transportation:

Among the fields that highly apply visible light communication, the transport sector is on top of the list. Ranging from traffic signs, street lamps, and car LED’s VLC proves to be a great addition. Not only because the minimal wiring is required but also because the systems get to operate efficiently with minimal chances of damage. In vehicle indicators, VLC is used to send signals to the LED lights thus achieving communication between vehicles. The messages indicated via this medium include breaking warning, direction indicators, and hazard lighting. This, in turn, prevents road accidents and carnages.

Security purposes:

Unlike other media transmission of data, chances of messages being relayed via VLC getting intercepted are equally low. This given that one across the wall cannot access the messages getting delivered on the other side of the wall. This, in turn, reduces the ability of messages leaking as the messages will be accessed by people within a given floor space. Additionally, this method is way faster than other methods present and thus few instances of delay of messages.

Mobile connectivity:

By directing a visible light to another device, a high-speed medium of data transmission is created. This medium is way faster than Bluetooth and equivalent transmission methods hence ability to transfer large data packets within a small duration of time.

Healthcare sector:

In hospitals, several machines will benefit from VLC as they will get less interference from radio waves from other machines. This will reduce interruption from other devices using radio waves hence easier operation.

Li-fi- unlike Wi-Fi where a radiofrequency is used, Li-Fi solely depends on the light so as to operate. With this, data is relayed faster and costs on wiring are saved.

Aviation:

Since radiofrequency is warned against by several flights in passenger compartments, VLC would be a great replacement. This provided that LED lighting already exists in aircraft. Usage of VLC will reduce the overall weight of the plane and cut on wiring costs. Additionally, passengers will enjoy fast data connections hence easy communication inflight.

Conclusion

Many years back when graham bell introduced virtual light communication, it did not hit as much. However, Bell said that this was going to be a great invention in the future and indeed it is. Featuring fast transmission speeds and high bandwidth with few interferences from other media, VLC shows a promising future. With the improvement of technology to sophisticated levels, VLC has proved to be a fruitful endeavour as it aids in numerous appliances. This ranging from the medical field to the transport sector. This shows that with more manipulation in the future, there is more VLC has to offer than it has now.

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