A brief introduction to Li-Fi

The articles is intended to give a brief idea about Li-Fi technology

What is LiFi?

The term Li-Fi stands for Light Fidelity. Li-Fi is a wireless communication technology which utilizes light to transmit data between devices. It works based on visible light communication (VLC) principle. Technically, LI-Fi is wireless optical networking based technology which uses LEDs for transmission of data and photodiodes for reception of data

               Official logo of Li-Fi

Visible Light Communication:

Visible light communication (VLC) is a communication technique which uses visible light between 400 terahertz (THz) to 800 THz for transmission of data. VLC is a part of optical wireless communication technology. The technology uses fluorescent lamps or LEDs to transmit signals.

 History of Li-Fi:

Professor Harald Haas is the founder of LI-FI technology. The term Li-FI was first introduced by Harald Haas during a 2011 TEDGlobal talk in Edinburgh. On 20th JULY 2011, he used a table lamp with an LED bulb to transmit a video of blooming flowers that was then projected on to the screen. He periodically blocked the lamp to prove that lamp was indeed the source of incoming data.

 

Light Spectrum Used in Li-Fi:

The spectrum of sunlight consists of different rays such as gamma rays, UV rays, visible light, X-rays, infrared rays etc. The UV rays, gamma rays are dangerous to human body. Exposure to infrared rays for a considerable period may damage the vision. So, keeping in mind of safety of individuals, only visible light is being used in Li-Fi.

 

Working Principle:

Li-Fi works by switching the current to the LEDs on and off at very high speed which is very quick for a human eye to notice the flickering. It uses light from LEDs as a medium to deliver network, mobile, highspeed communication similar to WI-FI (Wireless Fidelity). It transmits digit 1 when the LED is ON and digit 0 when the LED is OFF. The LEDs can be dimmed to below human visibility while still emitted light can carry the data

Construction of LI-FI:

Factors to be considered to design a Li-Fi system are as follows:

1) Presence of Light

2) Line of Sight (Los)

3) for better performance use fluorescent light LED

The above figure shows simple construction on a LI-Fi network. The server is provided with a Li-Fi transmitter and the client is provided with receiver. The transmitter consists of a voltage regulator, level shifter and transmitter circuit connected to a LED. The receiver consists of a photodiode connected to receiver circuit with a level shifter.

Block Diagram:

The above picture explains how Li-Fi can help us communicate data. In Li-Fi, the LED lamp acts as a transmitter and photodetector acts as a receiver. The data from the internet is transmitted to the LEDs through lamp driver. The lamp driver controls the power supply to the LEDs. When the data bit 0 needs to be transmitted, the LED will be OFF and when data bit 1 needs to be transmitted, the LED will be ON. The Li-Fi dongle is the Li-Fi receiver. It contains photo detector to detect the light. Whenever it detects the LED off bit 0 will be taken as output and 1 will be taken as output when LED is ON. The signal from photo detector is then passed through amplification and processing stage. After processing the information, the information is transferred to the receiver device (a laptop or PC or a mobile).

                                          LIFI communication

 

Specifications:

The PHY (physical) and MAC (media access control) layers of LIFI are defined in IEEE 802.15.7 standard. LI-Fi Can transmit audio, video and multimedia services using this standard. The MAC layer permits using Link with other layers as with TCP/IP protocol.

IEEE 802.15.7 defines 3 PHY layers with different rates. They are:

  1. PHY 1: This layer was established for outdoor application and works from 11.67 kilobits per second(kbit/s) to 267.6 kbit/s.
  2. PHY 2: This layer permits reaching data rates from 1.25 Megabits per second (Mbit/s)to 96 Mbit/s.
  3. PHY 3: This layer is used for many emissions sources with a particular modulation technique called color shift keying (CSK). PHY 3 can deliver data rate from 12Mbit/s to 96Mbit/s.

Modulation techniques recognized for PHY1 PHY2 are on-off keying (OOK) and variable pulse position modulation (VPPM). The Manchester coding used for PHY1 and PHY2 layers includes the clock inside the transmitted data it represents logic 0 with “01” and logic 1 with “10”, all with a DC component. The DC component helps to avoid light extinction when there is an extended run of logic 0’s. 

The IEEE 802.15.7 standard is out of date as it fails to consider the latest developments in the field of optical wireless communications, specifically with introduction of optical orthogonal frequency division multiplexing(O-OFDM) modulation methods which have been optimized for data rates, multiple access and energy efficiency. The introduction of O-OFDM creates the need for development of a new drive for standardization of optical wireless communications. Researches reached a data rate of 224Gbit/s using Li-Fi.

Li-Fi vs Wi-Fi:

Both Li-Fi and Wi-Fi provides wireless internet access, and both the technologies transmit data using electromagnetic spectrum. Li-Fi is a visible light communication technology which obtains high speed wireless communication. The major difference between the two is Wi-Fi uses radio waves for transmission, whereas Li-Fi utilizes light waves specifically visible light. Wi-Fi is suitable for general wireless coverage within buildings or institutional campus or compound, and Li-Fi is best suited for high density wireless data coverage inside a room or a confined area and is free from interference issues.

The above table gives an idea about the differences between Wi-Fi and Li-Fi.

The above table gives the idea about data speed of different wireless communication technologies.

Drawbacks of Wi-Fi in comparison to Li-Fi:

 

  1. a) Bandwidth: Wireless data is transmitted through radio waves which are limited and expensive. It has a limited bandwidth, when compared to Li-Fi. With the rapidly increase in usage of Wi-Fi, 4G and 5G technologies, the band width of RF waves available is being reduced.
  2. b) Power Consumption: There are a large number of cellular radio base stations that consume massive amount of energy. Power dissipated by base station is more than the power used for of transmission. Thus, efficiency of the radio base stations is very less.
  3. c) Availability: Availability of radio waves is also a concern as the bandwidth is reserved for certain fields.
  4. d) Security: Radio waves can penetrate through walls. They can be hacked from a remote location. This causes a major security concern for Wi-Fi.
  5. e) Usage in RF areas: Radio waves are not advisable to be used in aerial vehicles and at places where radio interference may cause

undesirable/catastrophic result.

 

Advantages of LI-FI:

Li-Fi, which uses visible light to transmit signals wirelessly, is an emerging technology which has ability to compete with Wi-Fi. Also, Li-Fi helps the user to overcome the limitations of Radio wave transmission such as Wi-Fi. Advantages of Li-Fi technology include:

  1. a) Efficiency: Energy consumption is reduced with the use of LED illumination

which are already available in the society for lighting purpose. Hence, the transmission of data requires negligible additional power, which makes it very efficient in terms of costs and energy.

  1. b) High speed: Combination of low interference, high bandwidths and high-intensity output, help Li-Fi provide high data rates i.e. 1 Gbps or even beyond.
  2. c) Availability: Availability is not an issue as light sources are present everywhere. Wherever there is a light source, there can be Internet. Light bulbs are present everywhere - in homes, offices, shops, malls and even planes, which can be used as a medium for the data transmission.
  3. d) Economic: Li-Fi not only requires fewer components for its working, but also uses only a negligible additional power for the data transmission.
  4. e) Security: Li-Fi provides enhanced security. Since light penetrate through walls, Li-Fi internet is available only to the users within a confined area and cannot be intercepted and misused, outside the area under operation.
  5. f) Li-Fi technology has a great scope in the near future. The extensive growth in the usage of LEDs instead of fluorescent lights for illumination indeed provides the opportunity to integrate the technology into a plethora of environments and applications.

 

Limitations of Li-Fi:

The major limitations of Li-Fi are:

  1. a) Internet cannot be accessed without a light source. This limits the locations and situations in which Li-Fi could be used.
  2. b) It requires a near or perfect line-of-sight mode to transmit data.
  3. c) Opaque objects in transmission can affect data transmission.
  4. d) Sunlight and electric light can affect the data transmission speed and also interfere with the signal.
  5. e) Light waves don’t penetrate through walls and so Li-Fi has a much shorter range than Wi-Fi.
  6. f) High installation cost.

 

Applications:

Li-Fi has a wide area of applications. Few of them are:

a) Aviation: Effective communication of data in airborne environments such as aeroplanes utilizing Li-Fi. By using light-based transmission technique it will not interfere with equipment working on radio waves such as RADAR.

b) Hospital: Li-Fi could be a better system to transmit communication about patient’s information. Besides providing a higher speed, Light waves have little interference on medical instruments

c)Vehicles: Vehicles with Li-Fi could communicate with front and back lights. Street lights and traffic signals can provide info about current situation. Thus it helps in vehicle automation.

d) Underwater Application: Li-Fi could be used in remotely operated underwater vehicles (ROVs) which are mostly controlled by wired connections. Thus, it can offer high mobility by replacing wired cables for communication. Significant amount of light do not penetrate further than 200 meters. No light can penetrate more than 1000 meters

Industrial and Home Automation: As Li-Fi signals cannot penetrate through walls, the system becomes more secure as it is impossible to hack from remote location. Also, Li-Fi speed is almost real time which is desirable for automation.

Advertising: Street lamps can be used to display advertisements and in retail stores, front lights can show current offers on customer’s cellular device.

Future Scope:

Li-Fi bandwidth is of free bandwidth so most of the people will use Li-Fi in the near future. Once the researchers develop the system reliably it has the potential to replace Wi-Fi in almost all areas. It can convert every bulb into a data transmission unit. Due to the high speed of Li-Fi people may prefer more.  Currently, Broadcast solution or LBS (location Based Service) are commercially available. The next step could be a Li-Fi WLAN.

 

Conclusion:

Still there is a long way to make this technology a commercial success but it assures

a great potential in the field of wireless internet. Many researchers and companies are currently working on this concept thus it assures that we can solve the problems of low bandwidth, low speed and low security. It helps to reduce adverse effects of radiation caused and radio waves. Li-Fi is the upcoming and growing technology which is attracting researchers to develop new inventions/technologies. Therefore, there is certainty of development of future applications of the Li-Fi which can be extended to different fields.

 

 

 

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