Table of Contents
Introduction:
Li-Fi, an alternative to Wi-Fi that transmits data using the spectrum of visible light, has achieved a breakthrough, with UK scientists reporting transmission speeds of 10Gbit/s – more than 250 times faster than ‘superfast’ broadband. The fastest speed previously reported was 3Gbit/s, achieved earlier this year by the Fraunhofer Heinrich Hertz Institute in Germany. Chinese researchers also claimed this month to have produced a 150Mbp/s connection, but some experts were doubtful without seeing further proof.
The term Li-Fi was coined by Edinburgh University’s Prof Harald Haas during a TED talk in 2011 (see below for video) though the technology is also known as visible light communications (VLC). Many experts claim that Li-Fi represents the future of mobile internet thanks to its reduced costs and greater efficiency compared to traditional Wi-Fi.
Both Wi-Fi and Li-Fi transmit data over the electromagnetic spectrum, but whereas Wi-Fi utilizes radio waves, Li-Fi uses visible light. This is a distinct advantage in that the visible light is far more plentiful than the radio spectrum (10,000 times more in fact) and can achieve far greater data density. Li-Fi comprises a wide range of frequencies and wavelengths, from the infrared through visible and down to the ultraviolet spectrum. It includes sub-gigabit and gigabit-class communication speeds for short, medium, and long ranges, and unidirectional and bidirectional data transfer using line-of-sight or diffuse links, reflections, and much more. It is not limited to LED or laser technologies or to a particular receiving technique. Li-Fi is a framework for all of these providing new capabilities to current and future services, applications, and end users. This brilliant idea was first showcased by Harald Haas from the University of Edinburgh, UK, in his TED Global talk on VLC. He explained,‖ Very simple, if the LED is on, you transmit digital 1; if it’s off you transmit a 0. The LEDs can be switched on and off very quickly, which gives nice opportunities for transmitting data.
Block diagram explanation:
Power supply unit
This section needs two voltages viz., +12 V & +5 V, as working voltages. Hence specially designed power supply is constructed to get regulated power supplies.
Microphone:
A microphone is an acoustic-to-electric transducer or sensor that converts sound in the air into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, life and recorded audio engineering, two-way radios, megaphones, radio and television broadcasting, and computers for recording voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or knock sensors.
Preamplifier:
A preamplifier (preamp) is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main instrument without significantly degrading the signal-to-noise ratio(SNR)
Power amplifier:
An audio power amplifier is an electronic amplifier that amplifies low-power audio signals (signals composed primarily of frequencies between 20 – 20 000 Hz, the human range of hearing) to a level suitable for driving loudspeakers. It is the final electronic stage in a typical audio playback chain.
Li-Fi transmitter and receiver:
Li-Fi is implemented using white LED light bulbs at the downlink transmitter. These devices are used for illumination only by applying a constant current. By fast and subtle variations of the current, optical output can be made to vary at extremely high speeds. This variation is used to carry high-speed data.
Methodology:
In the process of voice communication through the visible light on the transmitter side voice is used as the input signal. This signal is converted to an electrical signal through a condenser or microphone. This electrical signal is amplified by the amplifier circuits and fed into the power LED. The light signal from the LED varies according to the intensity of the voice signal. The louder the voice the more glow the LED will be. At the receiver side light dependant resister will receive the light signal and correspondingly generate an electrical signal proportional to it. This electrical signal is processed by a demodulator circuit, which is then fed to a speaker and produces the audio signal which was at the input of the transmitter side.
Advantages:
- A free band that does not need a license.
- High installment cost but very low maintenance cost.
- Cheaper than Wi-Fi.
- Theoretical speed up to 1 GB per second: Less time & energy consumption.
- Lower electricity costs.
- Longevity of LED bulb: saves money.
- Light doesn’t penetrate through walls: secured access.
Disadvantages:
- We still need Wi-Fi we still need radio frequency cellular systems. You can’t have a light bulb that provides data to a high-speed moving object or provide data in a remote area where there are trees and walls and obstacles behind.
Applications:
- The remote control devices under the ocean: radio wave doesn’t work there.
- Petrochemical plants: radio wave data transmission is not secured there.
- Hospitals: for medical purposes.
- Street lights, traffic signals: for traffic update.
- Aircraft cabins: for emergency conversations
