ECO-FRIENDLY DATA TRANSMISSION THROUGH LI-FI · PDF fileInternational Conference on Current...

International Conference on Current Research in Engineering Science and Technology (ICCREST-2016)

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ECO-FRIENDLY DATA TRANSMISSION THROUGH LI-FI TECHNOLOGY

K. Stella1, R. Sivaranjani2, G. Nagasundari3. 1PG student, Department of ECE, Vivekanandha College of Engineering for Women 2PG student, Department of ECE, Vivekanandha College of Engineering for Women 3PG student, Department of ECE, Vivekanandha College of Engineering for Women

Abstract: In recent era, most of the people are using internet to achieve their task through wired or wireless network. As number of users get inflate in wireless network speed deflate proportionally. As per IEEE 802.11.n the Wi-Fi provides speed up to 150mbps, although practically very less speed is received. To overcome this limitation, we are introducing the concept of Li-Fi. The Light Fidelity is a bidirectional, high speed and fully networked wireless communication similar to Wi-Fi. Li-Fi is a form of Visible Light Communication (VLC). VLC uses rapid pulses of light to transmit information that cannot be detected by the human eye. Further enhancements can be made in this method, like using an array of LEDs for parallel data transmission, or using mixtures of red, green and blue LEDs to alter the light’s frequency with each frequency encoding a different data Channel. Such advancements promise a theoretical speed of 10 Gbps – meaning one can download a full high-definition film in just 30 seconds. Keywords: Li-Fi, LED, Wi-Fi, visible light, data transmission.

I INTRODUCTION.

Over the past few years there has been a rapid growth in the utilization of the RF region of the electromagnetic spectrum. This is because of the huge growth in the number of mobile phones subscriptions in recent times. This has been causing a rapid reduction in free spectrum for future devices. Light-fidelity (Li-Fi) operates in the visible light spectrum of the electromagnetic spectrum i.e. it uses visible light as a medium of transmission rather than the traditional radio waves.

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 works 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. [1].

Li-Fi can play a major role in relieving the heavy loads which the current wireless systems face since it adds a new and unutilized bandwidth of visible light to the currently available radio waves for data transfer. Thus it offers much larger frequency band (300 THz) compared to that available in RF communications (300GHz). Also, more data coming through the visible spectrum could help alleviate concerns that the electromagnetic waves that come with Wi-Fi could adversely affect our health. Li-Fi can be the technology for the future where data for laptops, smart phones, and tablets will be transmitted through the light in a room. Security would not be an issue because if you can‘t see the light, you can‘t access the data. As a result, it can be used in high security military areas where RF Communication is prone to eavesdropping.

II CONSTRUCTION OF LI-FI SYSTEM

Li-Fi is a fast and cheap optical version of Wi-Fi. It is based on Visible Light Communication (VLC).VLC is a data communication medium, which uses visible light between 400 THz (780 nm) and 800 THz (375 nm) as optical carrier for data transmission and illumination. It uses fast pulses of light to transmit information wirelessly. The main components of Li-Fi system are as follows: a) a high brightness white LED which acts as transmission source. b) a silicon photodiode with good response to visible light as the receiving element.

LEDs can be switched on and off to generate digital strings of different combination of 1s and 0s. To generate a new data stream, data can be encoded in the light by varying the flickering rate of the LED. The LEDs can be used as a sender or source, by modulating the LED light with the data signal. The LED output appears constant to


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the human eye by virtue of the fast flickering rate of the LED. Communication rate greater than 100 Mbps is possible by using high speed LEDs with the help of various multiplexing techniques. VLC data rate can be increased by parallel data transmission using an array of LEDs where each LED transmits a different data stream. The Li-Fi emitter system consists of 4 primary subassemblies[3]: a) Bulb b) RF power amplifier circuit (PA) c) Printed circuit board (PCB) d) Enclosure

The PCB controls the electrical inputs and outputs of the lamp and houses the microcontroller used to manage different lamp functions. A RF (radio-frequency) signal is generated by the solid-state PA and is guided into an electric field about the bulb. The high concentration of energy in the electric field vaporizes the contents of the bulb to a plasma state at the bulb‘s center; this controlled plasma generates an intense source of light. All of these subassemblies (shown in Fig. 1) are contained in an aluminum enclosure [3].

Fig. 1. Block diagram of Li-Fi sub-assemblies

The bulb sub-assembly is the heart of the Li-Fi emitter. It consists of a sealed bulb which is embedded in a dielectric material. This design is more reliable than conventional light sources that insert degradable electrodes into the bulb [5]. The dielectric material serves two purposes. It acts as a waveguide for the RF energy transmitted by the PA. It also acts as an electric field concentrator that focuses energy in the bulb. The energy from the electric field rapidly heats the material in the bulb to a plasma state that emits light of high intensity and full spectrum [3]. Figure 2 shows the bulb sub-assembly.

Fig. 2. Bulb sub-assembly [10]

There are various inherent advantages of this approach which includes high brightness, excellent color quality and high luminous efficacy of the emitter – in the range of 150 lumens per watt or greater. The structure is mechanically robust without typical degradation and failure mechanisms associated with tungsten electrodes and glass to metal seals, resulting in useful lamp life of 30,000+ hours. In addition, the unique combination of high temperature plasma and digitally controlled solid state electronics results in an economically produced family of lamps scalable in packages from 3,000 to over 100,000 lumens [4].

III WORKING OF LI-FI Li-Fi is typically implemented using white LED

light bulbs at the downlink transmitter. These devices are normally used for illumination only by applying a constant current. However, by fast and subtle variations of the current, the optical output can be made to vary at extremely high speeds. This very property of optical current is used in Li-Fi setup. The operational procedure is very simple if the LED is on, you transmit a 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. Hence all that is required is some LEDs and a controller that code data into those LEDs. All one has to do is to vary the rate at which the LED’s flicker depending upon the data we want to encode. Further enhancements can be made in this method, like using an array of LEDs for parallel data transmission, or using mixtures of red, green and blue LEDs to alter the light’s frequency with each frequency encoding a different data channel. Such advancements promise a theoretical speed of 10Gbps – meaning one can download a full high-definition film in just 30 seconds. [12].



Fig:3 Implementation of Li-Fi

If the LED is on, you transmit 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.” So what you require at all are some LEDs and a controller that code data into those LEDs. We have to just vary the rate at which the LED’s flicker depending upon the data we want to encode. Further enhancements can be made in this method, like using an array of LEDs for parallel data transmission, or using mixtures of red, green and blue LEDs to alter the light’s frequency with each frequency encoding a different data channel. Such advancements promise a theoretical speed of 10 Gbps –meaning you can download a full high-definition film in just 30 seconds. Simply awesome! But blazingly fast data rates and depleting bandwidths worldwide are not the only reasons that give this technology an upper hand. Since Li-Fi uses just the light, it can be used safely in aircrafts and hospitals that are prone to interference from radio waves. This can even work underwater where Wi-Fi fails completely, thereby throwing open endless opportunities for military operations. Imagine only needing to hover under a street lamp to get public internet access, or downloading a movie from the lamp on your desk. There's a new technology on the block which could, quite literally as well as metaphorically, throw light on how to meet the ever-increasing demand for high-speed wireless connectivity. Radio waves are replaced by light waves in a new method of data transmission which is being called Li-Fi. Light-emitting diodes can be switched on and off faster than the human eye can detect, causing the light source to appear to be on continuously. A flickering light can be incredibly annoying, but has turned out to have its upside, being precisely what makes it possible to use light for wireless data transmission.

Fig:4 Data transmission using LED

Light-emitting diodes (commonly referred to as LEDs and found in traffic and street lights, car brake lights, remote control units and countless other applications) can be switched on and off faster than the human eye can detect, causing the light source to appear to be on continuously, even though it is in fact 'flickering'. This invisible on-off activity enables a kind of data transmission using binary codes: switching on an LED is a logical '1', switching it off is a logical '0'. Information can therefore been coded in the light by varying the rate at which the LEDs flicker on and off to give different strings of 1s and 0s. This method of using rapid pulses of light to transmit information wirelessly is technically referred to as Visible Light Communication (VLC), though it’s potential to compete with conventional Wi-Fi has inspired the popular characterization Li-Fi.

IV TECHNICAL ASPECTS

LED as light source The most important requirement for a light

source in order to serve communication purposes is the ability to be switched on and off repeatedly in very short intervals of time. Due to their ability to be switched on and off rapidly, LEDs are suitable light sources for Li-Fi. LEDs offer many benefits over fluorescent lamps and incandescent lamps such as higher efficiency, environment friendly manufacturing, flexibility of design, longer useful lifetimes and improved spectrum performance.

LEDs emit light when the energy levels change in the semiconductor diode. This change in energy generates photons, some of which are emitted as light. The wavelength of emitted light depends upon the difference in energy levels and the type of semiconductor material used to form the LED chip. Solid-state design allows LEDs to



withstand vibration, shocks, frequent switching and extremes of environment without compromising their long useful lives of typically more than 100,000 hours.

Fig 5:LED

The basic LED consists of a semiconductor diode

chip mounted in the reflector cup of a lead frame that is connected to electrical (wire bond) wires, and then encased in a solid epoxy lens. The variations in data rate with the size of LEDs are very important in Li-Fi technology[10]. Different data rates can be achieved with different sized LEDs. Normal sized LED bulbs can be reduced to micro-LEDs which handle millions of variations in light intensity. A micro-LED light bulb can transmit 3.5 Gbps and data rates of more than 10 Gbps are possible. The micro LED bulbs allow the light stream to be beamed in parallel thereby transmitting huge amounts of data in terms of Gbps[6].

V MODULATION SCHEMES

1. On-Off Keying (OOK): The 802.15.7 standard uses Manchester coding so that the period of positive pulses is same as the period of negative ones, however this doubles the bandwidth required for transmission. For higher bit rates, run length limited (RLL) coding is used which is spectrally more efficient. Dimming is supported by adding an OOK extension which adjusts the aggregate output to the correct level.

2. Variable Pulse Position Modulation (VPPM): PPM encodes the data using the position of the pulse within a set time period .The duration of the period containing the pulse must be long enough to allow different positions to be

identified. VPPM is similar to PPM but it allows the pulse width to be controlled to support light dimming[11].

3. Colour Shift Keying (CSK): This is used if the illumination system uses RGB-type LEDs. By combining different colours of light, the output data can be carried by the colour itself and hence the intensity of the output can be near constant. Mixing of RGB primary sources produces different colours which are coded as information bits[7]. The disadvantage is that it increases the complexity of the transceivers.

4. Sub-Carrier Inverse PPM (SCIPPM): This method is divided into two parts (1) sub-carrier part and (2) DC part. The DC part is used only for lighting or indicating. When there is no requirement for lighting or indicating, SCPPM (Sub-Carrier PPM) is used in order to save energy.

5. Frequency Shift Keying (FSK): In this method, data is represented by varying the frequencies of the carrier signal. Before transmitting two distinct values (0 and 1), there needs to be two distinct frequencies.

6. SIM-OFDM (Sub-Carrier Index Modulation OFDM): This is a new approach to transmission in which an additional dimension is added to conventional 2D amplitude/phase modulation (APM) techniques such as quadrature amplitude modulation (QAM) and amplitude shift keying.

Multiple Access A seamless all-optical wireless network would

require ubiquitous coverage provided by the optical front-end elements. This necessitates the usage of a large amount of Li-Fi enabled lighting units. The most likely candidates for front-end devices in VLC are incoherent solid-state lighting LEDs due to their low cost. Due to the physical properties of these components, information can only be encoded in the intensity of the emitted light, while the actual phase and amplitude of the light wave cannot be modulated. This significantly differentiates VLC from RF communications[9]. A networking solution cannot be realized without a suitable multiple access scheme that allows multiple users to share the communication resources without any mutual cross-talk.

Multiple access schemes used in RF communications can be adapted for OWC as long as the necessary modifications related to the IM/DD nature of the modulation signals are performed. OFDM comes with a natural extension for multiple accesses – OFDMA.

Single-carrier modulation schemes such as M-PAM, OOK and PWM require an additional multiple access technique such as frequency division multiple access (FDMA), time division multiple access (TDMA) and/or code division multiple access (CDMA)[8]. The results of



an investigation regarding the performance of OFDMA versus TDMA and CDMA are presented in Fig. 3.18 FDMA has not been considered due to its close similarity to OFDMA, and the fact that OWC does not use super heterodyning. In addition, due to the limited modulation band width of the front-end elements, this scheme would not present a very efficient use of the LED modulation band width.

Fig:6 Multiple Accesses

VI ADVANTAGES OF LI-FI

Li-Fi technology is based upon lights might be any sort of lights. The transfer of data takes place in presence of any kinds of light whatever may be the band width. Due to which the depend of transmitting the data or information will be great and also sufficient information, music, movies, games anything can be downloaded using very less time. 1. Capacity: Light itself has 10000 times wider bandwidth than radio waves. Due to which the transfer of data is more effectively possible. So Li-Fi has better capacity. 2. Efficiency: LED lights consume less energy and very efficient. As it uses less energy it is cheap and easy to use. 3. Availability: As light is present everywhere, Life is available everywhere. But for more efficient use of Li-Fi technology LED bulbs must be placed for proper transmission on data for proper transmission on data. 4. Security: Light waves cannot penetrate through walls. So they cannot be misused. 5. Bandwidth: The visible light is unlicensed and free to use and gives a very large bandwidth.

6. Data Density: Li-Fi can achieve about 1000 times the data density of Wi-Fi because visible light can be well contained in the tight illumination area. 7. Low Cost: As it requires very few components the cost of it is comparatively low.

VII LIMITATIONS OF LI-FI

1. As Li-Fi technology uses light as transmission medium, so if the receiver is somehow blocked in a way then the signal will immediately will be cut out. 2. While data transfer interference from external light sources such as sunlight, normal bulbs, and opaque materials can cause loss of reliability and network. 3. As Li-Fi works in direct line of slight. Slight disturbance can cause to interruption.

VIII APPLICATION OF LI-FI

You Might Just Live Longer For a long time, medical technology has lagged

behind the rest of the wireless world. Operating rooms do not allow Wi-Fi over radiation concerns, and there is also that whole lack of dedicated spectrum. While Wi-Fi is in place in many hospitals, interference from cell phones and computers can block signals from monitoring equipment. Li-Fi solves both problems: lights are not only allowed in operating rooms, but tend to be the most glaring (pun intended) fixtures in the room.

Smarter Power Plants

Wi-Fi and many other radiation types are bad for sensitive areas. Like those surrounding power plants. But power plants need fast, inter-connected data systems to monitor things like demand, grid integrity and (in nuclear plants) core temperature. The savings from proper monitoring at a single power plant can add up to hundreds of thousands of dollars. Li-Fi could offer safe, abundant connectivity for all areas of these sensitive locations. Not only would this save money related to currently



implemented solutions, but the draw on a power plant’s own reserves could be lessened if they haven’t yet converted to LED lighting.

Airlines

Airline Wi-Fi. Nothing says captive audience like having to pay for the "service" of dial-up speed Wi-Fi on the plane. And don’t get me started on the pricing. The best I’ve heard so far is that passengers will "soon" be offered a "high-speed like" connection on some airlines. United is planning on speeds as high as 9.8 Mbps per plane. I have twice that capacity in my living room. And at the same price as checking a bag, I expect it. Li-Fi could easily introduce that sort of speed to each seat's reading light.

Medical and Healthcare

Due to concerns over radiation, operating rooms do not allow Wi-Fi and even though Wi-Fi is in place in several hospitals, interferences from computers and cell phones can block signals from medical and monitoring equipment. Li-Fi solves these problems. Lights are an essential part of operating rooms and Li-Fi can thus be used

for modern medical instruments. Moreover, no electromagnetic interference is emitted by Li-Fi and thus it does not interfere with any medical instruments such as MRI scanners.

Underwater Explorations and Communications

Remotely operated underwater vehicles or ROVs work well except in situations when the tether is not long enough to fully explore an underwater area or when they get stuck. If instead of the wires, light were used then the ROVs would be freer to explore. With Li-Fi, the headlamps could also then be used to communicate with each other, data processing and reporting findings back to the surface at regular intervals, while also receiving the next batch of instructions. Radio waves cannot be used in water due to strong signal absorption. Acoustic waves have low bandwidth and disrupt marine life. Li-Fi offers a solution for conducting short-range underwater communications.

Traffic

Li-Fi can be used for communications between the LED lights of cars to reduce and prevent traffic accidents. LED headlights and tail-lights are being implemented for different cars. Traffic signals, signs and street lamps are all also transitioning to LED. With these LED lights in place, Li-Fi can be used for effective vehicle-to-vehicle as well as vehicle-to-signal communications. This would of course lead to increased traffic management and safety.

IX CONCLUSION

With the growing technology and increasing use of the internet services, possibilities are very high that use of Li-Fi technology will be soon in practice. Every bulb will be replaced by Li-Fi bulbs and might be used like a Wi-Fi hotspot for the transmission of data. Using Li-Fi technology will grant a cleaner, greener and brighter future and environment. The concept of Li-Fi is spreading so fast as it is easy to use, it is attracting interest of people. The use of Li-Fi technology gives a very golden opportunity to replace or to give alternative to the radio based wireless technologies. As the number of people and the access of internet is increasing on such a large scale , accessing internet through Wi-Fi will soon be insufficient as the usage is increasing but the bandwidth remains the same. As network traffic will increase it will result in lowering the speed of accessing the internet thus more increasing prices. The airways become clogged making it more difficult to use. Thus the use of Li-Fi will increase the speed of data transfer and also it is accessible in many banned places thus it will be availsable for all.



REFERENCES

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