The Similarities and Differences between Li-Fi And Wi-Fi

Abstract

As we grow as a society, the methods of which we use to access the internet in our everyday lives will continue to grow as well. This case study will try to come to a conclusion on which method is the most practical for society, in this particular case the new upcoming technology known as Li-Fi VS the most popular used wireless technology known as Wi-Fi. This paper will also dive into the architecture, applications of Li-Fi in everyday scenarios Li-Fi and Wi-Fi hybrid networks. In this paper, further information on the practicality of Li-Fi is gained through the simulation results and the explanation of these results.

Introduction

As the world of wireless communication continues to evolve, there is a rising demand for wireless data communication. Due to this rising demand, wireless communications schemes such as Wi-Fi may not be able to support the growth of the Internet of Things (IoT). This is due to the fact that Wi-Fi uses radio/micro wave frequencies for data transmission as we know inherently the radio/micro wave frequency can only support a finite amount of bandwidth. According to an article written by Kara Lant for online Futurism blog by 2020 there will be a total of four devices connected to the internet per human, that is a staggering number of 24 billion devices connected to the internet. The wireless communication industry has responded predicament by suggesting that we look at utilizing the radio spectrum above 10GHz. But there is a major problem, as Frequency increases f according to Friss free space equation, L path loss will increase as L  f2. To add to this, blockage such as walls or any other obstructions are harder to overcome at higher frequencies. This is when of Li-Fi comes into play, the idea of Li-Fi is ‘Data transmission through illumination’. To give some background of Li-Fi, Professor Harald Haas a German Professor of Mobile Communications at the University of Edinburgh popularized the term 'Li-Fi' (which stands for Light Fidelity) at his 2011 TED Global Talk. At this talk he introduced the idea of 'wireless data from every light”. The general term 'visible light communication' (VLC). To link an earlier point made in this paper, the IoT is growing at an exponential rate and Li-Fi could be the network solution for multiple user accesses. Through Li-Fi illumination of a desk lamp and the connectivity of a laptop to internet can be proved simultaneously. According to an article written by www.alphr.com ,It is said to have data transfer speeds well over 3 Gb/s, this is 100 times faster than the speed of normal Wi-Fi. In section 2 the main differences between Wi-Fi and Li-Fi will be dived into, in section 3 the architecture of Li-Fi and how it works will be explained. Section 4 will give an idea of how a hybrid network system of Li-Fi and Wi-Fi would work. Section 5 will give practical examples of how Li-FI would work in real life environments. Section 6 explains the simulation scenario and the discussion of these results and finally with section 8 a conclusion will be made about the advancement of Li-Fi and its place in the wireless technology industry.

Li-Fi vs Wi-Fi what are the simulations what the differences are?

Wi-Fi uses radio/micro wave frequencies to transmit data. In the case of Li-Fi it uses LEDs as visible Light Transmitters. When these LEDs are provided with a constant current, a stream of photons are emitted, these photons transmit the data required but it is seen as illumination. This illumination can be modulated at very high speeds, this illumination is then picked up by the photo-detector. By the LEDs performing this action it allows for high speed data transmission from a light bulb to mobile device, a laptop or anything device that has wireless connectivity functions. With Li-Fi the spectrum can be utilised more than 1000 times greater than the spectrum utilised for radio frequencies. It is unlocking unprecedented data and bandwidth [3]. Since Li-Fi uses light for data transmission less interference is likely to occur, when compared to Wi-Fi, this makes is easier for Li-Fi to be used in denser environments which is not always the case with Wi-Fi. When it comes to range, Li-FI and Wi-Fi have a significant difference in range, Li-Fi can only over around about 10, compared to Wi-Fi which is about 32 meters this can vary on antenna type and transmission power. There are both disadvantages and advantages for this limiting range, such as privacy since the Light is blocked by walls data transfer is more secure, whereas as Wi-Fi radio frequencies will penetrate through walls, so techniques need to be employed to achieve a more secure data transmission.

Li-Fi Architecture

Light bulbs are essential in our everyday lives we use them in our rooms, street lights and a number of different environments. To take full advantage of this everyday necessity Li-Fi was born. This means that Li-Fi is based on visual light communication. Visual light communication needs a server, a connection to the internet, light source, photo detector, power lamp driver, an LED bulb and a desktop, these are all the components shown in figure 1 below. The LED bulb acts as the heart of the Li-Fi technology, it preserves a massive portion of electricity by transmitting data and receiving data through the LED bulb or any other type of equipment that emits light. A receiver and a transmitter is fitted on the light emitting diode, a current is also flowing through the LED at very high speeds. Binary coding (or digital coding) is used for sending and receiving data. Data is then transmitted by the LED in the form of 1s and 0s. If the LED is on you send a digital 1, if the LED is off you send a digital 0. This process is done at very quickly so the data can be received at a faster rate.

Li-Fi and Wi-Fi hybrid system

Instead of using Li-Fi by itself or Wi-Fi by itself, why couldn’t we combine the two technologies to complement each other? How would this hybrid system work? A hybrid system of Li-Fi and Wi-Fi would consist of a bi-directional transceiver that would provide communication for the links connected to both. A central unit is needed to combine these two different networks together. For users to be able to communicate with this hybrid network, they all must be supplied with a radio frequency detector, to communicate with Wi-Fi signals and a photo detector for the Li-Fi signals. A Hybrid system of this nature would bring many benefits in a working or home environment. Homes and offices already have light bulbs in place, a hybrid network would combine the availability, security and efficiency of Li-Fi, with the advantages provided from Wi-Fi. However, there are challenges to overcome a hybrid network like this would need to be an asymmetric network and these are the problems that can occur:

• Current network architecture requires downlink and uplink data streams between the client and server, must flow through the same routing path. This means that a coordinator acting as a transitional node is needed to alter the direction of the downlink data flow to a Li-Fi hotspot. This is where a problem occurs, adding an extra device to a traditional network framework is counterproductive as it requires a massive upgrade in hardware which is simply just not cost efficient.
• A router can be found almost everywhere in the modern world, they are used in homes, places of business, hospitals and even places of worship. Wi-Fi Routers connect local area networks (LANs) to wide area networks (WANs). So, any device connected to the same router is dispersed along the same subnet. The same routers IP address is assigned to the associated host as a gateway. A particular issue pops up in this case when averted information (or data) packets show up at the relaying node instead of the target destination.
• Out of all of the problems that come from using this type of hybrid architecture is an issue that occurs with the client. Normally a client triggers a TCP connection with a server by through the use of a three-phase handshake. According to the OSI model, first a connection establishment is requested, this segment is then created at the application layer. The segment is then encapsulated with IP and TCP heeders in the network layer, it is then transmitted though the NIC. When the request arrives at the server, a client will begin to listen to the socket with the matching IP address and TCP port number, waiting for a reply back from the server. The sent back packets with contrasting port numbers or IP address won’t be processed by the client that triggered the connection. This means that packets with errors cannot be identified by the client side application.

Practical Applications of Li-fi

Due to Li-Fi’s variance in features, there is a numerous amount of application for this technology. It can be applied in areas such as security, dense environments and in transportation systems etc. Each fixture of light within an application environment can become its own data channel, in each of these channels distinct data can transmitted through these pools of light .This section will give a summary of what these applications are and how Li-Fi can be applied to these fields:

1. Security

If you take the case of a study room environment, each channels access area within this room is the width of the light pool, also multiple users can access these channels. Every user will receive faster data rates than an equivalent Wi-Fi channel. This is because with Wi-Fi every user on the same channel is competing with other users for access of the bandwidth. In turn, this means that there are a lot more users connect thus making downloads speeds slower for every user. However when it comes to Li-Fi , access points are available in larger numbers, this allows for each pool of light to make available for use complete channel data rates with less users connecting simultaneously. This allows for every user to experience up to 1000 times greater speeds. To add to this point, unlike radio waves light cannot travel through walls. Meaning less security measures are needed to prevent the leaking of data from windows, making the security more secure than when dealing with Wi-Fi.

2. Dense Urban Environments and Cellular Communication

Urban Environments of the dense nature tend to some type of artificial lighting, mainly in the forms of streetlights or traffic lights etc. This Lighting framework can be used to provide cellar communication, Street lights could be used instead of radio base stations. Radio base stations usually have distances between them of around 300-500 meters. Street lights have much lesser distances than that of radio base stations, they could be used to provide illumination during the night time and simultaneously provide high speed communication all day and night. Even when the street lights appear to the eye to be inactive, data transmission is still possible. In addition when it comes to the homes of these dense environments, a desk lamp, or a home LED light bulb would act in the exact same manner. All rooms tend to have their own source of illumination, and since light cannot travel through walls, it leaves a nice interference free zone. In addition the spectrum does not need to be distributed amongst a large amount of users within a room.

3. Underwater Communications

Radio waves cannot travel far in water, they are quickly absorbed. Light communication can be used to allow connection from diver to diver

4. Transportation systems

As time passes all Vehicles are moving to fitting LED versions of their Headlights and taillights. This leads to the potential of vehicle to vehicle communication through Li-Fi. This means that anti-collision systems can be put in place, vehicles could swap information such as driving conditions. All traffic lights already use LED light bulbs, so a traffic management system could be deployed there. These vehicles could then use this traffic information, to have real time data on best routes to go down.

Simulation Results

Since Li-Fi is a new technology so simulating a scenario is slightly t difficult simply because most simulation software has simply no accommodated for this new technology. However Li-Fi is still a wireless technology, therefore the protocols that is uses will be the likely similar or very much the same as a Wi-Fi simulation. What this simulation will do is compare a Wi-Fi network and Li-Fi network both in a home environment. I will be looking at how packets perform within these networks and draw comparisons between Li-fi and Wi-Fi.

Wi-Fi simulation

In figure 2 a simple home environment Wi-Fi Topology has been created. We have various devices such as PC, a laptop, a smartphone and a tablet. All have been assigned with a static IP address. These devices are connected to a wireless access point, this wireless access point is then connected to a switch which is being used as the default gate way for all devices on this network including the server that is connect to the switch. The server has also been assigned its own static IP address.

Li-Fi simulation

As stated before Wi-Fi and Li-Fi have very similar topologies, the only difference a Li-Fi topology will have a lot more access points simply because a house will have a lot of lights which can act as the access point. In the figure below we can see 6 devices all connected and split through 3 access points. These access points (acting as LEDs transmitters in the case of Li-Fi) are all connected to the same switch, which is then connected to the server. Like before the server, switch and all devices on the network have all been assigned a static IP address with a subnet mask of 255.255.255.0 with the default gateway for each device being the switches IP address.

As done in the Wi-Fi simulation, packets have been sent from each device to the server, to show how long it takes for a packet to travel from a device on the network to the server

Discussion of results

The average time taken for each packet to reach the server for each device was calculated, then plotted against time. The results can be seen in the figures below.

As we can see from the results, when using a Li-fi network the speed of which packets take to reach the server decrease when compared to using a Wi-Fi network. Packet tracer does not allow for you to configure the access points to li-fi frequencies. So, the results that have been collected are a rough estimate. If it was possible to configure the frequencies that Li-fi use, as stated earlier in this paper the transfer time of packets will surely be faster. From the data gathered above we can see that in-home environments Li-Fi seems to be the most suitable. Why is this? Well in homes it is a lot more practical to use LED as an access point rather than using one router/access point for a whole household. There will be less traffic as not all devices are not trying to use the same point of access.

Conculsion

Li-fi has a vast amount of potential in the wireless industry, especially when it comes to implementing this technology in closed environments such as our homes and work places. But there are drawbacks to this technology. Since it does use visible light how would it work in countries who do not always have a source of LED light thus limiting the locations this technology can be used. visible light cannot penetrate walls meaning that Li-Fi signals range is limited by physical barriers unlike Wi-Fi, again limiting situations the technology can be used in. Interference can be caused by natural light or sunlight and would disrupt internet connection and would be very hard to deal with. A new infrastructure would be needed as well to support Li-Fi and this would be costly. To conclude, the future of Li-Fi as a standalone technology is not strong however more could be done with this technology if it used alongside Wi-Fi. They would support each other’s weaknesses and highlight their strengths. A better future awaits Li-Fi if it used in this manner.

References

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