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Abstract: With the rapid growth of the mobile subscribers, need a proper mechanism to provide the efficiency and effective wireless communication service. The best alternative option is the Optical Wireless Data Communication System. It is cost effective and less power consumptions. There are many competitive advantages in Optical Wireless Data Communication over normal Radio wave communication. With the new technologies, in future this media will be the best data transmission media in this world over any other media.
With the rapid growth of information technology high speed data transmission plays an important role in people's lives. In order to provide network access in portable computers and devices it is important to consider about high speed wireless networks. According to the Wireless operations permit services, such as long-range communications, that are impossible or impractical to implement with the use of wires .
To transmission data over a wireless network, in normally using radio waves. But it is not the only method for that. For wireless transmission we can use optical signals as well. The optical wireless transmission is mostly suitable for non-public network, or a consumer communication network
An optical wireless (OW) communication system relies on optical radiations to convey information in free space, with wavelengths ranging from infrared (IR) to ultraviolet (UV) including the visible light spectrum .
By using optical wireless transmission, we can send data at a very higher rate, such as 1GB per second. And also it has better security. In optical wireless data transmission, the power consumption is very low, compared with the normal radio wave systems. Due to the rapid evolving of wireless networks and personal communicators the available spectrum for radio is becoming a scarce resource. There for the radio spectrum gets increasingly crowded and radio transmission technology always gets affected by electromagnetic interference.
The optical wireless transmission technology is a smart alternative to radio transmission system. It provides unlimited bandwidth because optical spectrum is universally available without frequency and wavelength limitations.
Optical wireless data transmission technology is more suitable for indoor wireless networks compared with radio wave system because radiation is normally reflected or absorbed by walls because of its short wave length.
2. Overview - Optical Wireless Data Communication
As a method of providing high speed wireless network connections, the optical wireless communication system was come.
Optical wireless communication system is having some competitive advantages. Those are,
Having a wide bandwidth and it can use for high speed data communications.
The component for optical wireless transmission systems are low in cost, therefor optical wireless communication systems are profitable.
The components for optical wireless transmission system are low power consumptions. There for optical wireless communication systems save power.
A light wave cannot penetrate the opaque objects such as walls. It is thought that the light wave is secured against eavesdropping; there for cell planning in networks is simple and easy.
The optical wireless networks occupy no radio frequency spectrum and it can be used where electromagnetic interference is strictly prohibited.
The light waves are worldwide unregulated by any law.
Because of these competitive advantages, optical wireless data communication system attracts much attention as a medium which can use for high speed data transmission.
However, there are few researchers in this field, and many problems which solved also remains. For an example, how to construct an optical wireless LAN, because of complexity of creating different channels, reflection on walls and other objects, it has become a challenge.
As we consider the Light Wave is the speediest thing in the universe. If we can transfer the data in that speed we can be satisfied because we are reaching the maximum speed.
Most of the times optical wireless communication uses in indoor activities. In indoor optical wireless data transmission systems utilizing white LDC lights is proposed. Whit LEDs are the devices which will be future lighting sources for indoor lighting. Then we can archive both lighting purpose and data transmission purpose from the same source.
3. Major Research in Optical Wireless Data Transmission Systems
With the rapid growth of the technology, people try to archive their needs and wants in an efficient and effective ways. When it comes to data transmission people want to communicate in high speed, with low cost and consuming low energy, as a result of that optical wireless transmission system invented.
In section 3.1 I'm going to discuss about General Perspective of Optical Wireless Data Communication.
In section 3.2 I'm going to discuss about Comparison between Light wave and Radio Media.
In section 3.3 I'm going to discuss about Optical Wireless Link Design.
3.1 General Perspective of Optical Wireless Data Communication
In the vision of future, mobile subscribers will increase. For their convenient need to be construct more wireless communication mediums. The cheapest way is Optical Wireless Communication medium. When considering the normal radio wave transmission technology, with the rapid growth of the mobile subscriber, available spectrum will be a scarce resource. There for application of radio wave system is already limited by this problem. There for the optical wireless communication system is an attractive alternative to radio wave transmission system, because of a virtually unlimited, unregulated bandwidth . An Optical Wireless Communication system has the advantage of requiring low cost and low power consumption components also .
When considering radio wave and optical wireless technology, optical wireless technology require more free space other than using fiber optic cables. Integrated technologies of radio and optical is illustrate in Figure 3.1.1 .
Figure 3.1.1: Integration of radio and optical Communication.
3.2 Comparison Between Light wave and Radio Media
When considering light wave and radio wave, light waves have several competitive advantages over radio waves. To transmit radio waves need a carrier signal, but light wave will be a carrier itself. To generate and modulate radio wave signals will more cost over light waves. Both waves are reflexive and absorbed by dark objects. Light wave spectrum is continuous. Therefor the bandwidth will be unlimited together visible and Infrared range. But radio wave spectrum is limited. Both types of waves can go through glasses and can't though walls or other opaque barriers. It is easy to secure transmission against casual eavesdropping in light wave transmission, ant it prevents interference between transmitter and receiver. Both light waves and radio waves required a wired connected backbone, to communicate between barriers. The characteristics of radio and light waves are compared in Figure 3.2.1 .
Figure 3.2.1 Comparison between radio and optical wireless systems.
3.2 Optical Wireless Link Design
Optical wireless links may employ various designs, and it is convenient to classify them according to two criteria which is shown in figure 3.3.1 
Figure 3.3.1: Classification of simple infrared links according to the degree of directionality of the Transmitter(T) and Receiver(R).
The special case is diffuse link, other can understand easily. In a diffuse link, it is guaranteed that a single path is always present, regardless of obstacles or people impeding the line of sight path. The penalty of diffuse transmission is a much reduced capacity compared with a line of sight link.
4. Applications of Optical Wireless Data Communication.
The very basic application of the optical wireless communication is Traffic Lights. But today there are many complex applications in optical wireless data transmission. Basically optical wireless systems are classified into two categories depending on where the system is utilized. Those are Indoor Applications and Outdoor Applications.
4.1 Indoor Applications
This is a growing interest in indoor wireless networks as a consequence of the large scale utilization of personal computers and mobile communicators. In this applications, an optical wireless communication system is a candidate for the media of wireless networks. Infrared is preferred as wavelength in these applications, originally. This is because essentially a large total transmission bandwidth is possible, facilitating fast transmission systems due to the very high frequency involved in optical carrier.
4.2 Outdoor Applications
Over long distance optical wireless solutions can offer very rapid provision of exceedingly high bandwidth, at least 1 GBpS is easily achievable. This flexibility is brought at the price of increased downtime, due to occasionally unfavorable atmospheric conditions.
Some fixed services such as broadband signals from the curb to the home. The cost of this is dominated by two factors. The customer laser and receiver cost, and the cost of actually installing the fiber by digging or tunneling. This cost problem is known as "Last one mile problem". In Japan Optical Beam Networking council was established in 1997, so that the last one mile problem would be solved and optical transmitters and receivers are utilized .
5. Future directions of Optical Wireless Data Transmission.
The newest trend is using mobile devices. With the rapid growth of the mobile device usage, there should be an efficient and effective wireless data transmission mechanism. The best solution will be Optical Wireless Data Transmission system.
Because light waves are cost effective and less power consumptions. Therefor in future main transmission medium will be Optical Wireless Data transmission systems. And also we can generate unlimited virtual bandwidth using light waves. There for it can bear the rapid growth of mobile service requirement. So in the future, the Optical Wireless Data transmission systems will run the all communications.
In this paper I have given an introduction what is the Optical Wireless Data Communication is. Then I have given a general perspective about optical wireless data transition. Then I have given a comparison between light waves and radio waves. Then I have discussed about Optical Wireless data links and how they are categorized. Then I have discussed about what are the main applications of Optical Data transmissions. Basically I have discussed about Indoor applications and Outdoor applications. Finally I have given my idea about how the Optical Wireless transmission will act in future.
First of all, I would like to give my heartiest thanks to my supervisor, Mr. Shalinda Adikari. His wide knowledge of wireless communication and industry experiences has been of great value for me. His understanding, encouraging and personal guidance have provided me to a good basis for doing this. And also I would like to thanks to my friends and some nonacademic staff members, who helped me to do this.