1 CHAPTER 1 INTRODUCTION 1.1 GENERAL Communication is sharing of thoughts or information from one subject to another subject. The subject may be a human being, animal or bird, even it can be a tree. The recent research studied by Gagliano (2012) says that trees are communicating one another. Very long ago human beings communicated very first through drawing an image or picture on a rock. They used some kind of sounds like birds and animals. Later sounds got evolved into a natural language when they were capable of writing a symbol or script for a particular sound. The people, at a hand stretch distance, communicate directly. Various forms of communication were used to convey the information to a remote location. The Marathon was one of the examples of remote communication as stated by Professor Theodore (2001). Ancient kings used pigeons to carry the message from one region to any other region, which was far away from where they used to live. Day by day, human culture, tradition and civilization had changed. Postal service, telegram, radio and television are used for communication. In this information age, the way information shared among people, is a wonder. The most appreciated invention is computer and one of its major applications is the Internet. Because of the Internet the world is called global village where people are very close to one another. The Internet is defined as the network of networks in which all computers can be connected to each other. The communication
2 through computer network can be done by two media namely wired communication and wireless communication. 1.2 WIRED COMMUNICATION Wired communication is a very first method that uses electronic devices in which communication signal is transmitted from source to destination through some media like coaxial cable, fiber optics. The media are also multiplexed mostly to enhance the bandwidth of the transmission line. The possibility of signal loss in wired communication is lesser than that of wireless communication. Cable communication, telephonic communication and fiber optics are some of the examples of wired communication. 1.3 WIRELESS COMMUNICATION The developments in electronic communication evolved into a big status, which resulted in the signals in the form of electromagnetic waves transmitted from source to destination without a wire. Leiner et al (1987) introduced Defense Advanced Research Project Agency (DARPA) radio packet networks, which were first the deployed wireless network. Wireless communication is carried out based on the principles of broadcast and reception of electromagnetic waves. Like wired media, wireless communication is also carried out through several multiplexing techniques. The low frequency band consisting of radio, microwave and infrared is widely used in wireless communication. Satellite communication, mobile communication, VANET, wireless sensor and MANET are a few examples of wireless communication.
3 1.3.1 Signal Propagation Electromagnetic waves are easy to generate and widely used for both indoor and outdoor communication. They are capable of passing through the building and the ability to travel long distance. Signals are transmitted omnidirectional. It is meant that they are spread out from the transmitting antenna in all directions. Signals in wired networks, travel along the wire and they exhibit almost the same behavior and characteristics at each point. For wireless transmission the behavior and characteristics are different at each point between the source and destination. The Figure 1.1 drawn below depicts the transmission behavior of wireless media. Distance Sender Transmission Detection Interference Figure 1.1 Signal propagation range Transmission rang is the undisturbed area with a certain range of the radius, a sender is very much capable of sending signals and a receiver is very much capable of receiving signals with a negligible error rate. In this range signal can be free from external noise .Detection range is the partially
4 disturbed area with a second range of radius. In this distributed area signals can be differentiated from background noise, but the error rate is too high to make effective communication. Interference rang is the fully disturbed area with a third range of the radius. In this interference range the transmitted signals are mingled with background noise and a receiver cannot detect the signals. 1.3.2 Path Loss of Radio Signals When electromagnetic signals travel in its wireless path, it has to suffer from various kinds of path loss. The properties of electromagnetic waves are as similar as the properties of light. In free space electromagnetic waves propagate at a speed as light waves do. They travel in a straight line. If such a straight line appears between a sender and receiver then it is called line-of-sight. Even if it travels in free space, the signals suffer from free space loss. MacDonald (1979) studied that the power of transmitted signal loosens its strength with respect to distance. The received power Pr is proportional to 1/d2 where d refers to the distance between sender and receiver. This is what called the inverse square law. The Pr also depends on the wavelength and gain of receiver and transmitter antennas and expressed in Equation (1.1) below 2 Pr where Pt Gt Gr 4 d Gt is the transmitter antenna gains Gr is the receiver antenna gains Pt is the transmitter antenna power and is the wavelength of the signal (1.1)