Fig 1.1: Block Diagram Of Communication

Wireless communication is defined as the process of transfer of information from one point to more than one point without a physical medium. They uses radio waves for their transferring process because the distance of radio waves can be short, such as a few meters for television and even millions of kilometres for space communications. It has certain applications in fixed, mobile, and portable devices, including two-way radios, cellular telephones, personal digitalassistants (PDAs),and wirelessnetworking..Also.it.consists.of.certain.applications.include.GPSdevices ,computer.mice,keyboards ,headsets, headphones,satelliteTV , broadcast television an cordless telephones.The basic block diagram of wireless communication is shown in Fig(1.1).
It is defined as an electronic device which receives the radio waves and converts them into usable form of waves. The antenna is used for receiving the radio waves (electromagnetic waves) and converts them to alternating currents and give to the receiver, and the receiver extracts the desired information. The electronic filters in the receiver is used to separate the desired radio frequency signal from all the other signals picked up by the antenna, an electronic amplifier is used to increase the power of the signal, and finally recovers the desired information through demodulation. The receiver produced the information may be in the form of sound (an audio signal), images (a video signal) or data (a digital signal). A radio receiver may be electronic equipment, or an electronic circuit . Television sets, radar equipment, two-way radios, cell phones, wireless computer networks, GPS satellite dishes, radio telescopes, blue tooth devices, garage door openers etc. are the devices uses the radio receivers. There are many types of radio receivers which are used as the front end of the reconfigurable
Cognitive radio is the next generation of Software Defined Radio (SDR) which is slowly becoming more of a reality. This technology will be the more effective for radio communications systems .The idea for cognitive radio is to utilise the radio spectrum more efficiently, and to maintain the most efficient form of communication. By using the Cognitive Radio, it is possible detect the spectrum and frequencies are clear, and adapt best form of communication for that particular condition. It is also used for the process of selecting the frequency band, modulation type, and power levels which are suited for the requirements.
1.2 COGNITIVE RADIO HISTORY: There have been many factors that have lead to the development of cognitive radio technology. The requirement of the radio spectrum is improved with the drive for the improved radio communication and speeds. This leads to the efficient utilization of the radio spectrum and the associated cost which depends upon the amount of spectrum used. Along with this it provides greater communication flexibility in many instances. The example for the need of the flexible communication is occurred in the firework factory explosion happened in Netherlands in 2000 by killing 23 people, destroying almost the town and thousand people got injured. The emergency services i.e fire, medical and police will the difficulties in the communication due to