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Radio wave was first predicted by James Clerk Maxwell in 1865(Ref). In 1887 a radio transmitter began working briefly, the first and at last that time was only one and anywhere in the world. It was located in the research laboratory of a young German physicist, Heinrich hertz and its transmission could be received over a range of only few meters. But today literally we have over ten million of radio transmitters worldwide, some with short range while some others with global and even extraterrestrial reach.
In 1985, Gullielmo Marconi demonstrated the feasibility of wireless communications by using electromagnetic waves. This waves consist of oscillating electric and magnetic fields in phase and also perpendicular to each other and to the direction of propagation. In 1906 the first radio broadcast was done by Regsnald Fesseden (Ref) to transmit music and voice over the air. In 1907, the commercial transatlantic wireless communication was laughed (ref). In 1946, the first public mobile telephone systems were introduced in several American cities. The first analog cellular system, the Nordic mobile telephone system (NMT), was introduced in Europe in 1981.the first cellular wireless technology was introduced in 1983, and the advanced mobile phone system (AMB) was deployed for commercial used.
Radio technology is concerned with the lower (in frequency) part of the EM spectrum. Wireless communication system are built based on the transmission of EM waves also known as radio waves with the frequency range from 3Hz-300GHz (ref). These waves are transmitted across the space and received through the antenna which transforms the radio frequency electrical energy to EM energy and vice versa. Radio waves with different frequencies have different propagation characteristics each of which is suitable for a long range communication and high frequency radio waves are more suitable for short range (nasir, 2008). The frequency of radio waves is further subdivided into a series of bands as shown in the table below
Due to rapidly demands of radio spectrum Fig and congestion of the bands, leads to problems such as electromagnetic pollution and interference. Electromagnetic pollution consists of all radio energy radiated other than as a necessary part of legitimate transmission REF radio spectrum conservation. This can be categorised into two broadly groups namely the natural, during the lightning strikes and the artificial by man made such as electrical equipments in our homes.
Interference, in the other hand can occur when the transmission of two or more transmitters reaches the receiver. At the receiver the transmission of one of the transmitter is needed and therefore, this may affect the responds of the receiver common example is the microwave ovum. Yet all this activities has to be contained within the radio spectrum band. And this can never be extended to meet the increase in demand of radio users. So at this very point there is a conflict between the need of growing, human and societal developments and limited, finite resources ââ‚¬"electromagnetic spectrum within which these needs must be contained. In deed there is real danger that the radio spectrum will be the first of our finite resources to run out, long before the oil, gas or mineral deposits (ref radio spectrum conservation)
So the question is that how can we provide an infinite supply of radio spectrum to the radio based services which is in demand in our society within these limitations?
Regulating radio spectrum is a valuable and is needed for economic, societal and technological reasons. Radio spectrum is a public resources used for wide varieties of services. Utilization of radio spectrum means emitting EM waves at radio frequencies (i.e. 30 KHz-300GHz) and interference may occur when two or more radio devices are transmitting at the same time over the same frequency. And therefore spectrum managements are required to control the transmission of radio waves to avoid electromagnetic interference and pollution with other wireless users. These regulatory bodies determine how a particular spectrum band could be used.
Governments agencies such as federal communication commission (FCC) in the U.S.A, the ARIB(Association of Radio Industries and Business) in Japan, and the CEPT(European Conference of Postal and Telecommunication Administration) in Europe used some certain techniques such as control and command model(REF) to allocate spectrum band to license user, so as to use the radio spectrum band under certain rules and regulations(eg spectrum etiquee) specifies by the government. While the exact frequency assignments differ, similar services tend to use the same frequency ranges all the world. There some spectrum band reserved for scientific, industrial and medical purposes refers to as industrial, scientific and medical(ISM) radio band.
The allocation of the spectrum broadly divided into two category:
1 The licensed spectrum
This is the spectrum allocated to the users under some authorised and rules and regulations of using the radio frequency band. Spectrum licensed come along with the frequency assignments. One of the advantage of licensed spectrum allocation is that the licensed user has exclusive access to the spectrum in a given defined area as such there would be interference protection. In the other hand the user might not be using the spectrum all the time and therefore the spectrum may stay for a given period of time in a location unutilised. Table below show some licensed spectrum allocation
Broadcast TV applications
1G and 2G cellular
Personal communications systems
Wireless communication services
Fixed wireless services
TABLE OF LICENSED SPECTRUM
2-The Unlicensed spectrum
In this case the user wireless transmitters are operating at a particular frequencies without rules regulations and authorisation binding the operations. It allow multiple users to operate at the same frequency as such no protection from interference. as shown in the table below
ISM band I
Cordless phone 1G WLAN
ISM band II
Bluetooth, 802.11b, 802.11g WLANs
ISM band III
U-NIII band I
Indoor systems 802.11a WLANs
U-NII band II
Short-range outdoor system, 802.11a WLANs
U-NII band III
Long range outdoor sytems, 802.11a WLANs
TABLE OF UNLICENSED SPECTRUM
This command and control based spectrum management can guarantee that the radio frequency spectrum will be exclusively licensed to an authorized user. But however it could leads to spectrum underutilization as shown in the report from spectrum policy task force(ref). the spectrum management in efficient usage arise due to the fact that an authorized user may not fully utilized the spectrum atll times in all locations
FREQUENCY COORDINATION AND NOTIFICATION
LEGAL AND REGULATORY FOUNDATION
Spectrum demand and usage
To meet the spectrum demand there was a request to the communication commission to change the spectrum management policy to make it more flexible. The recommendations to change the spectrum managements are as follows (ref)
1-improve flexibility of spectrum usage and to determine the amount of spectrum to be occupied
2-take all dimensions and related issues of spectrum usage into the policy
3-support and ecourage efficient use of the spectrum
All of the above objectives were to improve both technical and economic efficient spectrum management. To exploit these opportunities, the wireless transceivers need to be more intelligent to access the radio spectrum such an intelligent wireless transceivers is refered to as cognitive radio