There are two major advantages of using unlicensed spectrum. First, there is no requirement to register for using the spectrum and second its deployment is very fast and cost effective. Second major advantage of using unlicensed spectrum is that it is shared among users which are indeed useful for wireless systems in which devices can dynamically change its position like notebooks, cell phones, etc. Moreover, itâ€™s not possible practically that the user of portable device acquires a license that will serve at every place. 
Unlicensed spectrum access is openly available but it has strict laws and regulations for utilizing the spectrum. The access to unlicensed spectrum is available for any device but how the device will utilize the spectrum is controlled in a way that others devices will not be effected. The access to spectrum is allowed for only those devices which can follows standards of communication to minimize potential interference. 
2.4.1 ISM band:
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The industrial, scientific and medical (ISM) radio bands were originally dedicated for the use of RF electromagnetic fields for industrial, scientific and medical research purposes only, not for the field of communications. Figure 2.3 shows spectrum of ISM band. 
Figure 2.3: ISM Band
Since there is no license fee for using ISM bands so devices using these bands are cost effective. Moreover there is no requirement of registering the users using these bands, no particular restrictions on users for their usage and users can use the products anywhere at any place.
Most of the spectrum for WCS is already saturated and several new wireless technologies tend to use the ISM band since it is easy to exist in the free band rather than assigning a separate portion of spectrum for new services. So in this band there is a heavy competition for using ISM bands which can also cause interference problems. On the other hand TV broadcasting bands are used only in broadcasting hours and remains inactive rest of the time and no one can use this band in this inactive time which makes this band underutilized.
ISM band of range 2.4 GHz is becoming more and more popular for household devices in the last few years and almost all the commercial areas and building are also equipped widely with these devices such as garage door openers, chord less phones, remote controls, Wi-Fi hot spots and many short range Bluetooth and Infrared devices.
2.5 Wireless Regional Area Network (IEEE 802.22):
IEEE 802.22 Working Group was started in November 2004 for developing a standard for Wireless Regional Area Network (WRAN) which can also accommodate new technologies like Cognitive Radio. The 802.22 WRAN group is designed to work from 54 MHz to 862 MHz range which is VHF/UHF TV operating bands that has been underutilized in the past. The WRAN targets to provide wireless broadband internet access having range from 33 km to 100 km. The WRAN aims to utilize unused TV spectrum by making unlicensed access of TV spectrum. The new 802.22 WRAN system have the capability to sense the spectrum, scan for unused TV spectrum and then use that spectrum for providing broadband services. While doing so, they must make sure that there is no undesirable interference with licensed users. These all are main features for cognitive radio. Figure 2.4 shows the WRAN standards and application. 
Figure 2.4: WRAN
IEEE 802.22 WRAN standard is developed with aim to provide broadband internet services in rural areas with performance comparable with DSL and cable modems. UHF/VHF television spectrum is suitable for such service due to its propagation characteristics
Due to the rapid growth of wireless services, various wireless standards have been developed which are becoming a cause of major stress in fixed and limited spectrum. However fixed spectrum results in low utilization of spectrum resources as per the spectrum assignment policy. Now days, applications require more spectrum for efficient services. The fixed spectrum is not convenient for these services. Therefore, this problem can be improved efficiently by allowing unlicensed users to exploit spectrum whenever it would not cause interference to licensed users. The fixed spectrum policy that relies on a static spectrum allocation policy under which each licensed spectrum band is statically assigned to the specific licensed service and its users and its allocation is not allowed to change. In order to solve this issue a new concept of
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Marked to Standard
dynamic spectrum allocation also known as unlicensed spectrum policy has become necessary to overcome critical limitations of the traditional static allocation scheme. To make this concept more efficient, a new technology called cognitive radio technology has been developed. The basic idea behind this technology is to allow secondary users (SUs) to access licensed spectrum bands as far as they do not cause any harmful interference with the primary users (PUs). The unlicensed spectrum has two major advantages i.e., one is they are fast and cheap in deployment and other is unlicensed spectrum is shared. As sharing is essential for wireless networks, many wireless communication standards are aimed to use unlicensed ISM band because of complete absence of user restrictions and it is easier to coexist with existing wireless networks than to allocate new empty spectrum. Cognitive radio technology is being used in WRAN developed by IEEE 802.22 working group give broadband services in rural areas having the performance statistics comparable to DSL and cable modems by utilizing white spaces on non-interference basis.