Static And Dynamic Spectrum Allocation Computer Science Essay

atmospheric static And Dynamic Spectrum Al localization of function Computer scientific discipline EssayAs the requirements of the piano tuner gains keep growing, the number of line radio receiver standards increases, which consequently imposes increasing stress on the decided and check radio spectrum. However, extensive measurements reported indicate that large part of licence bands is in low usage, as show in Figure 2.1. Spectrum utilization is strongly depended on place and succession. Fixed spectrum apportioning wastes resources. 1Figure .1 Spectrum drillNowadays applications require more than bandwidth for better dish ups. Electromagnetic spectrum, however, is a anatomy of limited natural resource as well as pee and crude oil. Recent studies noted the poor utilization of conventional sole(a) spectrum identification. An intuitional way to improve the sparse usage is to go out an un certify user to access the resource during idle time. We notify improve effi ciency by aloneowing un accredited users to exploit spectrum whenever it would not cause duty tour to authorize users.2.2 Spectrum identification PolicyWhy A primed(p) spectrum fraction is assigned to licensed holders on a long term basis for large geographical regions. Figure 2.2 show fixed spectrum assignment to different standards.Figure 2.2 Spectrum fitting policyAccording to Federal Communications Commission (FCC), this exclusive assignment limits the usage and results in m any spectrum holes, also called white space. It shows most work over wireless network concent range on incident frequency, in token region, at particular time while a significant amount of the spectrum remains unused. Throughout the whole spectra, utilization varies from 15% to 85% in frequency, time and geographic domains. Much worse is that, 90% of the time, certain portions of licensed bands atomic number 18 unoccupied. As users demand for better quality of services and higher(prenominal) data rate, efficient spectrum usage is becoming a critical issue. 22.3 Static and Dynamic Spectrum Allocation in that respect has been numerous protocol standards on the wireless spectrum that rely on a static spectrum allocation policy on a lower floor which each licensed spectrum band is statically assigned to the specific licensed service and its users. Once a spectrum band is assigned to a certain service, its allocation is not allowed to change. However, a saucily concept of dynamic spectrum allocation has assoil necessary to overcome critical limitations of the traditional static al location scheme. Recent studies have shown that the use of static spectrum allocation has degraded phantasmal efficiency significantly. Moreover, current standards cannot guarantee the pr eveningtion of unexpected interruptions by wireless network users. To alleviate these problems, FCC has recently suggested a new concept of cognitive radio networks (CRNs) that serve wells as a framework in real izing dynamic spectrum allocation. It requires the enhancement of current PHY and MAC protocols to adopt spectrum-agile features. The basic idea of spectrum agility is to allow secondary users (genus Sus) or unlicenced users to access licensed spectrum bands as coldther as they do not produce undesirable interference with the licensed users. To achieve this goal, SUs necessity monitor each channels usage pattern by its sanies to identify spectrum holes or opportunities to exploit. Whenever SUs find a channel that can be utilized without interfere with its PUs, it can be assigned to and leave laughingstock be sh ard by the SUs. The SUs are also responsible for monitoring returning PUs on the channel they are currently victimisation so as to promptly vacate the channel in such(prenominal) a case. 32.4 unaccredited SpectrumThere are two major advantages of using unlicenced spectrum. First, thither is no requirement to register for using the spectrum and its deployment is v ery steadfast and salute effective as well. Second major advantage of using unauthorized spectrum is that it is shared among users which is indeed useful for wireless schemes in which devices can dynamically change its position like notebooks, cell phones, etc. It would not be practical to require the owners of a portable device to acquire a license that covers every place they may ever wish the system to operate. Fixed applications that transmit sporadically or at fluctuating rates can also make more efficient use of unauthorised spectrum when one is not transmitting, another can. It has been shown that cellular systems could carry significantly more traffic if they shared spectrum dynamically, profferd that competing firms are willing to adopt cooperative strategies that serve their common interest. Metropolitan area networks carrying bursty data traffic could expect even greater efficiency gains, if competing networks can be motivated to adopt such techniques. 112.4.1 ISM b andThe industrial, scientific and medical exam (ISM) radio bands were originally mute internationally for the use of RF electromagnetic fields for industrial, scientific and medical purposes other than parleys. Figure 2.3 shows spectrum of ISM band. 13Figure 2.3 ISM BandThere are many factors which raises interest for using these bands such as time consuming standardization. Also, 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. There is no license fee for this band and the devices using these bands are cost effective. Many wireless communication standards are aimed to use unlicensed ISM band because it is easier to coexist with active wireless networks than to assign a new separate empty spectrum. Currently most of spectrums for wireless communication are saturated. There are heavy interference and competition in ISM band because many wireless devices flo w into this frequency area. On the contrary, spectrums of TV broadcasting, digital TV and wireless microphone tend to abeyant depend on devices location or time. In TV broadcasting, the spectrum is nimble in TV broadcasting hours, but no one can use the spectrum when broadcasting signs off. Also TV spectrum is changed in compliance with localization. The 2.4 gigacycle per second ISM band has become particularly popular in end few years such as household and virtually all commercial buildings are likely to have equipment that operates in this band. Applications include wireless LANs, Bluetooth and infrared devices for short range communication and for Advanced Traveler knowledge and Management Systems like door openers for garage, home audio system, cordless phones, removed(p) control, etc.2.5 Wireless Regional field of view Network (IEEE 802.22)IEEE 802.22 Working root word came in to being in November 2004 with a purpose of making a standard for wireless regional area netwo rk (WRAN) capable of using cognitive radio engine room. According to its technical specifications, 802.22 WRAN systems will operate on the VHF/UHF TV bands ranging from 54 MHz to 862 MHz. The target of WRAN is to provide wireless broadband access with the average reportage radius of 33 km and can go up to 100km. The main target is to make unlicensed access to unused TV spectrum. In particular, 802.22 WRAN systems will be able to sense the spectrum, identify unused TV impart, and utilize these channels to provide broadband services for fixed wireless subscribers. While doing so, they must make sure that there is no undesirable interference with licensed users. Figure 2.4 shows the WRAN standards and application.8Figure 2.4 WRANIEEE 802.22 is a standard for Wireless Regional Area Network (WRAN) which uses unused spectrum (spectrum whole) in the TV frequency spectrum on a non-interference basis. This standard is developed with the intent to give broadband internet coverage in rural ar eas with acceptable performance comparing with performance of digital subscriber line and cable modems. The television spectrum was selected for this application due to its propagation characteristics. Cognitive radios will reuse TV spectrum in an opportunistic way by find if the channel is occupied before using it.2.6 SummaryDue to the fast 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 downstairs which each lic ensed 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 ofdynamic 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 exis ting wireless networks than to allocate new empty spectrum. Cognitive radio technology is being used in WRAN developed by IEEE 802.22 working sort out give broadband services in rural areas having the performance statistics parallel to DSL and cable modems by utilizing white spaces on non-interference basis.