A Survey of Cognitive Radio Systems
Croatian Post and Electronic Communications Agency, Jurišićeva 13, Zagreb, Croatia email@example.com
Abstract - A fundamental problem facing the future wireless systems is where to find suitable spectrum bands to meet the demand of future services. While essentially all of the radio spectrum is allocated to different services, applications and users, observation provide evidence that usage of the spectrum is actually quite low. In order to overcome this problem and improve spectrum utilization, cognitive radio concept has been proposed. This paper provides an overview of cognitive radio for opportunistic spectrum access and related research topics. Cognitive radio objective is to use scarce and limited natural resources efficiently without causing excessive interference to the primary licensed users. Consequently, cognitive radio has to sense and understand its spectrum environment, identify temporarily vacant spectrum, transmit adaptively and learn from its behaviour. A number of promising concepts for cognitive radio were briefly presented and discussed in this paper in the area of passive and active spectrum awareness, spectrum management and transmit
Keywords - Cognitive Radio, Opportunistic Spectrum Access,
Spectrum Awareness, Spectrum Management, Transmit Power
Radio spectrum is a valuable commodity, and a unique
natural resource shared by various types of wireless services. Unlike other natural resources, it can be repeatedly re-used, provided certain technical conditions are met. In practice radio spectrum can accommodate a limited number of simultaneous
users. Therefore, radio spectrum requires careful planning and management to maximise its value for all users. Currently,
spectrum regulatory framework is based on static spectrum
allocation and assignment policy. Radio spectrum is globally allocated to the radio services on the primary or secondary
basis. This is reflected in the Radio Regulations published by the International Telecommunication Union (ITU) , which
contains definitions of these services and a table defining their allocations for each of three ITU geographic world regions. On the European level, radio spectrum is governed in the European Union by the Radio Spectrum Policy Group (RSPG) and Radio
Spectrum Committee (RSC) and by European Conference of
Postal and Telecommunications Administrations (CEPT).
Additionally, national regulatory agencies define national
allocation table and assign radio spectrum to licence holders on a long term for large geographical regions on exclusive basis. Generally, user can use radio spectrum only after obtaining
individual license issued by national regulatory agency. In
technical point of view, this approach helps in system design since it is easier to make a system that operates in a dedicated band than a system that can use many different bands over a
large frequency range. In addition, spectrum licensing offers an
effective way to guarantee adequate quality of service and to prevent interference, but it unfortunately leads to highly
inefficient use of radio spectrum resource.
Analysing Article 5 of Radio Regulations , and national
allocation tables it can be concluded that usage of radio
spectrum bands is already determined. Furthermore, in national spectrum assignment databases almost all frequency bands of
commercial or public interest are already licensed. Current
predictions of further growth of demand for wireless
communication services show substantial increase in demand
of radio spectrum. All of this circumstances support raising serious concerns about future radio spectrum shortages.
Nevertheless, related radio spectrum observation surveys have proved that most of the allocated spectrum is underutilized
[2-8]. FCC's measurements in Atlanta, New Orleans, and San
Diego in 2002 revealed that there are large...
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