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Cognitive radio based smart grid communications Chapter 6 215

FIG. 6.3 Block diagram of the spectrum decision process.

determined channels. Process steps of the spectrum decision transaction are
depicted in Fig. 6.3.
Also, it is important to note that each CR device should present high flex-
ibility for system parameter update operation where several parameters such as
transmit power, carrier frequency, mapping method, bandwidth, and channel
coding schemes should be reconfigured to reach desired system performance
in terms of the QoS [31, 32]. Furthermore, CR devices may also alter their
access technology to further enhance the system performance [33].
Spectrum Sharing: This process is realized in cognitive media access control
(MAC) protocols. The spectrum allocation method, spectrum access mecha-
nism, and CRN architectures are crucial for spectrum sharing operation that
authorizes the SUs to fairly use the licensed spectrum bands. In addition, trans-
mit power level of the CR devices should be always limited to keep interference
under a particular threshold value. Spectrum sharing process can be performed
via two different ways. While one of them is called as centralized spectrum
sharing, the other one is distributed spectrum sharing. Whereas a central con-
troller manages the spectrum access and spectrum allocation processes in cen-
tralized spectrum sharing method [32, 34, 35], CR devices realize these
processes themselves in distributed spectrum sharing method [19, 34]. Even
though the centralized method presents higher performance than that of the dis-
tributed method, its disadvantages are increasing cost and higher system
complexity.
On the other hand, spectrum allocation process can be divided into two
groups as cooperative and non-cooperative technique [36, 37]. The former
method can provide better performance by ensuring cooperation between entire
active CR devices and primary networks, when it is compared with the latter
method. The CR devices serving with non-cooperative method have no collab-
oration with other CR devices and primary networks, and they strive to increase
their system performance as much as possible. Moreover, the cooperative
method also presents several advantages in terms of accuracy, spectral effi-
ciency and throughput. However, these advantages of cooperative method cause
increment in both cost and system complexity. Conversely, the main advantage
provided by the non-cooperative method is less energy consumption because of
lower complexity.
Spectrum Mobility: One of the most important processes for CR devices is
spectrum mobility that aims to autonomously change operating frequency of
CR devices to ensure uninterrupted communication. In other words, spectrum