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218 From smart grid to internet of energy

the wide areas, communication systems that provide the desired perfor-
mance should be as cost-effective as possible. Combining monitoring sys-
tems and sensors with the CRNs can also improve the monitoring features of
the SG systems. Therefore, the power outages can be significantly reduced
through the CRNs [47, 57].

6.3 CR network architectures

Diversity in spectrum policies and communication technologies is one of the
most important characteristics of the conventional wireless networks [58]. Sev-
eral sections of spectrum are allocated for licensed communication systems
whereas there still exist unlicensed spectrum bands. Hence, a good character-
ization for CRN architectures is required to improve communication protocols
for these networks. To ensure reliable communication through CRNs, the CR
devices should always track the network status and radio environment by pro-
viding coordination among the CR users. The mentioned coordination may
cause some problems since the spectrum is time-dependent, and the CR users
are generally mobile. The CRNs contain several types of radio communication
systems operating together in the same geographic areas. Therefore, the CRNs
can be taken into account as a kind of heterogeneous network containing numer-
ous wireless communication systems. This diversity may be originated from
connections among the base stations (BSs), access points (APs), mobile termi-
nals (MTs), networking protocols, and CR terminals. Terminals and service
providers can use the diversity of wireless access technologies. The CRNs
authorize the users to continuously utilize spectrum bands. The main design tar-
get of the CRN architectures is to improve the use of communication networks.
From the point of view of the users, the network usage indicates to accomplish
place and time independent wireless communication through the CRNs. In
terms of operators, the service providers should not only be obliged to provide
high quality service to mobile users, but they should also use network resources
efficiently and effectively [15]. A typical architecture of CRNs that is illustrated
in Fig. 6.5 contains several elements regarding both the PU networks and the SU
networks.
Typically, a primary network can be composed of PUs and primary BSs
whereas a secondary network contains ensemble of the SUs with or without
a secondary BS, as can be seen from the figure. A secondary BS that serves
as the center of the secondary network generally arranges the OSA for the
SUs. When various secondary networks employ the same spectrum band, a cen-
tric network equipment called spectrum broker manage the use of this spectrum
band. This equipment gathers operation information from secondary networks
and assigns the spectrum effectively and fairly. The network architecture
schemes of the CRNs can be classified into three categories as
infrastructure-based (centralized), ad hoc (distributed), and mesh architectures.
The following subsections introduce these architectures in detail.