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220 From smart grid to internet of energy

6.3.1 Infrastructure-based (centralized) architecture
The structure of infrastructure-based (or centralized) CRN architecture that is
illustrated in Fig. 6.6 consists of the primary network and the secondary network
(the CRN). As stated earlier, the primary networks have priority for access the
licensed spectrum bands while the secondary networks (the CRNs) can only
access to the spectrum opportunistically [16]. A CRN including a cognitive
BS (CBS) is considered as infrastructure-based CRN (or centralized CRN).
The CBS behaves as a center gathering spectrum analysis information from
all CR devices, and decides how to prevent interference with the primary net-
works. In accordance with this decision, each CR device updates its system
parameters to continue data transmission. In addition, it is important to note that
a central AP may also undertake this coordinator task [59]. In this network
architecture, the CR devices can access both the CBSs and APs in a direct or
multi-hop way. The CR devices in the same network can connect each other
over the CBS/AP of the network. Communication among different networks
are realized over a backbone or core networks. In order to satisfy requests of
CR devices, the CBSs/APs carry out several transactions at the protocol layers.
Furthermore, several applications and networking systems can be established
by employing infrastructure-based network architecture. Moreover, the CBSs
and/or APs can execute different communication protocols and standards to
provide better services for CR devices. Conversely, the CR devices can connect
to different type communication systems with permission of their CBS/AP.

6.3.2 Ad hoc (distributed) architecture

The distributed CRNs can be taken into account as ad hoc or point-to-point
(P2P) communication systems in which the SUs can transmit their data over
licensed or unlicensed frequency bands in an opportunistic manner. A typical

FIG. 6.6 Infrastructure-based (centralized) network example for the CR systems.