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Cognitive radio based smart grid communications Chapter  6 221





















             FIG. 6.7 Ad hoc (distributed) network example for the CR systems.


             scheme of distributed network architecture is depicted in Fig. 6.7. This network
             architecture is essentially developed for supporting special-purpose applica-
             tions. In addition, the spectrum access decisions that are created depending
             on the local information may not be optimum in this type of network architec-
             ture. The CR devices can expand their network information by sharing locally
             gathered data among themselves, and the devices realize their transactions
             depending on these sensed global information. The communication among
             the CR devices can be also organized by employing various network protocols
             and standards (i.e., Bluetooth, GSM, Wi-Fi, etc.). Different distributed network
             architectures may be available and each of them requires specific protocols for
             the CR devices. The SUs can continue their communication by using cooper-
             ative communication methods over both licensed and unlicensed frequencies
             thanks to only one transceiver. It is worth noting that a CR node belongs whole
             CR capabilities and has to decide its subsequent actions considering observed
             local information in this network architecture.


             6.3.3  Mesh architecture

             A combination of infrastructure-based and distributed architectures constitutes
             the mesh network architecture. A typical mesh network is illustrated in Fig. 6.8.
             This architecture authorizes users for both transmitting and receiving data
             between CR devices, APs and CBSs.
                Each CR device not only behaves as a transmitter but also behaves as a
             router to control transmission of data packets. Thus, the CR devices may reach
             CBSs and/or APs directly or by employing cooperative communication
             methods in multi-hop manner. In addition, CBSs and APs generally operate
             as gateways to link the wired and wireless backbone networks together. Hence,
             this scheme is more secure and cost-effective than that of the other network
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