Page 260 - From Smart Grid to Internet of Energy

232 From smart grid to internet of energy

latency. As well as optical communication systems, cellular and WiMAX based
communication systems are also utilized to widen coverage areas of the WANs.
Typically, the WANs may almost cover thousands of square kilometers and can
present about 10 Mbps data rates [76].
In order to improve the use of spectrum bands in the SG communications, it
is believed that the CR is a promising technology for efficiently accessing and
employing spectrum bands [68]. In 2010, Ghassemi et al. [39] proposed the uti-
lization of CR technology in the SG systems. A typical CR based SG commu-
nication structure is depicted in Fig. 6.17. This approach includes a three-
layered hierarchical structure that is composed of HANs, NANs, and WANs.
This approach can also promote both energy-efficient designs and spectrum
efficient designs. Moreover, the CR technology encourages the use of high
bandwidths in the SG system applications that are required for conveying mas-
sive information including metering, monitoring and control information [68,
76]. The following sections present CR enabled networks in the SG
applications.

6.5.1 CR enabled home area networks
The block diagram of a typical CR enabled HAN architecture is illustrated in
Fig. 6.18. A HAN architecture carries out two important functions called
commissioning and control. The former is responsible for detecting new appli-
ances once they connect or disconnect from a HAN, and controls connecting or
establishing of a self-organizing network. The latter is responsible for ensuring
interoperability and manages the communication connections among devices in
the SG networks. The mentioned communication connections generally utilize
the unlicensed ISM bands. The popular technologies used in these connections
are IEEE 802.11 WLANs, Wi-Fi, Bluetooth, and ZigBee that is widely used in
the HANs due to the advantages of low cost and low power consumption. There-
fore, the ZigBee may lead to interferences to other devices functioning in the
license-free bands. The cognitive HANs that combine the CR with the ZigBee
(or with IEEE 802.15.4 standard) to operate in a dynamic spectrum access man-
ner may be a satisfactory solution in order to overcome this issue. Moreover, the
CR devices in the HANs can also employ licensed spectrums if these bands are
not in use by PUs. Consequently, the SG systems can efficiently present
enhanced services in terms of metering, monitoring and controlling thanks to
the CR technology. Sreesha et al. [77] reported to exploit wireless sensor net-
works (WSNs) with several changes in routing protocols in order to provide
spectrum and energy efficient designs in the cognitive HANs. Moreover, Aijaz
et al. [78] developed a MAC protocol for the CR systems that provides energy
efficiency in addition to provided high reliability.
The HANs can be constituted either mesh topology or star topology where
wired (i.e., PLC) and wireless communication technologies (i.e., ZigBee, Blue-
tooth, Wi-Fi, and CR) can be efficiently utilized [68, 76]. Therefore, an