## 5 Case Study
#### IEEE 802.15.4 Protocol  
IEEE 802.15.4/ZigBee standard is a modern wireless communication protocol. This protocol has a set of features that make it convenient to use with smart grid, including cheap price, low power consumption, low complexity, and good data rate. This protocol supports Carrier Sense Multiple Access (CSMA), which is used to access the medium with no collision. IEEE 802.15.4/ZigBee standard can be operated on various license-free frequency bands. These bands support different numbers of channels, data transmission rate, and different frequency ranges [64]. The available radio frequency bands that are supported by IEEE 802.15.4/ZigBee standard [65] are summarized in Table 6 along with their characteristics. In this work, we choose the 2.4 GHz band because it can operate on 16 channels with a higher data transmission rate equal to 250 Kbps, and very important thing; this band is allowed to be applied in Asia [66; 67].  
Different types of network topologies can be supported by IEEE 802.15.4/ZigBee such as star topology, peer to peer (mesh topology), and cluster tree topology [68]. The data frame structure that is supported by IEEE 802.15.4/ZigBee is summarized in Table 7. This structure consists of four parts including, MAC command frame, data frame, beacon frame, and acknowledgment frame. Based on Table 7, the MAC packet size that is supported by IEEE 802.15.4/ZigBee is equal to 127 bytes. In addition, 114 bytes are the maximum packet payload size that is supported by IEEE 802.15.4/ZigBee [53].  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Frequency** & **Area** & **Data Rate** & **Frequency Range** & **Number(s) of** \\
**Bands** & **Area** & **(Kbps)** & **(MHz)** & **Channel** \\ \hline
915 MHz & Australia, America & 40 & 902–928 & 10 channels \\
2.4 GHz & Asia, Worldwide & 250 & 2405–2480 & 16 channels \\
868 MHz & Europe & 20 & 868.3 & 1 channel \\ \hline \hline \end{tabular}
\end{table}
Table 6: A set of radio frequency bands along with their characteristics that supported by IEEE 802.15.4/ZigBee standard [67].  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Cognitive Area** & **Wide Area Network** & **Neighborhood Area** & **Home Area Network (NAN)** & **(HAN)** \\ \hline Network topology & Centralized & Centralized & Centralized/decentralized \\ \hline Spectrum band & Licensed band & Licensed band & Unlicensed band \\ \hline Favorable network protocol & WiMax, 3 GPP, RF Mesh, and satellite & 801.11 s, RF mesh WiMax, 3 G, 4 G and LTE & IEEE 802.15.4 \\ \hline Network users & Spectrum broker, NGWs & HGWs, NGW & Smart sensors/meters/actuators, HGW \\ \hline Featured strategy & Optimal spectrum & Hybrid dynamic spectrum & Cross-layer spectrum sharing \\ \hline Application & Demand Resource and load management & Advanced metering infrastructure, demand resource, and load management & Advanced metering infrastructure, demand resource, etc. \\ \hline Key techniques & Join spectrum management & Spectrum handoff, guard channel & Power coordination, access control \\ \hline \hline \end{tabular}
\end{table}
Table 5: Summary of the smart grid characteristics based on hierarchical communications infrastructure [62; 63].