## 3 Physical (PHY) Layer and Media Access Control (MAC) in IoT
### Data Rates in IoT  
The physical layer of IoT is responsible for variable data rate support. As mentioned earlier, the technological diversity of IoT makes it versatile for the efficient utilization of resources including bandwidth and battery constraints. For this reason, a single technology like ZigBee operates at three different data rates, i.e., @250 kpbs on 2.4 GHz, 40 kbps on 915 MHz, and 20 kbps on the 868 MHz channel. Transmission rates for different technologies that are employed in IoT are given in Table 2.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Technology** & **Sub-Category** & **Operating Frequency** & **Data Rate** \\ \hline \multirow{8}{*}{Wi-Fi} & 802.11a & 5 GHz & 54 Mbps \\ \cline{2-3}  & 802.11b & 2.4 GHz & 11 Mbps \\ \cline{2-3}  & 802.11g & 2.4 GHz & 54 Mbps \\ \cline{2-3}  & 802.11n & 2.4 \& 5 GHz & 600 Mbps \\ \cline{2-3}  & 802.11 ac & 5 GHz & 1.3 Gbps \\ \cline{2-3}  & 802.11 ah & 2.4 \& 5 GHz & 347 Mbps \\ \hline \multirow{4}{*}{ZigBee} & \multirow{4}{*}{802.15.4} & 868 MHz & 20 kbps \\ \cline{2-3}  & & 915 MHz & 40 kbps \\ \cline{2-3}  & & 2.4 GHz & 250 kbps \\ \hline \multirow{4}{*}{Z-Wave} & \multirow{4}{*}{G.9959} & 868.42 MHz & 9.6 kbps \\ \cline{2-3}  & & 908.42 MHz & 40 kbps \\ \cline{2-3}  & & & 721 kbps \\ \hline Bluetooth 1 & \multirow{4}{*}{802.15.1} & \multirow{4}{*}{2.4 GHz} & 2.1–3 Mbps, 25 Mbps (+HS Wi-Fi) \\ \cline{2-3}  & & & 2 Mbps \\ \cline{2-3}  & & LoRa:SF12 & \multirow{2}{*}{125 kHz} & 250 bps \\ \cline{2-3}  & & LoRa:SF7 & & 5.47 kbps \\ \cline{2-3}  & & LoRa:SF12 & \multirow{2}{*}{500 kHz} & 980 bps \\ \cline{2-3}  & & LoRa:SF7 & & 21.9 kbps \\ \hline \hline \end{tabular}
\end{table}
Table 2: IoT technologies comparison with respect to their data rates.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \
\begin{tabular}{c} **Characteristic \(\rightarrow\)** \\ Level \(\downarrow\) \\ \end{tabular} & **Availability** &
\begin{tabular}{c} **Data** \\ **Transfer Rate** \\ \end{tabular} & **Node** & **Range and** & **Data** & **Power** & **Size of** \\ \cline{2-6}  & & **Transfer Rate** & **Mobility** & **Coverage** & **Security** & **Consumption** & **Devices** \\ \hline \multirow{4}{*}{Low} & Bluetooth, RFID, & Bluetooth, & Wi-Fi, Bluetooth, & Wi-Fi, Bluetooth, & Wi-Fi, Cellular & Bluetooth, RFID, NFC, \(Z\)-Wave, & Wi-Fi, Cellular & Bluetooth, RFID, NFC, \(Z\)-Wave, & Bluetooth, RFID, NFC, \(Z\)-Wave, \\ \cline{2-6}  & NFC, \(Z\)-Wave, & RFID, NFC, & RFID, NFC, & Fiber, Bluetooth, LoRa & ZigBee, Sigfox, & ZigBee, Sigfox, \\ \hline \multirow{2}{*}{High} & Wi-Fi, Cellular & Wi-Fi, Cellular & Cellular & Cellular & Cellular & RFID, NFC, \(Z\)-Wave, Sigfox, & Wi-Fi, Cellular \\ \cline{2-6}  & Network, & Wi-Fi, Cellular & Network, & Network, Sigfox, & LoRa & ZigBee, Sigfox \\ \hline \hline \end{tabular}
\end{table}
Table 3: IoT technology categorization with respect to its physical characteristics.  
The smart city applications vary the requirements for communication, and most of the time, we do not use frequent data transfers. Table 4 gives a detailed overview of the communication specifications in enabling smart cities. Note that these specifications are for the Padova Smart City project [28].