## 5 Discussion
### Sensor Node Power Consumption  
versus _Notification Periodicity_  
A crucial performance parameter with deep implications in service availability and maintenance cost for a UAN class is sensor node average power consumption. Figure 4 illustrates this parameter for a representative module implementing an enabling technology of each type of UAN class, as a function of the sensor node notification periodicity. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & \multicolumn{2}{c}{**LR-WPAN (Figure 3a)**} & \multicolumn{2}{c}{**WLAN (Figure 3c)**} & \multicolumn{2}{c}{**NNO (Figure 3d)**} & \multicolumn{2}{c}{**SO**} & \multicolumn{2}{c}{**DTN (Figure 3e)**} \\ \hline  & **Backhaul** & Yes & No & No & No & Yes (intermittent) \\  & **expexpably dudged** & & & Yes (the sensor node & No (dployed by the & Yes (in public vehicles) \\  & **Category** & Yes & No (dployed a priori) & includes the gateway) & SIMRes operated) & \\
**Backhaul and gateway** & **Can be extended-based** & & & & & \\  & **by the municipality** & & & & & \\ \cline{2-6}  & **Can be extended-based** & & & & & \\  & **by the municipality** & & & & & \\ \cline{2-6}  & **Power solution** & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\ \hline  & **Latency (from sensor node & Milliseconds (per hop) & \textless{}Milliseconds (per hop) & Tens of seconds & Handbook of milliseconds & Minutes or hours \\  & **mode to gateway**) & & & & & to tens of seconds & Minutes or hours \\  & **Latency (from gateway & Minutes (Daby cycle period) & Minutes or hours (Daby cycle period) & Minutes or hours (Daby cycle period) & Minutes or hours (Time \\  & **tos sensor node**) & & & & \\  & **Permanent** & & & & \\  & **connectivity (sensor & Yes & Yes & Yes & Yes & No \\  & **node point of view)** & & & & & \\  & **Seensor node location** & & & & & \\  & **degree of freedom** & High & Medium & Medium/High & Medium & Low \\  & **supported by the LAN** & & & & & \\ \hline  & **Event-based** & & & & & \\  & **applications** & & & & & \\  & & & & & & \\ \cline{2-6} Smart City application support & **Notification periodicity** & & & & & \\  & **(based on sensor node & \textgreater{}10 s & \textgreater{}10 s & \textgreater{}1 h & (at 1 hbit/s) & 1 h to 1 day (dec to \\  & **power consumption**) & & & & & \\  & & & & & & \\  & & & & & & \\ \hline \multicolumn{2}{c}{**Additional services**} & No & Video, web access & Image transfer, web access & No & No \\ \hline \multicolumn{2}{c}{**Standardized communication protocols**} & Yes & Yes & Yes & No (in progress) & No \\ \hline \end{tabular}
\end{table} 
Table 2: Feature comparison of the main UAN classes. Each individual column is related with the corresponding set of protocol stacks shown in Figure 3. This table summarizes content from Sections 4 and 5. In this study, the sensor node is assumed to transmit a data unit in acknowledged mode (except for the SIGFOX SO UAN, whereby a unidirectional communication mode is offered, leveraging that several  
Figure 4: Sensor node average power consumption for representative enabling technologies of each UAN class, assuming periodic notifications. Note that the General Packet Radio Service (GPRS) MNO and the SIGFOX SO lowest data rate require notification periods greater than 10 s (see Figure 5). Figure 5: Latency of data transmitted by sensor nodes to their next hop for representative enabling technologies of each UAN class. base stations participate in signal reception) every notification period, and remain in sleep state otherwise. Average sensor node power consumption results were theoretically calculated on the basis of a power consumption characterization (in terms of current consumption and duration) of each state involved in the cycle that comprises the notification transmission and the sleep period, for each module considered. For the LR-WPAN UAN, the power consumption characterization was obtained from published empirical measurements of the CC2430 2.4 GHz IEEE 802.15.4 platform [42].