# Adaptive Data Synchronization Algorithm for IoT-Oriented Low-Power Wide-Area Networks
## 4 Adaptive File Synchronization
### On Double Signature Efficiency
Specifically, the average data traffic reported in Table 2 has been considered as the transmitted data volume \(D_{s}\). Concerning the other parameters \(P_{tx}\) and \(v_{UL}\) introduced in Equation (8), we refer to the most popular LPWAN technologies on the market, namely Sigfox [7], LoRa/LoRaWAN [39; 40], and NB-IoT [10] (Table 3). Therefore, we have evaluated the DIoT energy consumption of a single synchronization procedure for different algorithms as shown in Figure 9, with the error bars referring to a 95% confidence interval. Finally, the measures reported in Figure 9 have been exploited to estimate the battery lifetime following Equation (9). Regarding the battery parameters, we have chosen \(C=27.7\) Wh and \(SF=1/3\) as in [38; 41]. The background device power consumption has been neglected to make the analysis specifically referring to the data exchange context. Furthermore, we have considered the scenario where a file synchronization procedure is performed once a day, thus returning a \(t_{e}=24\) h. Therefore, the battery lifetime, expressed in years, is described in Table 4 as a function of the considered LPWAN technologies and file synchronization algorithms. Figure 8: Chunk dimension adaptation as the synchronization events occur. By jointly observing the results in Figure 9 and Table 4 it is possible to appreciate how the data traffic saving provided by AC-_driff_ and AH-_driff_ returns, as expected, significant benefits in terms of DioT energy consumption. Furthermore, it is also evident that the amount of data exchanged impacts on the performance of the employed LPWAN technology. In fact, traffic volumes in the order of kilobytes (as considered in the simulations) makes use of Sigfox unfeasible since the very low data rate characterizing this technology unavoidably leads to long transmission times and, therefore, to high power consumption. On the other hand, LoRa/LoRaWAN and NB-IoT are better suited to the considered traffic volume. However, the presented scenario with 3 kB files daily updating is quite unusual in the IoT, since the amount of exchanged data is typically much lower. We have intentionally chosen this framework to stress the performance provided by the proposed synchronization algorithms. Moreover, considering more realistic circumstances where the daily traffic volume is in the order of a few hundreds of bytes, the battery lifetime values in Table 4 will increase, reaching the 5-10 years life usually claimed for IoT devices. \begin{table}
\begin{tabular}{l l l l} \hline \hline  & **Sigfox** & **LoRa/LoRaWAN** & **NB-IoT** \\ \hline _rsync\({}_{32,128}\)_ & 0.10 & 0.85 & 0.39 \\ _rdiff\({}_{32,128}\)_ & 0.12 & 1.10 & 0.50 \\ _rdiff\({}_{16,64}\)_ & 0.15 & 1.34 & 0.62 \\ AC-_rdiff\({}_{16,64}\)_ & 0.17 & 1.47 & 0.68 \\ AH-_rdiff\({}_{16,64}\)_ & 0.17 & 1.50 & 0.69 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Device battery lifetime, measured in years, considering the scenario where the 3 kB file synchronization is performed once every 24 h. Results are shown as a function of the LPWAN technology and file synchronization algorithm. Figure 9: Power consumption, measured in milliwatt second, of a single synchronization procedure considering different LPWAN technologies and algorithms. ## 7 Conclusions

This paper dealt with data synchronization in IoT LPWANs. In this context, two adaptive algorithms, namely AC-_rdiff_ and AH-_rdiff_, have been presented to optimize the amount of data to be exchanged when the synchronization between a DIoT and the Cloud is performed. The aim is to reduce the amount of traffic exchanged, still preserving the ideal synchronization, thus saving energy and increasing the DIoT lifetime. The performance analysis here reported has highlighted a significant traffic volume saving when the proposed algorithms are used with respect to other solutions currently adopted in remote synchronization.