# Adaptive Data Synchronization Algorithm for IoT-Oriented Low-Power Wide-Area Networks
## 1 Introduction
In medical applications, healthcare remote monitoring represents a promising solution to facilitate the interaction between patients and doctors. In fact, parameters such as blood pressure, temperature, or respiratory rate can be easily measured at home by patients through medical wearable devices, and then sent to a cloud server to make them available to hospital personnel at any time [14; 15]. Monitoring activity also concerns industry, where production line control, inventory tracking and many other tasks can be performed in an automated and remote fashion. Finally, smart environment applications collect a wide range of activities to be handled, from traffic control, pollution monitoring \begin{table}
\begin{tabular}{p{142.3 pt} p{142.3 pt} p{142.3 pt}} \hline \hline
**IoT Scenario** & **Applications** & **Typical Traffic Volume** \\ \hline \multirow{4}{*}{_Healthcare_} & Respiratory rate & \\  & ECG & Tens of bits to a few kilobytes \\  & Blood pressure & per measure \\  & Skin temperature & (single/aggregate measures messages) \\  & Oxygen & \\ \hline \multirow{2}{*}{_Industry_} & Environment monitoring & \\  & Indoor localization & Tens of bits per message \\  & Production line control & \\ \hline \multirow{4}{*}{_Smart cities_} & Traffic management & \\  & Waste management & Tens of bits per message \\ \cline{1-1}  & Parking tracking & (aggregate data measures) \\ \cline{1-1}  & Pollution monitoring & \\ \hline \multirow{4}{*}{_Smart buildings_} & Lighting control & \\ \cline{1-1}  & Energy/water use & Hundreds of bits per message \\ \cline{1-1}  & Surveillance & (single/aggregate data measures) \\ \cline{1-1}  & Indoor climate control & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Typical IoT LPWANs use cases. and waste management in cities, to indoor lighting and climate control, energy and water use in buildings [16]. Overall, the diversity and specificity of each introduced application results in a largely variable exchanged data traffic volume. By looking, for instance, at the medical scenario, the data outputs of devices measuring blood pressure and heart rate are typically in the order of tens of bytes [17]. However, since these kinds of measurements are performed many times a day, it is possible to reach a daily aggregate data volume up to hundreds of bytes. On the other hand, processes such as electrocardiography (ECG) are more sporadic, but they can generate a large amount of information up to dozens of kilobytes [18]. Therefore, handling heterogeneous networks necessarily requests an efficient management of heterogeneous data. The main aspect characterizing LPWANs is the restrained power consumption that brings benefits in terms of battery life extension, especially for mobile entities. On the other hand, the limited rate makes data transmission slower than in other technologies, so devices may be forced to remain connected for a long time. Energy saving strictly depends on how long devices stay active within the network, therefore this issue may become very challenging in those IoT applications that consider low interaction among entities. Specifically, the problem of power consumption in IoT LPWANs can be identified at the following levels:  
* _network access and interference:_ some technologies such as NB-IoT work according to a random-access procedure where a sequence of signaling messages is sent by the user asking for the channel resources. This mechanism may request non-negligible power since, if the channel is busy for a long time, the number of signaling messages to be generated will increase. However, the advantage of NB-IoT is that the use of licensed frequency bands limits the problem of interference with other communications. This is not true when dealing with systems such as Sigfox and LoRa where the channel access is simpler than the NB-IoT, but on the other hand exploiting the unlicensed spectrum for transmission may lead to strong interference, resulting in possible data packet loss. In that case, the information must be retransmitted, thus causing additional power usage.