# HARE: Supporting Efficient Uplink Multi-Hop Communications in Self-Organizing LPWANs
## 3 Scenarios and Requirements  
According to their own characteristic range and bandwidth capabilities with respect to other technologies, the main use cases to which LPWANs are addressed include security alarms, car park spaces, agricultural applications, smart metering, consumer electronics, and intelligent buildings. By way of illustration, in the ENTOMATIC EU-project [32] a network of wireless sensor nodes [33] periodically reports information on pest population density and environmental parameters, such as temperature and relative humidity. HARE is clearly aligned with typical LPWAN applications and circumscribes its suitability to those scenarios with special concern for energy efficiency, where device batteries are so limited that the establishment over time of a direct connection to the base station, or gateway, would greatly affect their lifetime. In this sense, Table 1 offers a comprehensive list of common requirements from use cases to which HARE protocol stack gives response in combination with the appropriate hardware. Assuming that this hardware provides good signal penetration, a single GW could serve up to thousand low-traffic devices within its given coverage range. Applications executed by STAs, in turn, follow a _continuous data delivery model_[34] for their sensed information, periodically delivering small amounts of non-delay sensitive data. Although not considered in the current article, future HARE developments will consider offering QoS in scenarios with miscellaneous sensors (continuous, event-driven, query-driven, and hybrid). As sensor nodes are scattered over large areas, sometimes with problematic access, self-maintenance of the system shall be a priority, capable of giving response to the following challenges:  
1. Node initiated network connection: once installed for the first time or relocated, any node shall initiate its association process through a simple action (for instance, pressing a button). 2. Self-configuration and management: with the aim of building a robust network, it shall adapt itself to environmental and/or topology changes without human intervention. 3. Battery lifetime maximization: LPWANs replace old monitoring systems consisting of assigning human resources to study in situ the behavior of one or more physical parameters. Therefore, maximizing battery lifetime in such systems is vital in order to justify their usage ahead of other methods. 4. Firmware distribution: any change in the network configuration or in the application purpose shall be remotely and easily distributed by the GW. Lastly, although the operating system of embedded sensor nodes is typically less complex than general-purpose operating systems [35], it shall cope with the high variety of resources to manage in this kind of devices (processors, memories, clocks, network interfaces, and so forth) and the demand of support for concurrent execution of processes (time synchronization, data acquisition, task scheduling, channel access, routing parameters, and so forth). Under these premises, Table 2 compiles some of the main use cases supported by the HARE protocol stack in five IoT representative sectors: home and industrial automation, public infrastructure, natural resources, and smart agriculture and farming. \begin{table}
\begin{tabular}{c c} \hline \hline
**Requirement** & **Value** \\ \hline Coverage range & Up to several km \\ Geographic coverage & Excellent even in remote and rural areas \\ Penetration & Good in-building and in-ground penetration \\ Device density (per base station) & High (up to thousand) \\ Power profile & Unassisted, battery-powered devices \\ Battery lifetime & From some months up to several years \\ Throughput & \(<\)100 bits/s \\ Latency & Non-delay sensitive \\ Mobility & Static devices \\ Cost & Low hardware and operating cost \\ Maintenance & Unassisted and self-organizing network \\ Delivery model & Continuous data delivery model \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Common requirements of HARE use cases.