# Design and Analysis of Adaptive Hierarchical Low-Power Long-Range Networks
## 1 Introduction, Related Work and Our Approach
On top of that, since IoT devices are operating in a low-power mode, listening to the communication channel for down-link messages is done occasionally, also severely limiting downstream message exchanges. Keeping in mind that many of the proposed applications require the deployment of _very large number of devices_, it is critical to propose certain extensions to existing LPWAN structures so that they can eventually accommodate very dense deployments of IoT devices without exceeding the capacity of the LPWAN [13, 14]. Typical examples of dense IoT deployments can be easily identified in the remote metering and monitoring domain like [9, 15, 16, 17]. Installation scenarios like this could include hundreds of connected meters installed deep inside buildings close to each other including both up-link and down-link transmissions or mobile devices that are installed on public buses, cars or bicycles that move throughout the city. Our work follows the same principles, organizing the network using hierarchical structures to reduce the number of the LPWAN enabled or equivalent devices within a certain area and consequently reduce the total number of devices accessing the sub-GHz spectrum. For example, the hierarchical solution can be used to reduce the number of LPWAN enabled meters to one per building or one per building block, thus helping to significantly reduce the overall cost of the network. End-level IoT devices, (e.g., inside a house) can communicate locally using non-LPWAN technologiesto exchange data and choose a nearby one that is capable of accessing the LPWAN network to relay their information to the local concentrator. Such a device can act as a local gateway or access-point, as it happens with the typical broadband modoms for homes or small enterprises. Other wireless technologies can be used to allow smart meters to forward their messages to the local LPWAN gateway and then to the rest of the network. In this work, an architectural organization of the IoT devices is introduced in order to increase the scalability of the LPWAN. In fact, since [18], grouping sensor nodes into clusters has been widely pursued by the research community in order to achieve network scalability. The main concept is to equip IoT devices with multiple network interfaces that enable both long-range and short-range communication. The architectural organization is achieved with appropriate levels of flexibility, in order to be able to accomplish the network's global goals and objectives. The IoT devices decide which of the multiple network interfaces to use by communicating, cooperating and forming adaptive sub-organizations. Such a solution can be used to increase the scalability of complex systems such as the one presented in [19]. In this system, multiple agents collaborate locally to decide the configuration of the HVAC (Heating, ventilation, and air conditioning) and environmental control inside an office. Using our system, the agents of the system can elect a local leader that is capable of communicating with external sources of information (e.g., a weather service) and is capable of aggregating all the choices of the inhabitants to reach a common agreement. The hierarchical network scheme presented here includes some of the concepts and ideas presented in [7; 20]. Like in [7], the network scheme uses the concept of grouping nodes; however, routing is not carried out through these groups of nodes by creating multiple hierarchical levels. In contrast, in this work, (a) the hierarchy introduced is limited to only two levels; and (b) the concept of nodes that have access to two networking technologies (802.15.4 and LPWAN) instead of only one. Furthermore, in this work, we employ a duty-cycling technique across both networking technologies in order to further conserve battery power among the devices. The combination of a power-conservation scheme with topology detection was not examined in either of the previous works.