Routing Strategies for LoRaWAN Multi-Hop Networks: A Survey and an SDN-Based Solution for Smart Water Grid

Low Power Wide Area Networks (LPWANs) are becoming the most suitable communication technologies in the Internet of Things (IoT) applications due to their low power consumption, long communication range and low cost. Currently, Long Range Wide Area Network (LoRaWAN) is one of the most popular LPWANs. Because it offers the possibility to build private networks with an open standard, LoRaWAN is the most deployed LPWAN solution. However, LoRaWAN supports only one-hop communication, that is, the end-devices are connected directly to the gateways. Since LoRa links can be kilometers long, its signals may undergo interference with other radio signals or encounter obstacles such as buildings, trees. In urban areas, to ensure that indoor LoRa devices can successfully transfer data back to remote gateways (GWs), a dense deployment of GWs is required. Unfortunately, the deployment of many GWs increases the network cost. Multi-hop communication can be exploited to increase LoRaWAN network coverage and packet delivery ratio (PDR) without deploying additional GWs. Therefore, in order to improve LoRaWAN performance, different routing approaches have been recently proposed aiming to create LoRaWAN multi-hop networks where some devices can play the role of relay nodes. However, in some use cases like Smart Water Grid (SWG), where nodes are buried underground inside the pipelines, the use of some SWG devices as relay nodes is not efficient in terms of energy consumption. In this paper, we first provide an in-depth survey on different routing protocols proposed for LoRaWAN multi-hop networks followed by a useful comparison between these approaches. Then, to enable efficient peer-2-peer (P2P) communication between end-devices in SWG, we propose a routing protocol based on Software Defined Networking (SDN) where some specific nodes called Relay Nodes (RNs) relay data from leakages detection nodes. In the case where a sensor detects a leak, a signal is sent to shut off the water valve automatically through our routing approach. Through simulations under LoRaSim, our proposed solution outperforms the standard single-hop network in terms of energy consumption and packet error rate. A range of issues, problems are provided and some research directions are suggested.