# Performance Evaluation of a Mesh-Topology LoRa Network
## 4 Current Research  
Several recent research publications have suggested LoRa-based multi-hop routing topologies for LPWAN applications to further extend the capabilities of these networks. They typically focus on improving aspects such as power consumption, coverage, and scalability. This section only covers a small overview of the current research in the field of multi-hop LoRa; however, a more comprehensive overview of the current research can be found in [17]. Furthermore, the authors in [18] provide an overview of the latest studies, based on four main categories: energy-awareness, concurrent access and duty-cycle regulations, routing protocol, and security. \"LoRa for the Internet of Things\" [12] was the first published research paper to propose a multi-hop LoRa network. The authors proposed LoRaBlink, which was designed for reliable and energy-efficient multi-hop LPWAN communication. In this study, devices transmitted up-link packets in a staggered, slotted pattern to minimise power consumption and packet collisions. A flooding approach was used to organise the network routing. Six nodes and a gateway were deployed in an urban environment, and a packet delivery ratio of 80% was measured throughout the test. This was an improvement over a standard LoRaWAN, as some of the nodes were not able to reach the gateway through a single-hop up-link transmission. In [19], the authors proposed a novel low-cost, peer-to-peer, multi-hop, and gateway-free LoRa-based mesh LPWAN. The research article proposed moving away from gateways as the central role as concentrators and rather relying on a peer-to-peer-based network. The advantages of such a network are the improved security, as no information needs to be relayed through a network server, and improved performance, as no fixed central gateway is required (for example, in the case of first responders in a remote location). The authors in [20] proposed a novel gateway-centric mesh routing topology and simulated the performance in an OMNET++ simulation model. The research specifically focused on the packet delivery latency and packet delivery ratio. Nodes are assumed to be in Rx mode continuously and transmit in a pure ALOHA fashion. All devices in the network are assumed to be using the same spreading factor, and the routing model is optimised to minimise path loss between nodes. The simulation model showed a >98% packet delivery ratio for a network containing 40 nodes with a single gateway. The authors of [21] assessed a Distance-Ring Exponential Stations Generator (DRESG) where nodes in a multi-hop network are assigned to a ring, based on the distance to the central gateway. The study considers three routing topologies and evaluates each topology based on the complete network's energy efficiency and the node load balance amongst all the nodes in the network. The three topologies considered were a single-hop, where nodes transmit directly to the gateway, a next-ring hop, where nodes transmit directly to their parent node in the adjacent ring closer to the gateway, and an optimal-hop routing, where nodes transmit relay messages to a ring to minimise bottleneck nodes. The authors created a Matlab-based simulation model of the proposed routing schemes, with a layer of abstraction where various low-power sub-GHz transceiver models can be used, including LoRa. Each node in the network generates a data payload with a fixed size and fixed packet header. Static routing and negligible idle, sleeping, and microprocessor currents are assumed. A basic Time-Division Multiple Access (TDMA) MAC protocol was used to enable slotted communications between children nodes and parent nodes. The simulation model used an 802.11 ah pic/hot zone deployment path loss model, as defined in [22]. Data aggregation was used per ring, where data received from the children nodes were combined with the routing node's own data. The routing results highlight the high power consumption of nodes furthest from a gateway in a single-hop network, due to the high transmission power required.