# Design Considerations and Performance Evaluation of Gossi Routing in LoRa-Based Linear Networks
## 3 Motivation  
The feasibility of LoRa as a relay technology has been proposed in various IoT applications. Our focus was to consider LoRa as linear or near-linear networks for reliable communication. LoRa is designed to be very resistant to interference [44]. Furthermore, the LoRa Channel Activity Detection (CAD) process enables a simpler, more-effective approach to contention management based on physical offsets rather than programmed delays [1]. We took advantage of this \"non-destructive communications\" characteristic of the LoRa physical layer to provide reliable communications in a LoRa-based linear network.  
LoRa is a spread spectrum technology that makes use of chirp spread spectrum modulation. A receiver will synchronise with a transmitter and, thereafter, expect communications at specific starting frequencies at the beginning of each symbol time. Transmissions outside those frequencies are ignored and treated as noise. This approach to the spread spectrum makes communications very robust, giving LoRa its impressive transmission distance, but it also makes possible a novel approach to dealing with contention in relay networks.  
Relay networks comprise a source, multiple relay nodes, and a destination. Contention is an issue in such networks where the recipient of a message (either the destination or another relay node) may receive the same message from multiple relays. Usually, concurrent reception of a message results in it being corrupted. Consequently, complex scheduling algorithms or strict limitations on transmission distance are usually necessary.  
However, because LoRa nodes synchronise with one transmitter and treat other transmissions as noise, LoRa makes it possible to avoid such complexity. So long as transmissions are not completely concurrent, two nodes transmitting the same message will result in the receiver synchronising with one transmitter and treating the other as noise. This is the \"non-destructive communications\" characteristic of LoRa. Furthermore, during the current transmission, a LoRa signal that traverses the shortest path will be treated as a wanted signal and other signals will be treated as interference. A preamble signal (depending on the LoRa configuration) is used to synchronise the receiver with an incoming data stream. The receiver captures the preamble symbols from the shared channel and tries to match them to the ideal waveform. Upon a successful match, it generates an interrupt to initiate the receiver process. We discussed the survival of LoRa during concurrent transmissions as presented in [1], which laid the foundation for this study.  
We show how this LoRa characteristic can be used to build simple and robust linear networks. We explored the situation with networks of different widths where a receiver can see one, two, or three nodes and demonstrate that a small physical offset of the nodes is sufficient to allow the receiver to synchronise with one of the relays and treat the others as noise.  
This characteristic of LoRa also means that simple networking routing becomes possible. Linear networks usually have simple routing requirements. We show that simple gossip routing provides high throughput with minimal complexity.  
We demonstrate how this characteristic can be used in managing contention and evaluated the performance of a number of networks of different thicknesses. We evaluated the performance of a LoRa-based linear network up to three hop counts by introducing the various thickness levels at each hop. Furthermore, we demonstrate the gossip-based approach by considering the various probabilistic distributions to reduce the traffic overhead and effective utilisation of radio resources.  
To the best of our knowledge, there is no empirical research as to the effectiveness of this approach for LoRa-based linear networks.