LoRa as a Mesh Networking Technology

Although LoRa is primarily known for the long distances it can cover it also has characteristics that make it attractive as a relay technology in mesh networks. Unlike other wireless network technologies where concurrent transmission by two or more nodes results in corruption of both messages at the receiver, a LoRa receiver synchronises with just one transmitter and treats any other concurrent transmission as noise. This greatly simplifies the design of network relays in that they do not need complex schemes to deal with contention. It also reduces the number of copies of a message received at the destination. This approach also reduces latency when compared with schemes such as CSMA/CA used in other networks. However, there is a cost in terms of reduced Signal to Noise Ratio (SNR) which has a consequent impact on message error rate at the receiver. In this paper we use a two hop LoRa network comprising a transmitter, multiple relays and a receiver to evaluate the impact of concurrent transmission on latency, the number of packets forwarded, the SNR, the Received Signal Strength Indicator (RSSI) and the error rate as the number of relays forwarding a copy of the same message is increased. We observed that LoRa receivers synchronise with just one transmitter and forward only one copy of a message. We also observed that there is negligible latency regardless of the number of relays at each hop. However, we see an impact on SNR and successful message delivery. SNR reduces as the number of relays transmitting concurrently increases and successful frame delivery deteriorates rapidly once more than four relays forward a message with $\mathbf{4 5 \%}$ messages lost when there are seven relays.