Efficient Image Transmission Using LoRa Technology In Agricultural Monitoring IoT Systems

Reliable image transmission using LoRa in IoT monitoring systems is considered to be challenging due to insufficient LoRa data rate and payload size. Existing approaches transmit an image in a sequence of packets each of which is individually acknowledged. This approach results in a long image transmission time due to the time spent waiting for the many individual acknowledgements. The acknowledgement traffic also inflates network load. To facilitate LoRa-based image transmission in agricultural monitoring IoT systems, this paper proposes a new reliable delivery protocol, Multi-Packet LoRa (MPLR), for transmission of large messages, such as images, in LoRa networks. The proposed protocol is implemented and evaluated using a LoRa testbed network. In point-to-point experiments with a single sender/receiver pair, MPLR reduced image transmission time by an average of 24% in scenarios with no packet loss, and by averages of 30%, 42%, and 49% in scenarios with 2%, 5%, and 10% loss rate, respectively. When multiple LoRa nodes send images to a single gateway, high channel utilization and an unacceptable collision probability can be experienced with the standard LoRa MAC ALOHA protocol. In experiments with between 5 and 20 nodes, MPLR in conjunction with a channel reservation protocol can successfully send more images and reduce the maximum successful image transmission time between 2 and 7 times, compared to stop-and-wait packet transmission with ALOHA.