Application of 915 MHz Band LoRa for Agro-Informatics

Use of the LoRa low-power wide-area network modulation scheme with the LoRaWAN® (Long Range Wide Area Network) MAC layer is becoming popular for subterranean agro-informatics networking applications. LoRa uses chirp spread spectrum technology and is licensed by Semtech. Sensors with LoRa radios can be designed to detect and measure toxins that can leach into agricultural soils from industrial and storm water sources. Sensors can be buried with cameras that can detect and classify pathogens affecting the roots of plants. Sensor measurements and camera images can be sampled in situ and transmitted to an above-ground central LoRa concentrator (gateway) on a farm. LoRa devices can be buried at variable depth, however soil and water both attenuate the strength of a transmitted signal. In this work, we conduct experiments to measure the received signal strength indicator (RSSI) and signal-to-noise ratio (SNR) under different LoRa spreading factors, coding rates, and soil depths. Our results show LoRa transceiver burial depth should not exceed 50cm for agro-informatics applications.