Measurement of 868MHz LoRa radio propagation in a tunnel

In this article the measurement method and results for a measurement with LoRa in a tunnel is shown, using a custom LoRaWAN Data-Logger and DR 0, in the LoRaWAN EU868 region at 868 MHz. After an initial attenuation of 66 dB for the Data-Logger and 49 dB for the Gateway, an attenuation of 14 dB/km for the RSSI of the Data-Logger and 17 dB/km for the RSSI of the Gateway was obtained. For this results the Data-Logger and Gateway were placed in the middle of the tunnel cross-section in a height of 1.7 m. If the Data-Logger was placed in one of the five diagonal transverse the signal degraded quickly by up to 40 dB. Additional tests with different positions of the Gateway and the Data-Logger in the cross-section of the tunnel showed the significant influence of placement in the cross-section. For all situations the suitability of LoRa in tunnels is shown. The tunnel had a usable length of 2400 m, a width of 8 m, and a rounded ceiling at 6 m. The walls and ceiling were a combination of natural stones and sprayed concrete, the floor was tarred. No active traffic was in the tunnel during measurement. The measured RSSI and the SNR values showed that the whole tunnel could be covered with a single LoRa Gateway at the tunnel portal