In view of a usage in long distance sensor networks, AURORAS has tested the range of transmission of modules with technology LoRa.
The test took place in the open field using two modules, one configured as a transmitter and the other as a receiver connected via serial port to a laptop.
The test provided for the monitoring of two main parameters:
1. SNR (signal to noise ratio)
2. RSSI (strength indicator of received signal)
The configuration of the two nodes has been the following
- Channel: CH_14_868
The LoRa technology provides for the possibility, in the European version, at 868 Mhz, to choose between 8 different channels. - Power: High
Regards the transmission power that can be configured in 3 different modes: Low, High, Max
LOW 0dBm
HIGH 5dBm
MAX 14dBm
The first step was to identify the transmission point. It was chosen a light pole of sports field with the purpose of heightening the transmitter of approximately 15 meters from the ground.
In the image we can observe the positioning of the transmitting node.
Once this has been installed, it proceeded to the verification of the receipt of the signal ground, about 15 meters away.
The result was as follows:
SNR: 7
RSSI: -114
Maintaining the same settings we proceeded to move about 7 km in a straight line. The orange circle indicates where it was located, roughly, the receiving node. The two nodes didn’t see each other physically. The receiver has been placed on the plain with the presence of natural obstacles (trees) which effectively took away the “line of sight”
The modules had no problem receiving. The transmission, lasting about 30 minutes, it did not suffer any loss of data.
The transmission took place every two minutes.
The result was as follows:
SNR: -17
RSSI: -110
We note that for a RSSI virtually unchanged, the signal / noise ratio is greatly changed. This has not been a problem taking into account that the LoRa modules can manage a SNR up to -20dB
The third and final test was carried out by increasing the distance up to 10 Km. Place chosen to place the receiver: the hills of San Colombano al Lambro about 200 meters above sea level with the presence of natural obstacles such as trees. Also in this case we got a transmission without problems.
The result was as follows:
SNR: -16
RSSI: -110
We can see that SNR and RSSI have remained unchanged since the previous transmission thanks to of the fact that the receiver module was elevated by 200 mt.
Conclusions:
We can say that the test on the transmission range of LoRa modules made by us was positive giving us the security that this technology is stable and ready for use in networks of long distance sensors.
