C07 as LoRaWAN base station

Introduction

LoRa is a protocol for sending long-distance data packets (LOng RAnge). This is mainly used for packets with little information or a low frequency. This is approximately in the order of 10-15 data points every 5 to 10 minutes. In ideal conditions, such as an open space, good antennas and direct line of sight, the distance to be covered can be up to several kilometers. However, obstacles between the sensor and gateway negatively affect these signals. Metal constructions in particular can cause poor reception.

The use of LoRa sensors always requires a base station, in our solutions this is a Calculus C07W with built-in LoRa concentrator. It is best to place it as centrally as possible to ensure good coverage. The height of the antenna is also important here. The higher the antenna is placed, the better. Obstacles in the vicinity of the antenna should also be avoided. So if possible, do not place it flat against a metal wall, but try to stay away from it.

In the case of installations, you can also further optimise the installation based on a few values in the portal.

With LoRa, you also have the risk of packet loss. Up to 10% of packages can get lost. Confirmation may also be requested for crucial messages, but this is not recommended to do this continuously. This is because you get more radio traffic, making it more difficult for the other sensors to send their messages. If their confirmations fail, they are sent again, causing more and more radio traffic.

RSSI

RSSI, or Received Signal Strength Indication is the received strength of the signal. In short, this means how loud you hear a signal from the transmitter. This number is always negative and is usually between -120dBm and -30dBm. -120dBm is very weak reception, -30dBm is very strong reception. A sensor that sends messages at -120dBm also means that in worse conditions, more packets may be lost.

SNR

SNR, or Signal-to-Noise ratio, is the ratio of background noise to the transmitted signal. This value fluctuates between -20dBm and +10dBm. Again, the higher the value, the better.

SF

SF or Spreading Factor is a value that occurs specifically in LoRa, as opposed to RSSI and SNR, which are both values that are common in radio communication. Spreading Factor is a value between 7 & 12.

This is a setting that automatically adjusts itself based on the circumstances and the reception. As a comparison, you can see it as a value that says how fast you speak. The better the reception, the faster you can communicate and still be clearly understood. If the reception and distance is a bit greater, it is better to do this more clearly and slower. If a predefined number of messages is not acknowledged by the gateway, the sensor will go up a value on its own. SF12 is clearer here than SF7. However, longer steering also means more battery consumption.

With Elsys sensors, for example, this results in the following consumption:

As you can see, consumption is going up exponentially, so it is important to keep the Spreading Factor as low as possible. This can be done by a better location or placement of sensors and/or antenna.

Antenna placement

A LoRa antenna is not a directional antenna. These antennas work best by mounting them perpendicularly.

The ideal scenario is of course direct line of sight, but this is rarely possible in practice. Even with direct line of sight, but just above the ground you also have interference from the ground due to the fresnel zone. This is approximately an ellipsoid around the line of sight. You can calculate the exact size, but the most important thing is to realize that objects that are near the line of sight can also have an influence, and that placement close to the earth also causes interference.