This post is a VLOG entry, as usual in French, you will find the english text version in the next part of the post.
Basically, I’m explaining how the two LPWAN technologies : Sigfox and LoRa use the radio frequency to communicate with a low power consumption in a wide area environment.
In this video you will find a mix of demonstration with voice to highlight how it works with day-to-day life example and spectrum capture of both technology to visualize how it looks like.
These two technologies are based on different approach :
- Sigfox use UNB – Ultra narrow band, it means the available transmission power is applied on a really small bandwidth (100Hz). This is looking like whistling to be hear from a long distance and cover the environmental noises.
This can be represented by the following FFT : the first one is a environment with music and the voice is difficult to hear in the environment because its signal have less power than noise. The voice energy is spread over multiple low frequencies:
This second picture show the energy of a whistle creating a spike at a precise frequency.
If we now take a look to a real Sigfox transmission, we can see 3 consecutive spikes corresponding to the 3 emissions of the same message on different Sigfox channels. We see the energy spike really concentrated to a really small bandwidth, exactly like when whistling as demonstrate previously
- Lora use spread spectrum the communication is based on the use of multiple frequency to send the same part of the message multiple time. This allow to transfer a message even if a part of the signal is jammed by another transmission or by environmental noise. The impact on the bandwidth is totally different as illustrated in this capture :
For the duration of a sigfox transmission you see much more bandwidth use for the transmission : each of the message bit is transmitted on multiple frequencies. The message is transmitted only once if you accept message loss.
As the transmission speed can be changed by reducing the spreading factor, in higher rate the signal will be as larger but its duration will be really shorter in the water-fall.
It is interesting to see what is happening when these two technologies are communicating together :
We see in this screen capture the Sigfox communication clearly visible on top of the LoRa communication (the orange-red line in the bottom) We can assume we still have enough signal to extract the message. More over the last transmission is clearly not impacted by the communication. LoRa transmission is really large and thanks to the message redundancy we are quite sure the message can also be decoded.