The first two bitrates we found, depending on two parameters, the spreading factor and a bandwidth. 1
These two parameters are those we will have to configure in the Lora device to make it work. Actually, there is an additional 2
that is more parameters that will influence the bitrate. 3
And this additional parameter is what we call the coding rate. 4
So what is it and how does it really influence the bitrate? 5
The coding rate says that if, for example, we choose the value 4/5, then each time we 6
transmit 4 bits, then in a reality we'll transmit 5. 7
If we take a coding rate of 4/8, then each time we transmit 4 bits, we will in reality 8
transmit 8. 9
What's the purpose of that? 10
Because here we have the impression that we are just adding bits, but in fact these additional bits 11
would improve the robustness of the communication. 12
Why is that? 13
Because these additional bits will be able to detect and possibly even correct error. 14
That's the good part. 15
But a bad one is that these additional elements will produce what we call an overhead ratio. 16
This means that they will increase the number of bits without increasing the useful information, and 17
so the useful bit for the user will be deteriorated. 18
Let's take the two cases we've seen so far. 19
First at SF7, with 125 kilohertz bandwidth and with the coding rate of 4/5. 20
If I choose 4/5 coding rates, it's because it's the most commonly used. 21
But we must keep in mind that it's not the worst case. 22
On a second case, we'll be at SF12 with the same bandwidth and the same coding rate 4/5 23
. 24
This time we have a deterioration of the data rate, which obviously correspond to the overhead ratio. 25
And if we do the calculation, that's 6 836 kbps divided by a ratio of 1.25, and we find 26
5469 bits per second. 27
For software, we find 293 bits per second, which has significantly reduced its initial value.