To conclude this chapter, I would like to discuss a little bit about energy consumption. 1
Obviously, the energy consumption is directly linked to the autonomy of the device, and we need to 2
understand which parameter influence its value. 3
The main parameter is the Time On Air, 4
so the time used by the transceiver to send data. The Higher the Time On Air the higher consumption. 5
And the Time On Air is directly linked to the Spreading Factor. 6
As we already said, the higher the Spreading Factor the higher the symbol time. 7
So the higher the Time On Air. 8
Then the number of data to transmit and finally the bandwidth and coding rate. 9
Another element that will influence consumption is the fact that it can be collisions. 10
What happened when they are collisions? 11
Actually, nothing if you don't ask for an acknowledgement. And in that case the frame is just lost. 12
But if you ask for a confirmation, 13
so the protocol will spend time to confirm or retransmit in case of a packet loss. 14
And all this transmission will consume energy. 15
Then, there is a duty cycle parameter. 16
1% is the maximum. 17
But obviously there are many use cases where only a few LoRaWAN packets a day are enough. 18
And then you can save power. 19
Next of course, there will be the transmitted power. 20
In Europe, the limit is 14 dBm, which correspond to 25 milliwatts. 21
But of course, if you close to a gateway, there is no need to send this much power. 22
And finally, what does a LoRaWAN device do between two transmission ? 23
Usually nothing. 24
And the LoRaWAN transceiver and the application MCU (Microprocessor Unit). 25
should reach the deepest sleep mode to reduce the power as much as possible. 26
So to illustrate the power consumption point, we can just play with a little online calculator to get an idea of the autonomy we can expect. 27
In this calculator, we have to enter a few parameters. 28
I will keep my temperature sensor with one byte and assume that I need to send my data every one hour. 29
Finally, I will use a well known AA-type battery. 30
When we look at the results, the Time On Air generated are the one we had for LoRaWAN transmission. 31
For a LoRaWAN transmission, we need to had the LoRaWAN Header, which is 13 bytes. 32
So there are actually 14 bytes in the LoRa frame. 33
So I just change this value and I've got now the right Time On Air. 34
And the calculation gives the following result in the worst case will have 4 years and 11 months 35
for autonomy. 36
And in the best case, 17 years and two months, which is huge. 37
What does these figures actually represent? 38
They represent the consumption of the LoRa module. 39
We should also add the consumption that is linked to the application. 40
For example, if you're processing data for a long time, obviously if you have many sensors and so on. 41
Because they haven't been taken into account in this simulation. Then what's the worst case ? 42
The worst case would be a high Spreading Factor and a high transmission power. 43
Obviously, the best case would be exactly the contrary. 44
So a low Spreading Factor and a low transmission power, well, this still gives you a rough idea, 45
so just play along with it. 46
Change the parameters and try to see what's the autonomy you can expect for a LoRaWAN device.