Let's recap what's important for us. 1
We understood that the received power needs to be higher than the sensitivity for successful transmission. 2
Let's have a look at two cases. 3
In the first case we'll consider a transmission power of 0 dBm and we'll consider a sensitivity of -100 dBm. 4
In this case, between the transmitted power and the sensitivity, 5
we have a difference of 100 dB and this 100 dB is our budget. 6
This means that it's what we are allowed to lose in the air, in the connectors and cables and all the 7
way along a transmission path. 8
Now, let's take a second case: with a transmitted power of -20 dBm, and we now consider the sensitivity 9
of the receiver of -120 dBm. 10
The difference between the two is still 100 dBm. 11
Which transmission is more interesting? 12
In fact, they are exactly the same because under one hand you have the higher transmitted power but 13
a bad sensitivity, and in the second case you have a lower transmitted power, but also a better sensitivity. 14
Let's make an analogy of what we just said. 15
We can consider that the transmitter and the receiver are on the one hand as speaker and on the other 16
hand a listener. 17
In the first case, the speaker use a loud voice with someone who doesn't hear very well. 18
And in the second case, the speaker whispered to someone who has a very good hearing, and at the end 19
of the day, it's all about your budget. 20
So only the difference between the transmitted power and the sensitivity matters. 21
And again, this difference is called link budget. 22
There is one thing interesting in the 23
second case though, it's that the transmitted 24
power is lower, so it consumes less. In 4G transmission 25
the budget available is around 130 dB. 26
In LoRa, we have a budget of 157 dB and that result of a longer transmission distance. In LoRa, the 27
world record of a transmission between a transmitter and a receiver was broken in april 2020 and it's 28
832 kilometers. 29
They of course complied with the European standars with a maximum transmission power of 15 dBm, which 30
corresponds to 25 mW. 31
This is, of course, something realized in a very specific conditions, and you will never reach this 32
level of performance in the field. 33
So now let's have a look at an example to recap everything.