On the Lorawan infrastructure, 1
we've already explained the network and application server. On the previous video, 2
we've also worked on gateways. 3
Now we will focus on the end device itself. 4
On the end device, there are two kinds of frames. 5
The ones that go to the gateway and network server, that's what we call the uplink frames. And the ones that 6
come from the network server then gateways 7
and finally reach the end device. 8
That's what we call downlink frames. 9
So let's see how the communication is handled from the end device side. 10
We remind that when the end device want to transmit, it will power up its radio and send a packet. 11
The packet transmission time is what we call the time on air. 12
And then after a certain time, it will be able to transmit a new message. 13
In Europe, it has to be in respect with the 1% duty cycle. 14
On this diagram, we can't see how to downlink is carried out. 15
In other words, when it's the right time for the gateway to transmit the packet coming from the server. 16
Actually, to understand when downlink frame can be transmitted, 17
we need to introduce the end device classes and we have to know that there are three classes A, B or 18
C. 19
So for the class A end device, its downlink capabilities are very limited. 20
The class A end device is the one that want to use the less power as possible. 21
So most of the time it want to stay in low power mode. 22
The problem is that while a device is in low power mode then it can't receive. 23
So the only opportunity that the end device offers to receive a packet from the network is to open 2 small 24
time slot that we call RX1 and RX2. They occur right after each uplink. 25
The default value of RX1 and RX2 are 1 second and 2 seconds. 26
But for solving network latency issue in certain situation, it's often set to 5 and 6 seconds. 27
That's the network server that decides delays and obviously it has to be the same on the end device 28
and on the network server. 29
Finally, what will the device do outside of this timeslot? 30
Of course, go to low power mode. 31
So I want to highlight a very important feature of class A end device. It is able to receive only if it has transmitted 32
so that make a very few downlink opportunities. 33
But on the other hand, it has a low power consumption. 34
Can we improve the drownlink capability? 35
Of course, yes. 36
By using a class B, the class B as exactly the same behavior in place A, except that there are other 37
timeslot between uplinks. 38
But a setup is a bit tricky because end device up to be perfectly synchronized with the gateway. 39
So periodically there are time beacons that are emitted by the gateway to synchronize Lorawan end 40
device. 41
And another thing is that we can configure the time between each timeslot, so you can configure the 42
downlink opportunities for the network. 43
Again, what we on device do outside of this timeslot of course go to low power mode. 44
So finally, if we compare the Class B with the Class A, then class B has more possiblity to receive 45
a lorawan message from the network. 46
But obviously because it opens more reception windows and it will consume more power. Can we again 47
improve the downlink capability? 48
Yes. 49
And this time by using a class C end device, the Class C has exactly the same behavior of Class A. But, 50
when the end device is not transmitting or receiving on the classic RX1 or RX2 timeslot, then it keeps 51
the radio on. 52
So the end device is always able to receive between two uplinks. 53
Of course there is a huge consequence on the power consumption. 54
So we can summarize these three classes with this little diagram, and for each of them we want to know 55
on the one hand and downing capability and on the other hand, the power consumption. Class A is definitely 56
the one that has the best power consumption performances. 57
On the other hand, you can reach device only if it has transmitted. 58
Class B allows to add a reception slot. 59
This means that we will have more chances to send Lorawan messages from the network. 60
And finally, the Class C can be reached at any time except when it's transmitting. 61
But obviously the consequence is that it consumes a lot of power. 62
So on a battery powered device, what can be done is that we leave as much as we can Lorawan end device 63
in a class A and as an end device doesn't have to sit all is life in a specific class. 64
Then we can switch from class A to B or from A to C only when it's necessary. 65
Now. 66
When we look back at the entire Lorawan network, what do we need to be sure for the transmission 67
to be successful? 68
Every part of the network has to support the class you want to use. For class A, 69
No worries. 70
Everyone supports it. For the others, 71
We have to make sure that the end device, the Gateway and the networks server have provide this service. 72
And that statement applies especially for Class B, because you will need a specific gateway able to 73
provide an absolute timestamp that is often made thanks to G.P.S. So now we'll give a demonstration 74
of this classes on the Lorawan network.