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