For some time, I have been launching ultralight (4 grams) LoRaWAN enabled payloads on floating balloons. These balloons fly for a couple of days, weeks or even months travelling many thousand km.
For the newest probes, I have heavily optimized not only the hardware, but also software. I’ve added many safety features for more stable power usage and geofencing. I’ve been researching the Limitations and the Fair Access Policy for quite some time now. The thing is, until now I transmitted messages with these parameters:
Payload size: 5-10 bytes (new payload packets will be around 20 bytes though)
Spreading Factor: SF12
Transmit power: 20dBm
Delay between messages: 10 minutes (though the probe is over land for not very long so there can be only 5 or so messages in a day)
I was launching the balloons from central Europe and none of them got further than to eastern Europe. I got a range of around 400km (judging from the distance between the gateways that were the furthest apart and received the message at the same time). The messages were received by more than 20 gateways in central Europe but only by 1 gateway when flying over western Europe.
Only later I found out that hardcoded SF11/SF12 is forbidden. The problem is, when using SF10, I risk that no gateway will actually receive the message because it is out of range. From what I’ve read, this is not enforced on a global (network provider scale) but can be enforced by the owner of the gateway. How can I deal with this? Can I transmit half of the messages on SF9/SF10 and the second half on SF11/SF12? Also, since the probe is travelling at 150km/h and also is rotating with its directional antenna, almost every other message is received by a different gateway. This means that I’m not “polluting” the same local network. Does that change the fairness of the transmission?
Also, even though my previous probes never left the EU868 band, it’s very probable that the new probes will go much further. Because of this, I’m implementing geofencing to switch the frequency band during flight. But, I found out that for example on the US915 band, it’s not possible to use a spreading factor of more than SF10 because of the maximum dwell time. Will the probe not work at all in this area? Should I just switch to SF10 automatically when switching to that frequency band?
One more thing. How does the airtime actually affect the range of the transmitter? Let’s say I have an airtime of 1812ms on SF12 and an airtime of 452ms on SF10. How much smaller should I expect the range to be? 30%? 40%? 50%? I know that’s impossible to predict precisely, I just want an estimate.
I had a lot of questions here, so thanks a lot in advance to anyone who knows the answer.