I have a 8 channel gateway which means i can receive 8 messages at the same time. What happens if I have 200 devices all sending at the same time to this 8 channel gateway ?
The 8 different uplink frequency channels are orthogonal to eachother (ie they will not interfere).
Within an uplink frequency channel the different SF levels are partially orthogonal, depending on power levels.
At the very most you would receive 8 channels x 6 SF levels (7…12) = 48 uplink messages. You would lose the other messages without trace unless they have requested an ACK.
In reality I think that you might receive 5 to 10 messages as the uplinks are unlikely to be be perfectly distributed across the frequency channels and SF levels.
Please give it a try and let the forum know how you get on.
That’s not true. There’s only 8 physical demodulators. Plus one for FSK and one for LoRa STD.
You’re correct. My mistake. Thanks.
In theory, you can receive 8 messages at once, on 8 different frequencies or perhaps including some which are on the same frequency but at different spreading factors.
The missing element then is that of time - to support 200 nodes, you rely on the fact that they aren’t all talking all the time. In fact, in a LoRaWAN network each node should be sending quite infrequently, for all of technical / battery / legal reasons, before even getting to questions such as the TTN fair use policy.
If you need to be constantly sending data at short intervals you cannot use TTN, and its questionable if you can use LoRa at all.
If you need nodes to optimally share the radio capacity in a non-random way, you need to use a protocol other than LoRaWAN.