Hi everyone,
I’m fairly new to LoRa and so far I’ve created an RN2483 shield for Teensy, RPi and USB as nodes.
I would like to setup a gateway and I’ve been looking at the iC880A, but one thing is uncertain to me. Is it possible to also send messages from this gateway? For example I would setup the node to send a message and then listen for one minute. The gateway should receive the message and if needed, send an instruction message back. Can the iC880A accomplish this or would I need to add an RN2483 to the gateway just for sending messages? Alternatively, is this why some gateways are so expensive, being able to Rx and Tx? Or is the price difference mainly in capacity?
RN2483 modules adhere to LoRaWAN class A. This means after a transmission they are able to receive data in the RX1 slot (currently 1 second after transmission) and RX2 slot (2 seconds after transmission). Listening for 1 minute is not possible with the current firmware.
The iC880A is able to send data to any node adhering to the LoRaWAN standard. Keep in mind a gateway can not receive data from any node while it is transmitting.
Thanks for the clarification. What distinguishes a class A device from class C? For example if I wanted to use the node to light an LED, I would need it to be listening most of the time.
On the staging docs there was this article called ‘Can we use LoraWan/The Things Network to control our lights’. The article isn’t online anymore, but the answer is still ‘no’. Not only is class C (node always listening) not supported right now, the gateway also must adhere to the duty cycle limit which is 1% airtime in TTN. You can find the exact calculation in several threads on this forum, but under normal situations this means you will be able to send around 10 downlink messages to your node per day. So if you are alright with only 10 switching commands per day you can use it, but otherwise you’re better of with different technologies.
Remember that LoraWan is not meant as a symmetrical communication method. Nodes communicate to the gateway and in certain situations the gateway can communicate to the node. But this last bit must be kept to a minimum.
Thanks for the info. I will read more on the wiki.
One thing that is uncertain to me is whether these rules apply when using the TTN network or if they’re built into the stack? Ie. if I make my own small network, do I still have to abide by these rules or would this require switching to FSK? I wouldn’t necessarily need symmetrical communication, but I may need a node that only listens, it would be the opposite - receive many more messages and send only sporadically.
If you want to use LoraWan (or any other technology in the ISM band afaik), you need to adhere to the max duty cycle of 1% per subband. Afaik TTN uses a 0.1% duty cycle to keep some headroom. This duty cycle also applies to the gateway, which is just another LoraWan participant.
1% airtime is still a lot tho. You could roll your own Lora network (not LoraWan) for P2P communication like this, and assuming a short message takes 20ms airtime you could send a message every 2s. In a private network you could also cycle subbands in order to gain more airtime, but if you really need to push the limits you’re better of with other technologies.