Gateway Sx1302 reboot unexpectedly when Tx downlink RX2 869.525MHz

[ubs_irisa_casa_ttn]

Hi everyone,

I am working with my gateway Waveshare SX1302_HAL, STM32WLE5 end-device, TTS Sandbox. The gateway library is GitHub - Lora-net/sx1302_hal: SX1302/SX1303 Hardware Abstraction Layer and Tools (packet forwarder...). The uplink and downlink RX1 work fine. However, when trying to send downlink RX2 in freq 869.525MHz, the gateway reboots itself unexpectedly. This downlink eventually still reaches the end-node but the packet forwarder does not work anymore.

Can you help me with this issue?
Thanks in advance.

[Jeff-UK]

Mre info and investigation likely neccessary…

Which platform are you using it with? A Pi? Which model?

Where you say

@ubs_irisa_casa_ttn

The uplink and downlink RX1 work fine.

Have you tried with all SF’s? and long payloads?

If you are testing and close likely node running SF7/8?

My initial suspicion would be a PSU issue especially if using are e.g. later/higher powered Pi and with marginal supply.

Tx sucks juice and a long payload (what is the SF9 RX2 downlink payload?) may be just enough to tip over the edge as SF9 ~2-4x ToA c/w lower SF’s and PSU may be sagging, esp if Txing at full power.

Try better PSU, test all SF’s for RX1 and push to limits to see if repeatable…

[kersing (Jac Kersing)]

@ubs_irisa_casa_ttn

the gateway reboots itself unexpectedly

Does the gateway reset? Or does the packet forwarder crash? In the first case I agree with @Jeff-UK and my first suspect would be a power issue.

[ubs_irisa_casa_ttn]

For more information, my gateway is based on Raspberry Pi 40 pin.
@kersing Pi reboots, not the packet forwarder.

I am doing more test on that.

[kersing (Jac Kersing)]

@ubs_irisa_casa_ttn

Pi reboots

Points to power issue. If you connect a display to the RPi do you see a warning? (Dealing with the Low Voltage Warning on the Raspberry Pi - Pi My Life Up)

[ubs_irisa_casa_ttn]

Many thanks to @Jeff-UK @kersing.
It’s true that the problem comes from power supply. In the global_conf.json file, I reduced the maximum value of rf_power from 27 to 24. It means that even though the packet sent from TTN with power 27dbm, the gateway finally transmits it to end nodes with 24dbm. It works fine for now. But the problem might be raised in the future.
To be sure, I have some question:

1. How TTN decides the power of a downlink pkt?
2. Is there any way for my gateway (or Raspberry) can suffer higher power (even more than 27 dbm)?

[descartes (Nick McCloud)]

@ubs_irisa_casa_ttn

How TTN decides the power of a downlink pkt

That’s all in the documentation - but basically full power unless it’s at SF7 and then it will dial down.

@ubs_irisa_casa_ttn

is there any way for my gateway (or Raspberry) can suffer higher power

If you like prison food, sure, put a bigger supply on, directly to the board. In the meanwhile, perhaps dial back the output to the EU legal limits.

[Jeff-UK]

@ubs_irisa_casa_ttn

I reduced the maximum value of rf_power from 27 to 24

Try 16! (If you dont want legal trouble for yourself or your french Uni.)

[ubs_irisa_casa_ttn]

Thanks all !

[wolfp (Wolfgang)]

imho 27dBm is legal at 869.525MHz in EU. Nevertheless this is much to much output-power.

[descartes (Nick McCloud)]

But has the OP set it globally or just for that channel / frequency?

[kersing (Jac Kersing)]

You can’t set it for a specific frequency. Just update the global lookup table that is used to translate the LNS settings to the gateway specific hardware.

[descartes (Nick McCloud)]

So in terms of LoRaWAN, for anyone coming at this from a Google search, the potential higher output on 869.525 is somewhat academic.

Particularly if combined with the imbalance in the send / receive power - a gateway with a good antenna may hear a device right at the limit of the devices capabilities, facilitate a join because it can boom out the join accept, but on a typical day, the device isn’t being heard.