Choosing the right gateway on Join or Confirm

[julien-ioic]

Hi,

I created a small lorawan network with 3 gateways. Thanks a lot for this great job!! I see a recurent problem on the server response when the message are caught by multiple gateways.

How is done the choice between the severals gateways ? I think the better way is to select the gateway with the better SNR (the closest).

In the file join_request_accept.go.

line 190 : if err = ctx.Gateway.SendTXPacket(txPacket); err != nil { return fmt.Errorf("send tx packet (rx window 1) to gateway error: %s", err) }

Gateway is a unique object of the Context. I don't find where is referesh the context.

Thanks in advance,

Julien From Reunion Island ...

[yzk0281]

"How is done the choice between the severals gateways ? I think the better way is to select the gateway with the better SNR (the closest)."

Hi, Julien from the beautiful island, I think loraserver currently already handle this problem: in uplink_data.go call a func named collectAndCallOnce, and check this collectAndCallOnce in packet.go

‘ctx.Gateway’ is in loraserver/internal/loraserver/gateway/mqttpubsub/backend.go, it is initiated in loraserver/cmd/loraserver/main.go just check it there~~

[julien-ioic]

ok, I found it on loraserver/internal/loraserver/packet.go.

rxPackets implements the Sort Interface. using RSSI

func (p RXPackets) Less(i, j int) bool { return p[i].RXInfo.RSSI > p[j].RXInfo.RSSI }

In my log, SNR seems much accurate.

thanks.

[tftelkamp]

I'd agree that SNR is more relevant than RSSI.

However, SNR easily saturates for positive values, and then you don't see differences between the gateways: they're all good.

So maybe consider an algorithm like:

• select highest SNR
• if SNR > 5 then select highest RSSI from all gateways with SNR > 5

The threshold (5) we could tune.

[brocaar]

Thanks guys for your input! I won't fix this directly, as I'd love to get #68 out asap (it will involve a lot of code changes + changes in the api), but when it is better to use the SNR (combined with RSSI) instead of just RSSI, then I'm more than happy to change is :-)

[brocaar]

@tftelkamp @julien-ioic so then the sorting becomes something like:

func (s RXInfoSet) Less(i, j int) bool {
    // in case SNR is equal
    if s[i].LoRaSNR == s[j].LoRaSNR {
        return s[i].RSSI > s[j].RSSI
    }

    // in case the SNR > maxSNRForSort
    if s[i].LoRaSNR > maxSNRForSort && s[j].LoRaSNR > maxSNRForSort {
        return s[i].RSSI > s[j].RSSI
    }

    return s[i].LoRaSNR > s[j].LoRaSNR
}

Where maxSNRForSort=5.0 for now.

[brocaar]

Please see https://github.com/brocaar/loraserver/pull/88/files#diff-66307ebee4b6e63f8bc96622a5b96ccd. Looking forward to your feedback so I can merge it and put it in the next release :-)

[brocaar]

This has been implemented in the 0.12.2 release. Looking forward to your feedback! Thanks again for your feedback :-)

[julien-ioic]

hi,

sorry for the delay. It seems to be perfect. I'll check it soonly.

thanks a lot