ADR for low snr seems to not be working

ChirpStack Network Server
1

Hi there

Using AU915_928 Band RX1 = 5 and RX2 = 6.
We have a device which was very near the gateway.

  "rssi": -77,
  "loRaSNR": 10,

At that time it was using DR=6 as expected.

Now we moved the device 300 meters far from gateway.

  "rssi": -112,
  "loRaSNR": -9.2,

The ADR still on 6:

  "txInfo": {
    "frequency": 915900000,
    "dr": 6
  },

Here is the mac_command sent to the device after the uplink:

{
    "downlinkMetaData": {
        "gatewayID": "XXXXXXXXXXXXX",
        "txInfo": {
            "frequency": 923300000,
            "power": 27,
            "modulation": "LORA",
            "loRaModulationInfo": {
                "bandwidth": 500,
                "spreadingFactor": 7,
                "codeRate": "4/5",
                "polarizationInversion": true
            },
            "board": 0,
            "antenna": 0,
            "timing": "DELAY",
            "delayTimingInfo": {
                "delay": "5s"
            },
            "context": "5XqxAQ=="
        }
    },
    "phyPayload": {
        "mhdr": {
            "mType": "UnconfirmedDataDown",
            "major": "LoRaWANR1"
        },
        "macPayload": {
            "fhdr": {
                "devAddr": "00021011",
                "fCtrl": {
                    "adr": true,
                    "adrAckReq": false,
                    "ack": false,
                    "fPending": false,
                    "classB": false
                },
                "fCnt": 1228,
                "fOpts": [
                    {
                        "cid": "LinkADRReq",
                        "payload": {
                            "dataRate": 6,
                            "txPower": 11,
                            "chMask": [
                                true,
                                true,
                                true,
                                true,
                                true,
                                true,
                                true,
                                true,
                                false,
                                false,
                                false,
                                false,
                                false,
                                false,
                                false,
                                false
                            ],
                            "redundancy": {
                                "chMaskCntl": 0,
                                "nbRep": 3
                            }
                        }
                    }
                ]
            },
            "fPort": null,
            "frmPayload": null
        },
        "mic": "ca3f664c"
    }
}

It keeps sending DR = 6.
With the SNR like that, very poor quality, it should use DR around 3. No ?

Maybe I’m missing something on config or my understanding ?
Thanks

2

The NS does not lower the data-rate, it will only increase the DR. If the device becomes “disconnected” while using ADR, then it will start using the ADR backoff algorithm. Please see the LoRaWAN specs. for more information on this topic.