Uplink shows duplicate gateways in metadata, with different values for channel, RSSI and SNR (and sometimes timestamp)

Application Development
1

We have a device (from Elsys) working and transmitting data periodically. It is being received by a number of gateways, but we are seeing duplicate metadata when we inspect the individual packets … and moreover whilst the gateway ID is the same, some of the actual metadata is different … does anyone know what is going on?

If I look at an individual received packet in the TTN Console … e.g. Applications -> elsys-elt2-mb7389-ttn -> Data

I’ll see …

image

Clicking on the up-triangle there lets me see the detailed data and meta-data, and the latter shows me which gateways received the packet.

You don’t need to read this, but it looks like this …

image

Here is the actual metadata, hopefully legible this time …

{
  "time": "2020-04-14T19:38:00.87002551Z",
  "frequency": 867.7,
  "modulation": "LORA",
  "data_rate": "SF12BW125",
  "coding_rate": "4/5",
  "gateways": [
    {
      "gtw_id": "eui-a840411d1f0c4150",
      "timestamp": 1390247508,
      "time": "2020-04-14T19:38:00.847405Z",
      "channel": 6,
      "rssi": -49,
      "snr": 9.2
    },
    {
      "gtw_id": "eui-b827ebfffec0c17b",
      "timestamp": 4287703196,
      "time": "2020-04-14T19:37:59.816229Z",
      "channel": 6,
      "rssi": -41,
      "snr": 9.5,
      "latitude": 51.45733,
      "longitude": -0.21949,
      "altitude": 55
    },
    {
      "gtw_id": "eui-b827ebfffebbe35f",
      "timestamp": 2679433092,
      "time": "2020-04-14T19:38:00.849584Z",
      "channel": 6,
      "rssi": -54,
      "snr": 11,
      "latitude": 51.45725,
      "longitude": -0.21874,
      "altitude": 27
    },
    {
      "gtw_id": "eui-b827ebfffe5852a9",
      "timestamp": 4167918644,
      "time": "2020-04-14T19:38:00.85149Z",
      "channel": 5,
      "rssi": -89,
      "snr": -15.2,
      "latitude": 51.45731,
      "longitude": -0.2191,
      "altitude": 30
    },
    {
      "gtw_id": "eui-b827ebfffe5852a9",
      "timestamp": 4167918644,
      "time": "2020-04-14T19:38:00.85149Z",
      "channel": 6,
      "rssi": -46,
      "snr": 10.2,
      "latitude": 51.45731,
      "longitude": -0.2191,
      "altitude": 30
    },
    {
      "gtw_id": "eui-a840411b7c544150",
      "timestamp": 4196549252,
      "time": "2020-04-14T19:38:00.86441Z",
      "channel": 6,
      "rssi": -64,
      "snr": 10.8
    },
    {
      "gtw_id": "eui-60c5a8fffe74d31e",
      "timestamp": 369925268,
      "time": "",
      "channel": 6,
      "rssi": -47,
      "snr": 10.8,
      "latitude": 51.45725,
      "longitude": -0.21874,
      "altitude": 34
    },
    {
      "gtw_id": "eui-b827ebfffe45866e",
      "timestamp": 3541415508,
      "time": "2020-04-14T19:38:00.873465Z",
      "channel": 6,
      "rssi": -59,
      "snr": 9.5
    },
    {
      "gtw_id": "eui-b827ebfffe45866e",
      "timestamp": 3541415532,
      "time": "2020-04-14T19:38:00.873465Z",
      "channel": 5,
      "rssi": -90,
      "snr": -8.8
    },
    {
      "gtw_id": "eui-58a0cbfffe800555",
      "timestamp": 499739100,
      "time": "2020-04-14T19:38:00.860600948Z",
      "channel": 0,
      "rssi": -49,
      "snr": 10.25
    },
    {
      "gtw_id": "sentriusrg186-putneyhill",
      "gtw_trusted": true,
      "timestamp": 49116660,
      "time": "",
      "channel": 6,
      "rssi": -47,
      "snr": 9.5,
      "latitude": 51.457245,
      "longitude": -0.21874009,
      "altitude": 30
    },
    {
      "gtw_id": "eui-3232393456005e00",
      "timestamp": 3262074252,
      "time": "",
      "channel": 6,
      "rssi": -37,
      "snr": 7.3
    },
    {
      "gtw_id": "ttngateway-putneyhill-londonsw15",
      "gtw_trusted": true,
      "timestamp": 348184516,
      "time": "2020-04-14T19:37:55Z",
      "channel": 6,
      "rssi": -47,
      "snr": 10.25,
      "latitude": 51.457245,
      "longitude": -0.21928726,
      "altitude": 30,
      "location_source": "registry"
    },
    {
      "gtw_id": "ttn-001-868-new",
      "gtw_trusted": true,
      "timestamp": 1473319940,
      "time": "2020-04-14T19:38:07Z",
      "channel": 6,
      "rssi": -49,
      "snr": 9.5
    }
  ]
}

The gateways eui-b827ebfffe5852a9 and eui-b827ebfffe45866e appear twice …

First instance …

{
  "gtw_id": "eui-b827ebfffe5852a9",
  "timestamp": 4167918644,
  "time": "2020-04-14T19:38:00.85149Z",
  "channel": 5,
  "rssi": -89,
  "snr": -15.2,
  "latitude": 51.45731,
  "longitude": -0.2191,
  "altitude": 30
},

Second instance …

{
  "gtw_id": "eui-b827ebfffe5852a9",
  "timestamp": 4167918644,
  "time": "2020-04-14T19:38:00.85149Z",
  "channel": 6,
  "rssi": -46,
  "snr": 10.2,
  "latitude": 51.45731,
  "longitude": -0.2191,
  "altitude": 30
},

So, same gtw_id and timestamp, but different values for channel, rssi and snr.

Likewise:

{
  "gtw_id": "eui-b827ebfffe45866e",
  "timestamp": 3541415508,
  "time": "2020-04-14T19:38:00.873465Z",
  "channel": 6,
  "rssi": -59,
  "snr": 9.5
},

and:

{
  "gtw_id": "eui-b827ebfffe45866e",
  "timestamp": 3541415532,
  "time": "2020-04-14T19:38:00.873465Z",
  "channel": 5,
  "rssi": -90,
  "snr": -8.8
},

Again the same gtw_id and different values for channel, rssi and snr, and also different timestamps.

2

Are it always the same two gateways that are listed multiple times?

An earlier case was caused by a gateway really reporting the same uplink multiple times, caused by some bad soldering on the antenna connector: Single message shown multiple times with different channels, SNR and RSSI in rxpk of IC880a gateway log.

Also, any chance your device is very close to these two gateways?

2 Likes
3

Yes! This is a test scenario actually, with multiple gateways fairly close (5m) to the the sensor. So that is the problem, probably – crosstalk??

Is there a well understood minimum distance defined anywhere?

Thanks so much for the help!

1 Like
4

On some gateways like Multitech Conduit you get that a message is received on two frequencies when you overload the frontend. In other words when you are very close to the gateway. This is your case. It’s clear from the RSSI values.

2 Likes
5

Thanks so much. I just am not very RF savvy … so this was not even in my consideration set!