Lopy4 + Pysense using LoRaWAN tracker

  • Hey guys,

    I'm doing a project for wildlife tracking with a lopy4 + pysense setup using LoRaWAN and TTN
    as server (low-cost) and i'm wondering (after researching about the subject) if it's possible to
    track positions in LoRaWAN using Time Difference on Arrival (TDoA).... I'm researching about tracking with
    RSSI which will give me lower accuracy than TDoA.

    However i can't seem to find any usefull information about TDoA I mean the method and theory is all pretty basic
    but i mean, real usefull information is hard to find for example:

    • Where could I find information about timestamps ?

    So can anyone tell me if its possible to use Lopy and lopy nano Gateways to use TDoA
    or is it only possible when you have some more sophisticated hardware on hands?

    Thank you

  • @morrison Never looked into the details, but using NTP sync with decent connections between the LoPy4 and the network should yield decent timekeeping. Make sure you have the exact time of arrival of a frame (including fractional seconds) in the data sent to the network, and if you know the exact position of your gateways you should be able to compute the location of the node.

    Of course as @aliubi stated the accuracy may be limited, not sure if that would useful to you with that kind of resolution.

  • @morrison You also don't have the bandwidth you'd really want to do TDoA. At 500KHz bandwidth, you've got on the order of 2us resolution, which is on the order of about 2000 feet. GDOP will cut into that fairly quickly, so best case with perfect timing you're going to have around 3000 feet (~1Km) resolution.

  • Yes i have three lopy4 nano-gateways but as i suspected
    I don't have GPS and I don't have high resolution timestamps

  • @morrison TDoA is a feature on the network side (gateways and LNS), as the time difference will be measured by the LNS based on timestamps from the gateways.

    For it to work, you need:

    • the gateways to have precise timekeeping (NTP or GPS)
    • the gateways to provide high resolution and consistent timestamps to the LNS (and possibly the application server)
    • the LNS or application server to know the precise position of the gateways (either in advance or via information sent by the gateways)

    So this mostly depends on the gateways. What gateways are you using? Do you actually have 3 or more gateways covering all areas?

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