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A-GPS Data Consumption

Hello,

What the average data consumption for using A-GPS on the nRF9160 to download the Almanac and Ephemeris data? I would like to know how much data is billed through my carrier for performing this operation.

Regards,

Akash Patel

  • Hi,

    Exactly how much data is used depends on the protocol used, the data available, etc.

    There was some numbers in the nRF91 Software roadmap from February:

    (with SUPL, if I understood the powerpoint correctly):

    - Cold start, All/most ephemeris/almanac data: 10s of kB

    - Warm start, some ephemeris data: 1-10kB

    - Hot start, no new data needed: 0B

    Meanwhile, A-GPS through nRF Cloud was said to use ~4.5kB.

    But you should be able to measure it yourself by using the %XCONNSTAT AT command.

    Best regards,

    Didrik

  • Hi Didrik,

    The nRF Cloud 4.5kB is for a cold start or warm start? What is it for the other?

    Also, does that mean that nRF Cloud is not using SUPL? What is it using?

    Regards,

    Akash

  • Akash Patel said:
    Also, does that mean that nRF Cloud is not using SUPL? What is it using?

     No, it is not using SUPL. According to the software roadmap, it is using a "packed binary format", which is sent over the MQTT connection that has already been established.

     

    Akash Patel said:
    The nRF Cloud 4.5kB is for a cold start or warm start? What is it for the other?

     I asked the application team if they had any more information. This is the answer I got:

    It looks like the total TCP payload is about 3.5 kB for A-GPS request and response, but this may vary a bit
    For a cold start all assistance data is fetched, ie almanac, ephemeris, time, location estimate etc
    For a warm start, it's assumed that only ephemeris is needed, which is about 2k for all satellites
  • Another developer on the apps team did some cold start tests with an nRF9160 Feather which is running the A-GPS sample and using a hologram.io SIM. Those tests showed 16.91kB data used:

    Note that these numbers include all the data sent between the device and the cloud, including the TLS handshakes which uses ~10kB data.

  • Hi Didrik,

    Looks like we are using this agps_write function to write the A-GPS data we have received to the modem before we switch to GPS mode. When we write the almanac/ephemeris data to the modem, is that get erased when we do a power cycle?

    From my understanding the almanac data should be valid for a several weeks and the ephemeris data should be valid for up to 2 hours. So essentially, If I write this A-GPS data, use GPS for 5 minutes, power cycle, turn on GPS again, will I have to rewrite the A-GPS data or the GPS will be able to perform a hot start?

    Regards,

    Akash

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