No GPS fix at all (occasionally), location inaccuracy (occasionally), LTE stops working (around a specific place)



  • Hello,

    No GPS fix at all (occasionally)
    Today I was testing accuracy of GPS pytracks. Currently, I have two pytracks. Let's call them GPS_A and GPS_B. I started testing GPS_A. I plugged in the power bank and after waiting for like 15 minutes I did not get the fix. I tried this two times. I thought maybe something was wrong with GPS_A.
    So, I switched to GPS_B. I was able to perform two accuracy tests where I walked over 2 Km and returned back to original location. I wanted to do 3rd test on GPS_B and suddenly it did not get fix at all 3rd time. I tried waiting over 15 minutes two times.
    I power cycled every time I started working with GPS to make sure cold started GPS module.

    location inaccuracy (occasionally)
    Green dot shows my starting location. Also, for Test number 1 performed with GPS A the location jumped across the across road as soon as I started moving. The red line shows the actual path traveled by me and markers shows the location detected by GPS_B.
    maps_1.PNG

    For Test number 2 performed with GPS B the location was more or less accurate enough.
    maps_2.PNG

    LTE stops working (around a specific place)
    The orange line in above two pictures shows place where there are alot of overhead power lines.

    1. Why I do not get any fix at all sometimes ?
    2. What could be the possible reason that it GPS location jumped across road for Test number 1 as soon I started moving ?
    3. Could power lines be the issue that LTE stops works at around that place. It is a busy area with alot of traffic lights and cars.


  • @jcaron mmmmhhh.... looking back at what’s left of your satellite pictures it seems to be a lot less dense than I initially thought.

    It would be interesting to log more information from the GPS chip, it can provide a lot of information including how many satellites are visible and used, which ones, and so on.

    Recording the full output should allow you to “play it back” later in dedicated tools for this.



  • @smarok what library are you using to parse the chip’s results? The chip can lock into either GPS or Glonass satellites, and some libraries will only support reports by one and not the other.

    Also, geolocation requires a good unobstructed view of several satellites. Dense urban environments with narrow streets and tall buildings (so-called “urban canyons”) are not ideal for pure GNSS positioning. That’s one of the reasons many devices use other sources for positioning, including nearby Wi-Fi networks and dead reckoning.

    Standard GPS accuracy without augmentation/differential GPS (high precision corrections for atmospheric disturbances) is on the order of a few meters. Whenever the chip loses sight of satellites and the solution “degrades”, this can increase to a few dozen meters.

    We’re missing scale information on your maps, so it’s difficult to know if we are within the tolerances of GPS.

    As for cellular reception, as always, there can be holes in coverage. Again, dense urban environments are not necessarily the best friends of radio networks. Depending on the network in use, the band in use, location of the cell towers, and so on, it may be difficult for the radio signal (which prefers line of sight) to travel from the tower to your device or vice versa.

    I know at home I have 2 cell towers for the network I use within a few hundred meters, one on each side. But with buildings in between in both cases, reception can be miserable (and I’m talking about a regular phone here).

    In some countries you can find out the positions of cell towers for various networks and the technologies and bands available on each. This can be quite instructive.


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