get GPS signal strength

Discussion in 'GPS Technical Discussion' started by jura87, Apr 5, 2016.

  1. jura87

    jura87

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    Hello,
    I am new to this forum...so hello everyone and thank you for any kind of help:)
    I am using GPS module and i want to calculate the signal strength from the received GPS information.
    GPS NMEA parameters i have available:
    HDOP, PDOP, VDOP, Fix Mode, GPS Satellites in View, GNSS Satellites in View, Satelites Used, C/N0.
    Can anyone help me with this? to get some kind of signal strength information...

    thanks
     
    jura87, Apr 5, 2016
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  2. jura87

    Nuvi-Nebie Moderator

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    Signal strength is the received power level from a single transmitter, in the case of a GPS receiver, it is using signals received from many (possibly 20 or more), satellites, each of which will have a certain signal strength, a combined signal strength measurement will not indicate positional accuracy. If positional accuracy is what you require, the HDOP, VDOP, PDOP, and TDOP values can be used to calculate a DOP or Dilution of precision. Accuracy in GPSs is often displayed as a distance in Metres (or feet) that the unit may be from it's true position, with a low figure showing better accuracy
     
    Nuvi-Nebie, Apr 5, 2016
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  3. jura87

    jura87

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    Thanks for the reply.
    I was wondering if i could calculate some kind of signal strength from HDOP, VDOP, PDOP and number of satellites...But based on your explanation with those data i can only get accuracy right...?
    What about if i use only satellites in view? ifor example:
    4 satelites - 1
    7 satelites - 2
    10 satelites - 3
    15 satelites - 4
    >15 satelites - 5

    Or could i use parameter C/N0 (carrier to noise ratio)?
    i would like to implement from this data some kind of good(not perfect) signal strength indicator?

    thank you
     
    jura87, Apr 5, 2016
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  4. jura87

    Nuvi-Nebie Moderator

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    It really depends what you want to do with this signal 'strength indicator', what would you use it for?. There are several items that could be measured, number of satellites in view is one, but a better one would be number of satellites being used, i.e. number of satellites that the GPS is getting usable data from. Counting satellites in use will only be a rough guide because it will depend where they are relative to the GPS receiver, 4 well spaced satellites is better that 20 that are very close together.

    If your GPS unit has got a 'fix' then the DOP / accuracy in metres is the best indication of how well the unit is performing, signal strength isn't a useful thing to measure because it is all or nothing for the GPS receiver, it either gets good data form each satellite of it doesn't
     
    Nuvi-Nebie, Apr 5, 2016
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  5. jura87

    jura87

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    I have a gps modul from wich i get lat and lon data without problems... I am sending this data through gprs modul to my web server...what i want to achive is that i want to send gps signal quality information to the server also... So you say c/n0 parameter is not useful for this?
    For DOP values i get HDOP PDOP and VDOP without TDOP... what if i use number of used satelites and HDOP? I know that the smaller the hdop more acurate is position...
    Can you maybe suggest me some kind of formula based on HDOP and used satelites?
    Actualiy i want to have indicator with values 1-10.. Where 10 is excellent and 1 is bad gps signal...i am realy having hard time to figure out this one...
     
    jura87, Apr 5, 2016
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  6. jura87

    Nuvi-Nebie Moderator

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    There are some formulas for calculating DOP on the net (click HERE), I don't think signal to noise ratio (SNR) info. is very useful, as I said earlier, the GPS either gets usable data or it doesn't. Unlike with TV / Radio broadcasts where both the transmitter and receiver are stationary and SNR can be useful for aligning antennae correctly, I would say that signal quality (the ability to get useful data) is more important.

    I would say "number of used satellites and HDOP" is a much better indicator than signal strength / SNR
     
    Nuvi-Nebie, Apr 6, 2016
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  7. jura87

    jura87

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    jura87, Apr 6, 2016
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  8. jura87

    jura87

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    hello,
    Thanks for your help...really appreciate it!
    I found one basics GPS article...which is saying that we can look also only for PDOP value...so i am wondering i use only this measure... what do you say?

    thanks man!
     
    jura87, Apr 6, 2016
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