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Why are no SV used in solution?

DAllo
Associate II

[code]

$GPGSV,3,1,09,16,73,203,,27,60,279,,21,50,066,,26,47,165,*7C

$GPGSV,3,2,09,20,39,119,,08,25,276,,10,23,144,,07,21,315,*7E

$GPGSV,3,3,09,19,00,000,26,,,,,,,,,,,,*4C

$GLGSV,3,1,10,88,77,350,,79,50,302,,78,47,212,,81,39,260,*60

$GLGSV,3,2,10,87,36,057,,72,26,066,,71,17,014,,65,13,111,*69

$GLGSV,3,3,10,80,08,339,,77,05,179,,,,,,,,,*67

[/code]

This is the state after around 60 seconds. I have the above SV viability, what would be the reason that i'm not seeing the CN0 ratios, or that the SVs are not being used for a solution?

Around 5 mins later, I have the following, but still am seeing many more sats than are used in fix, and not getting CN0 for some still.

[code]

$GPRMC,111752.000,V,5400.00000,N,00300.00000,W,0.0,0.0,270419,,,N*6E

$GPGGA,111752.000,5400.00000,N,00300.00000,W,0,02,99.0,060.00,M,0.0,M,,*78

$GPVTG,0.0,T,,M,0.0,N,0.0,K,N*02

$GNGSA,A,1,06,,,,,,,,,,,,99.0,99.0,99.0*18

$GNGSA,A,1,76,,,,,,,,,,,,99.0,99.0,99.0*1F

$GPGSV,3,1,12,12,72,069,21,25,66,252,,32,46,275,,14,39,299,*7E

$GPGSV,3,2,12,24,35,129,25,29,24,186,,06,20,062,30,02,19,100,26*78

$GPGSV,3,3,12,31,16,297,,19,15,038,20,22,07,331,,03,06,350,*73

$GLGSV,2,1,08,76,65,067,26,86,43,125,,77,41,294,,85,38,044,*6A

$GLGSV,2,2,08,67,34,278,,75,23,091,,68,21,338,,66,13,227,*6D

$GPGLL,5400.00000,N,00300.00000,W,111752.000,V,N*50

$PSTMCPU,41.93,-1,49*40

[/code]

2 REPLIES 2
Francesco Virlinzi
ST Employee

Hi

Internally in the GNSS algorithm there are several threshold to involve or not a satellite in the PVT solution.

These thresholds can be modified:

CDB-ID 132 – GNSS Positioning CN0 threshold

CDB-ID 198 – GNSS Mask angle positioning

this means that also if a satellites is seen ... it isn't involved in PVT solution because its params are under a threshold.

Hope this helps

Regards

Francesco

Thanks for your answer, it's very helpful. Is there a reason that CN0 isn't being reported in the *GSV messages for the majority of these satellites? I see their elevation and azimuth but the SNR/CN0 field is very often empty.