GPS signal


How can the signal strength of GPS be measured?
Is there something like GPS RSSI?

How about GPS accuracy?
Is there an AT command for that that returns accuracy value?

If all these are not possible, how about determining if signal is available or not?

Thanks in advance.


For GPS accuracy, the magic words to look up in the AT command set are Dilution of Precision. You should be able to get at least the PDOP, HDOP and VDOP values which will give estimates of the current accuracy of location in the horizontal (HDOP) plane, vertical (VDOP) plane and an overall indication (PDOP).

Ciao, Dave

EDIT: try enabling the GSA sentence (GPS_NMEA_GGSA_EN) using AT+GPSNMEA. This sentence contains all the active satellites used in the current fix, the signal strength of these satellites as well as HDOP, VDOP and PDOP values.

Ciao, Dave

Hi Dave,


I don’t have the HL6528 Development Kit on hand yet.
Will try your recommendations once DevKit arrived.

I’m studying AT commands as of the moment and maybe missed that GPS accuracy command or it may not be explicitly stated in AT commands reference guide.

Will update this thread once tested.

EDIT: looks like HL6528 doesn’t have the HL6528-G. If so, testing of GPS can only be done during board bring-up.

Thanks again.


No Problems.

It’s not explicitly stated as an AT command - you have to know what’s available in the NMEA sentences.

You could also look at what’s available in the PVT output - that might be easier to parse than having to dig through multiple NMEA sentences to grab a bit from one and more from another…

ciao, Dave

Hi Dave,

How about signal jam (+KJAM)?
Can it be translated to signal quality?



I doubt it - +kjam is to do with GSM radio jamming, not GPS. The GSA NMEA sentence gives you the signal strengths of the satellites (Space Vehicles or SVs) used to generate the current GPS fix.

If you’re interested in the GSM radio signal strength, start with +CSQ to get the rssi and ber. The also appears to be $ CSQ which is similar. There are other commands to dig out the cell signal info etc. Search the at guide for signal quality and signal strength.

Ciao, Dave

Hi Dave,

Thanks. I’ve overlooked kjam.

I saw some signal to noise ratio (signal quality) values in NMEA sentence.
I’ll just identify which value will give the most accurate signal quality.

BTW, I can’t find an application note on gps from sierra wireless.
Can you suggest other sources for this?
Code snippet can be better.



Not sure what you’re trying to do here.

The best way to work out the quality (and thus the accuracy) of the fix (or Position Solution) is to use the [H|D|P] Dilution of Precision values. These are supplied by the GPS engine and are based on the SV’s used to generate the fix. There is a table that maps the DOP values to an estimated position accuracy - have a look at this wiki article.

SV signal strength is available straight from the NMEA sentence if you’re trying to do something funky and map signal propagation or something. But it’s only for the SVs listed… and as GPS uses multiple SVs (min 3 for 2D solution, preferably 4 or more for 3D solution) you don’t know WHICH SVs the GPS engine has used for the solution.

For some good info on GPS and how it works, have a look at the Whitepapers section on the GPSd site.

Hope this helps.

ciao, Dave

Hi Dave,

Your suggestions are really of great help.

I also noticed a Sierra wireless proprietary NMEA sentence that claims to “provide information about the accuracy of the positioning solution”.

It is in page 696 of HL6/HL8 AT command Interface Guide rev 7.

Sample output: $PSWI,SA,1,4,1,5.0,7.5*27
*5.0 is “Estimated Horizontal Position Error (meters)”
7.527 is “Estimated Vertical Position Error (meters)”

I think of using this instead of DOP and the values are already in meters (distance).
What do you think of this?



That proprietary sentence sounds like a good plan.

Also, have a look at the section in the manual about PVT sentences. One of the problems with NMEA output is that you need to get a number of sentences to get a complete solution. I understand that the PVT sentences bring out more of the complete solution information in less sentences.

Ciao, Dave

Hi Friends,

i am working on the Vehicle tracking & i am using HL6582-G2.8V module with Firmware “HL6N_003_00_200F_p7176B”

i am starting the GNSS by applying AT+GPSSTART=0 & AT+GPSNMEA=1,1,0005,81 to collect the NMEA Frames & logging in txt pad for 9 to 10 Hours.

then plotting these data’s in Google map using & i observe there is no stability in location data its wandering.(image attached for reference)

due to this issue when i measure distance travel report for the vehicle i am getting around 10KM & above even when the vehicle is in stable position.

please guide me if anyone have solution for this.
Internal Antenna with trinity board.log (616 KB)