# GPS Speed Inaccuracies

### 7 thoughts on “GPS Speed Inaccuracies”

1. I’m using HE910 modules running firmware 12.00.003 (GPSSW: 1:0:0)

They appear to report the correct location (lat/long) but are not reporting the correct speed.

After the module acquires lock, I execute the AT\$GPSACP command
roughly once every 5 seconds.  While driving, it appears that the
latitude and longitude that are returned are correct, however the
speed (and sometimes the heading) is not.  Often the speed
reported with the GPSACP and GPRMC responses stay below 1 kmh and
1 knot regardless of the speed of the vehicle it is travelling in.

To make the problem more clear, in my example below I have calculated the
point to point (rough MPH) speed, which I have calculated as the
distance between the lat/long points returned by the GPSACP
command.  This isn’t exact, but it was very close to what my
speedometer was reading at each point.

I have tried 3 different antennas with 2 different HE910s, always with the same result.

Any help would be appreciated.  Thanks!

————————————————————————————————-

Here are the commands I have sent after power up:

AT+CGMR

12.00.003

OK

AT\$GPSSW

\$GPSSW: 1:0:0

OK

AT\$GPSP=1

OK

AT\$GPSQOS=100,50,25,0,0,0,1

OK

AT\$GPSNMUN=2,1,0,1,0,1,0

OK

————————————————————————————————-

Here’s an example of the output I am getting minutes after acquiring GPS lock:

AT\$GPSACP

\$GPSACP: 170848.000,3330.3120N,11206.2502W,0.75,332.0,3,179.04,0.48,0.26,080413,09

OK

\$GPGGA,170849.000,3330.3049,N,11206.2502,W,1,09,0.75,332.0,M,,M,,0000*66

\$GPGSA,A,3,01,11,12,14,18,19,22,25,31,,,,1.75,0.75,1.25*06

\$GPRMC,170849.000,A,3330.3049,N,11206.2502,W,0.25,179.04,080413,,,E*75

\$GPGGA,170850.000,3330.2978,N,11206.2502,W,1,09,0.75,332.0,M,,M,,0000*64

\$GPGSA,A,3,01,11,12,14,18,19,22,25,31,,,,1.75,0.75,1.25*06

\$GPRMC,170850.000,A,3330.2978,N,11206.2502,W,0.25,000.00,080413,,,E*7C

\$GPGGA,170851.000,3330.2914,N,11206.2502,W,1,09,0.75,331.0,M,,M,,0000*6C

\$GPGSA,A,3,01,11,12,14,18,19,22,25,31,,,,1.75,0.75,1.25*06

\$GPRMC,170851.000,A,3330.2914,N,11206.2502,W,0.22,179.04,080413,,,E*7B

\$GPGGA,170852.000,3330.2862,N,11206.2502,W,1,09,0.75,331.0,M,,M,,0000*6F

\$GPGSA,A,3,01,11,12,14,18,19,22,25,31,,,,1.75,0.75,1.25*06

\$GPRMC,170852.000,A,3330.2862,N,11206.2502,W,0.17,179.04,080413,,,E*7E

\$GPGGA,170853.000,3330.2817,N,11206.2502,W,1,09,0.75,332.0,M,,M,,0000*6F

\$GPGSA,A,3,01,11,12,14,18,19,22,25,31,,,,1.75,0.75,1.25*06

AT\$GPSACP

\$GPSACP: 170854.000,3330.2785N,11206.2502W,0.75,331.0,3,176.36,0.20,0.11,080413,09

OK

Point to Point Speed MPH: 23.20 (rough)

1. Hi Jeff,

thanks for this. We are working on it and we will update you in short time to provide you a solution.

1. Andrea,

I found another GPS issue which might be related and might help you guys.

After multiple days of use the GPS will sometimes also "lock up".  I will still get NMEA data, but the NMEA data and the GPSACP command will respond with an old time and location.  The time fields on all the responses appear to remain static and will not increment.

While in this "locked up" state:

I issued a "Hot Start" command  (AT\$GPSR=3) and after 10 minutes, I could not get any valid time or location from the GPS.

Next, I issued a "factory reset" (AT\$GPSR=0) and the device reset properly and was able to regain GPS lock in only a few seconds.

In this instance, the factory reset worked but the hot start didn’t.  My guess is the problem might be related to the almanac / ephemeris being corrupted in memory.

2. Andrea,

Do you have any updates on this?  I have a large client looking to use these in the field as soon as possible.

Thanks!

1. Hi Jeff,

I apologize for the late reply. Are you still testing the 12.00.003 ?

I asked our local support in US to contact you to better analyse the issue you are having with the GPS. Are you in contact with them?

1. Andrea,

I am still using 12.00.003.  My domestic supplier said that there will be a new firmware version coming out that will fix this issue.  Has there been a release since 12.00.003?

I haven’t heard from any local support yet.

Thanks!

1. We should release a new version 12.00.004 end of June with GPS improvements, HTTP client, eCall and other features.