Does Kalman filter applied on GPS receiver for PLS8-X and PHS8-US | Thales IoT Developer Community
July 28, 2017 - 3:00pm, 2841 views
Hi I am using PLS8-X and PHS8-US modem.
I read from https://softwareengineering.stackexchange.com/questions/342620/can-kalma... that receiver itself appies Kalman filter. So is it true? And how GPS finds direction and Declination in GPRMC string?
Hi !
In the PLS8-X and PHS8-X, Qualcomm chip set is used. Qualcomm has several patents in GPS with Kalman filtering., like Dilution of Precision (DOP) using multiple Kalman filters for multiple visible satellites.In order to improve the PLS8-X and PHS8-X GPS or GNSS accuracy, an A-GPS solutipn is available.
You can download assistance data that is valid for 7 days (3 days for best accuracy.
See AT manual, "GNSS Commands" and "AT^SBNW Binary Write".
In GPS based systems, an external Kalman filter is mostly used to integrate various ways of dead reckoning systems.
This is done with sensor fusion, where GPS is assisted by other sensors, like gyros, accelerometers and magnetometers (compasses). Also, various external reference signals, like DGPS, can be added.
Using complex dead reckoning, a good inside navigation (pedestrians) can be achieved.
Alsop, navigation in tunnels and other underground areas, can be achieved.
The Kalman filter is also used to ****l the realistic movement of the object and filter out the variance of the GPS signal, that can vary within meters in a few seconds - even the object remains stationary.
For example a heavy truck don't jump six meters in a second and four meter to other direction in another.
The PHS8 (and PH8) can be very accurate. Enclosed you will find my test result. The GPS was inside my office, 70cm (27.5"") from a window. As you can see, the PH8 red track was keeping it's location steadily.
A-GPS was used.
Best Regards,
Antero
Antero Markkula
Communication and Mechatronics
Enkom Active Oy – www.enkom-active.fi
Upseerinkatu 3 A, 02600 Espoo, Finland
Mobile: +358 400 411368
Office: +358 10 204 0000
Fax: +358 10 204 0010
E-mail: antero.markkula@enkom-active.fi
Thank you for your reply.
As you said and from command sheet I found,
"GpsOneXTRA assistance data is valid for up to 7 days." then what after 7 days? And how AT^SBNW command works? I understand flow how to aply binary file but is this one time process?
Also in PHS8-US currently without A-GPS, location is not steady. Event if GPS is on the same place, I get different values for location and also sometimes I get speed from GPS.
Hello,
After 7 days the GpsOneXTRA data is no longer valid and won't help any more. A new file ***** to be downloaded from the web service and loaded to the module. There is a description in the AT Commands specification document.
Regards,
Bartłomiej
So for A-GPS, I need to write a application which will donwload new file after every week and load to module.
Hi!
GPS on general, is statistically accurate. The measurement varies over time, and it is normal to get different location at the same place. Most GPS receivers provide horizontal accuracy of 3 meters 95% of the time.
Various conditions, like Geometric/Position Dilution of Precision, Atmosphere Refraction, Multipath Effect and Satellite Time and Location (Ephemeris). The last one can be improved with A-GPS, that can be used to store estimated information or give more accurate information in real time.
See images on this page: http://blog.oplopanax.ca/2012/11/calculating-gps-accuracy/
Best regards,
Antero
Antero Markkula
Communication and Mechatronics
Enkom Active Oy – www.enkom-active.fi
Upseerinkatu 3 A, 02600 Espoo, Finland
Mobile: +358 400 411368
Office: +358 10 204 0000
Fax: +358 10 204 0010
E-mail: antero.markkula@enkom-active.fi