Doppler GPS speed and heading

My experience with GPS receivers in a range handheld GPS receivers, mobile phones and smart watches, by implementing dead reckoning (DR) to compare SOG/COG with DR speed and course supports the proposition that the SOG/COG are being generated independently of the position and time.

Velocitek, in their User Manual, asserts that the GPS unit calculates speed and heading by measuring the Doppler shift in GPS signal.

Like my Garmin watch raceQs app, the Velocitek ProStart is a yacht racing instrument which provides tactical yacht racing information relying entirely on the GPS to detect the boat's speed, course and location.

Since Garmin has been in the consumer GPS business for 30 years I would assume that they are implementing the leading edge technology in the GPS sub-systems in the current range of devices, so my question is, given that I use Toybox::Position::Info speed and heading, would it be correct for me to assert in my documentation that, like the Velocitek ProStart, the speed and heading are based on the Doppler shift in GPS signal?

dpawlyk over 6 years ago

http://insidegnss.com/how-does-a-gnss-receiver-estimate-velocity/

Alan.raceQs over 6 years ago

Thanks dpawlyk, but that link, like so many papers on the subject, only confirms there are two ways to determine speed and course but doesn't address the issue of which one is used in Garmin devices.

dpawlyk over 6 years ago

I was going to add more comments but the forum software went cranky on me.

The Velocitek Prostart is $400. For that price, it might not be doing much that is really special.

I suspect that this and the Garmins are using "inexpensive" GPS chips made by other companies.

The satellites are moving fast enough that the chips have to deal with Doppler is some form.

Poking around, it seems that using Doppler for heading/velocity might be standard for current receivers.

Alan.raceQs over 6 years ago

dpawlyk Yes indeed, the Forum does get cranky!

it seems that using Doppler for heading/velocity might be standard for current receivers.

And that's the conclusion I came to, but I'd really like to have something definite from Garmin, or someone who has been able to determine what's what in the Garmin devices.
For the life of me, I can't understand why Garmin doesn't publish the details, their secretiveness is a disappointment to me.

dpawlyk over 6 years ago

I thought it was an interesting question. So I poked around.

http://investors.st.com/news-release...croelectronics

https://www.st.com/en/positioning/teseo-liv3f.html

Alan.raceQs over 6 years ago

Great find. Unfortunately the report is over 10 years old, but the data sheet is current and makes very interesting reading.
Interestingly, I couldn't find any reference to the method used to determine speed and heading, but Section 1.1 reports position accuracy independently of velocity and heading, which would indicate that they are independently acquired.
Now we need someone to do a teardown of the devices to find out which chip is on board. Unfortunately I can't afford to destroy my devices for the exercise.

Alan.raceQs over 6 years ago

https://www.microcontrollertips.com/...heart-monitor/ has done a teardown of the FR 220 and found a Mediatek GPS receiver MTK ARM 333
https://the5krunner.com/2016/11/05/test-route-for-gps-devices/ has done lots of testing and published this analysis
https://www.dropbox.com/sh/psdyxm93y2m12j3/AABNlbBRsF2E3edvzqnnMPC4a?dl=0&preview=Test+Results+-+All+Watches.xlsx which reports a range of watches and specifies the GPS chipset.