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GPS+GLONASS: How does it work? Will loss of GLONASS lead to loss of positional data?

Former Member over 9 years ago

Does anyone have any in-depth knowledge of or have a link to an article or literature about how GPS + GLONASS actually works within Garmin's software/hardware?

Specifically, if the GLONASS signal becomes unreliable, does the 235 discard the GLONASS data and revert back to GPS-only data or does it simply stop recording positional data all together?

The reason I ask is because of the 19 activities I've logged since owning the watch (all with GPS+GLONASS enabled), 3 have lost position data at some point in the run and only one of those has ever regained it during the run. The watch was worn on the outside of the left wrist on two activities, and inside of the left wrist on the latest. The watch was exposed (not under clothing) on all three of the loss-of-data runs.

In the 5+ years of owning Garmin hiking/running devices, I've never lost GPS signal in the middle of an activity (unless, understandably, going through a tunnel or deep canyon). These three instances did not involve any type of terrain where GPS signal loss should have been a problem, hence why I suspect GLONASS reliability.

Then again, maybe I just have a defective unit. Any thoughts?

Thanks!

0 Former Member over 9 years ago

GPS uses 31 satellites, where the Russian operated GLONASS uses 24. I've heard using the two together helps where you may be in a bad spot for one system, but in line for a satellite from the other system. This is suppose to work well in built up areas. I don't know for sure, but maybe the FR235 is locking on one system and if it loses that signal it's having difficulties switching to the other? You ask a very good question and hopefully someone has the answer.

0 mariomobiel over 9 years ago

Found some interesting links on the web about this.

http://gpsworld.com/test-shows-galileo-increases-accuracy-of-location-based-services/

So far I couldn't find any info about what happens if one of the signals drops...

0 Former Member over 9 years ago

Thanks for the link.

As a follow-up thought to ponder to my original question, what happens when the GPS signal and GLONASS signal are present but do not agree. Does the watch discard GLONASS, does it take some combination of the two and place you in the middle, or does it simply drop both signals until it reaches some threshold of agreement?

0 timgrose over 9 years ago

Thanks for the link.

As a follow-up thought to ponder to my original question, what happens when the GPS signal and GLONASS signal are present but do not agree. Does the watch discard GLONASS, does it take some combination of the two and place you in the middle, or does it simply drop both signals until it reaches some threshold of agreement?

I am very doubt if information like this on exactly how the two sets of satellites are blended makes out into the public domain for commercial reasons (and no I have no idea anyway!).

All that I can observe is that there is no GLONASS only mode so, one presumes, GPS ones are probably taken in some sort of priority.

0 NickMN over 9 years ago

soft reset

I would make sure your firmware is up to date... and to do a soft reset . That is what DC Rainmaker recommends when gps data doesn't seem right. Really when any electronic doesn't work...reboot!

Next step would be to start a return/warranty/service process with support (telling them that you updated and restarted firmware)

0 Former Member over 9 years ago

Since Firmware 4.1 was released on 23 Feb 2016, I have accomplished 36 activities with no signal loss. Customer support wouldn't/was unable to tell me what the "various bug fixes and stability improvements" were with the update, but perhaps this problem was fixed. So far, so good.