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How did L5 get enabled and still leave us with an accuracy worse than 3.5m? Wasn't it supposed to give us 30cm? What happened to that? https://en.wikipedia.org/wiki/Global_Positioning_System

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Don't quote me but I believe you have to use both bands to get that accuracy. Some devices support it. https://support.garmin.com/en-NZ/?faq=9NWiPDU4gM0JWMfdWFol7A.

Real life test https://www.dcrainmaker.com/2022/04/garmin-vertix-accuracy.h...

Thanks. I've tried a phone with support for both L1 and L5 (and other systems) and I don't notice any improvements over my old phone. In fact it seems to take longer to get a fix. I would love to hear if anyone has found a phone that actually gets significantly better performance with L5.

Time to get a fix is mostly what clever techniques the receiver uses. There are various papers demonstrating getting a fix that is probably correct with just a few milliseconds of signal and then lots of processing.

You also have to cut corners to get a (probably correct) fix fast. Things like assuming the almanac hasn't changed since last time, the user hasn't moved more than a few hundred miles, the system clock hasn't drifted by more than a second or so, and no satellites have become unhealthy.

I've always noticed my Garmin watch gets a fix extremely fast except for the first time I use it after traveling somewhere new. That first one always takes several minutes.

yes, the math is significantly simplified if you assume you haven't moved. cold start is always much slower (and is called out as such in most GPS datasheets)

> Things like assuming the almanac hasn't changed since last time, the user hasn't moved more than a few hundred miles, the system clock hasn't drifted by more than a second or so, and no satellites have become unhealthy.

If you are using a smartphone, you could probably validate those assumptions via your other sensors?

Google hosted the Google decimeter challenge, which used post processing of data from dual band phones to try and get as good accuracy as possible. The top submissions got an accuracy of just over one meter.

I have a phone with dual band GNSS, and it's by far the best location accuracy I've had in any device. I can see which side of the cycle path I've been on, and it regularly works indoors. I don't live where there are tall buildings though, but even at fairly open space my older devices gave worse results. And I get a fix within seconds thanks to A-GPS.

https://www.kaggle.com/competitions/smartphone-decimeter-202...

My pixel 6 pro has much, much better GPS accuracy than my pixel 3 had.

Here is a comparison between my pixel 6 and my S.O.'s pixel 2, from a hike we did recently: https://imgur.com/a/5VibEUw

This makes it pretty obvious how much the L5 band can improve GPS. These were good conditions in general, but just looking at the bottom right portion alone shows how good L1 + L5 in a phone can get. I'm sure devices with larger antennas (bike computers, larger handheld GPS units, etc) can do even better in worse conditions as well.

Interesting. Did you try comparing it against anything other than a Pixel 2 by any chance (to rule out the Pixel 2 just being worse than better L1 phones)? And have you tried it in the city to see if L5 is any help there?

I have compared it against both the pixel 2 and the pixel 3 xl I previously had. In more urban areas with buildings around it definitely still performs a lot better.

Previously on walks around the neighbourhood gps tracks would just be a general location and bounce around. I can now see pretty regularly which side of the street I was on, street crossings, etc.

Not all of the satellites have L5 either. As of today only 16.

GPS used in survey equipment is accurate to 2cm with ~5 second acquisition time.

This may be differential gps with a local reference

RTK GPS can be 1cm accuracy with sub second time.

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