RTK cold/hot start + reacquisition times

Reach Module / M+ / M2 RTK / PPK configuration
1

I am interested in knowing following performance of Reach in clear sky, suburban and urban scenario:

  • Cold Start (time to first fix)
  • Hot Start (GNSS signal outages between 30 and 50 seconds)
  • Reacquisition (GNSS signal outages between 1 and 5 seconds)

If the terms are familiar to you they are taken from the Piksi Multi product summary - I am just interested how much L1 solution is worse than an affordable L1/L2. I guess L1 will have all the times much longer, right? And is it also much more dependent on signal quality (very clear sky) since only single frequency is used? Can we get some average numbers here?

2

Here are your performance figures:

Reach_TTFF
Reach_TTFF.png976×134 7.18 KB

(the footnote1 says all satellites at -130dBm which I take to mean “good satellite reception”)

Beware though:

In this context, the word "fix" has little to do with the RTK status of "single, float, fix." Here, what "fix" means in simple terms is: "How long it takes before the GNSS receiver can output my position." This means you could take, for example a handheld Garmin unit, turn it on, and count the seconds until you see your location show up on the screen. That would be your number for: Cold start TTFF.
But! I think what you really wanted to ask is, "How long do I have to wait for an RTK status of fix?"

And the answer to that from boot-up is generally a few seconds with multi-frequency, and a few minutes with L1-only. Reaquisition is faster.

3

Yes you are right, I am talking about FIX as in RTK solution. I am looking for concrete tests with concrete numbers.

4

Yes, it would be nice to see a chart/table/graph of such. I think that other than open-sky results, everything else would be hard to call ‘concrete’ without really nailing down the environmental parameters. Plus, with L1, there is some knowledge you gain through experience that gets you the concrete results.

On the other hand, L1/L2 in sub-optimal conditions does not require near as much of that knowledge though experience. This is a bad analogy, but you could liken L1 to being able to play a guitar, and L1/L2 to being able to play ‘Guitar Hero.’ OK, it is not that much difference or nearly that hard, but I couldn’t resist! :laughing: I know I just offended some people - sorry about that. :slight_smile:

5

There is also some technical talk over at the Drotek M8P forum including time to fix times.

6

If you restart solution on Reach RS while using GPS+GALILEO+GLONASS with half the sky blocked it will snap into a fix in about 40s. This is what I get when testing in front of our office. Your experience might vary depending on the baseline and source of corrections.

2 Likes
7

The restart you talk about is similar say to 1s signal outage after fixed solution right? That would equal the reacquisition on Piski - so it is 40s vs 2s. Interesting. Will 100% clear sky help to get even faster refix?

8

I would compare it to a hot start, not reacquisition. With 100% clear sky and some tweaks, like sending base position more often we can probably shave off another 10s. However for real-life applications I do not see it being really significant.

L1/L2 fix time will also depend on conditions heavily. Have seen all kinds of receivers and simply “having L2” is not a guarantee of good performance.

9

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