Re: SparkFun GNSS L1/L5 Breakout - NEO-F10N, SMA - GPS-24114 - SparkFun Electronics

[Greg Troxel]

Chris Kuethe <chris.kuethe@gmail.com> writes:

> I saw a brief comparison of GNSSes that said GPS has better accuracy than
> GLONASS, and that Beidou and Galileo have similar accuracy which is better
> than both GPS or GLONASS. I'm not really equipped to properly
> test/validate/refute that claim, or even appreciate it.

Per-system accuracy is one thing, and net accuracy from an ensemble is
another.  It's also not just accuracy, it's odds of working.

> OK, it's cool that
> my cell phone can simultaneously use GPS (L1/L5), GLONASS (L1), Beidou
> (B1/B2a), and Galileo (E1/E5a). I've got a home time server which I haven't
> bothered to measure cable propagation delay or interrupt latency on because
> 1-millisecond time sync is quite sufficient for my uses (log file
> timestamps, correctly setting the time on my telescope controller, and
> programming the timer on my coffee maker). I would hope that my
> multi-constellation receivers are all smart enough to figure out which
> combination of satellites provides the best navigation solution..

The L1/L5 is interesting, vs L1/L2.    I don't really understand why
there are L1/L5 only receivers given how L2/L5 are close.   It may be a
perception that L2 is going away, but that seems premature.  My
impression that there are more L2 signals available than L5, but maybe
with Galileo that isn't true.

> Gary share his thoughts about why an absence of GLONASS support might be a
> feature; from my perspective it doesn't seem to offer any compelling
> advantages over GPS. It doesn't look like civilian multi-frequency are
> readily commercially available which would allow you to directly probe
> ionospheric effects. If you've got limited resources (tuners, correlators,
> DSPs, memory, CPU) in your receiver, maybe you want to use more of them for
> more useful systems. At least GPS has some usable L5 satellites.

Prioritization schemes are one thing, but most receivers these days have
a ton of channels.

I speculate, wildly and without basis, that the GLONASS signal structure
being different (not just CDMA) is a reason that omitting it can result
in a lower cost, both BOM and NRE.  And that with Galileo and BeiDou,
skipping GLONASS doesn't hurt much.

> I dunno, maybe you have really restricted sky view in one location and
> GPS+GLONASS might give you just enough satellites to get a usable fix?

Indeed, a fair point.   But I find in a multi-constellation receiver
that there are often 30 sats above the horizon.