[est31]

> GPS is being modernized to use a 13-bit Week Number

If you want to dig into the details, this is one of the specification documents of the GPS signal [1].

"Figure 40-1. Data Format (sheet 1 of 11)" displays the layout of the legacy messages LNAV, while "Figure 30-6.Message Type 33 -Clock & UTC" displays the layout of the new CNAV messages. You can see that WN in the old message has 10 bits only, while WN_{ot} has 13 bits in the new message.

13 bits are a bit short IMO. It's 157 years instead of 20. Just puts the rollover into that uncanny valley where you forget about it too easily. Instead, IMO one could have extended it to 32 bits directly, which would be enough for 82 million years. In the CNAV messages, there are 53 bits of reserved space around, so it's not like that bits are super scarce, and if they are you could take from the reserved space.

[1]: https://www.gps.gov/technical/icwg/IS-GPS-200J.pdf

[stonogo]

If we're still using this protocol 158 years on we've got bigger fish to fry.

[grecy]

It's accurate to within a meter and works perfectly fine today, without us having to spend billions more on a replacement that could surely be spent on those pesky problems like healthcare or education.

Why wouldn't we keep using it for hundreds of years to come?

[dzhiurgis]

IDK because European ones already work down to the centimeter...

I've just sailed into 2-3 meter wide canal after dark here in NZ. Used my previous track from earlier today. 1 meter accuracy is not precise enough to do it safely - had to look for fairly poorly lit nav marks and rocks.

[jniedrauer]

I wouldn't trust GPS down to sub-meter precision even if the spec technically supported it. I often travel a route, then turn around and retrace the exact same route, only to see the GPX data indicate fairly large variances. LEO is very large and the atmosphere is not uniform.

[craftyguy]

Or you could use lights and your eyes.. Blindly trusting anything like GPS to guide you through risky situations like that sounds like a good way to ruin your boat.

[dzhiurgis]

I would still do, but you use GPS as a confirmation rather than source of truth.

[throw0101a]

> Or you could use lights and your eyes..

Assuming there's no thick fog.

Though radar, depending on its resolution (which is determined by array/beam width), is also handy.

[7952]

You have to replace the satellites periodically anyway so you are already spending lots of money.

[grecy]

Sure, so spend just enough to replace them with same, rather than extra billions to develop something new.

[whatshisface]

Why stop at a meter?

[jrockway]

The error beyond this level is due to local ionospheric conditions rather than the protocol. Corrections can be transmitted to interested receivers, WAAS is an example of such a system.

cm level accuracy is available with RTK. It works by comparing GPS signals from a known nearby location with that of a mobile receiver, providing what amounts to especially good correction. It works fine and you can get started at home for <$100.

A new protocol that does better than what we have right now will take some major breakthroughs.

[tecleandor]

Any recommendations on what hardware or project should I look for to "start at home"? Sounds interesting...

[modernerd]

http://rtkexplorer.com/how-to/posts-getting-started/

[ac29]

You can get cm level accuracy with RTK: https://en.wikipedia.org/wiki/Real-time_kinematic

[mehrdadn]

This looks amazing. Any idea if there are consumer level CPGPS devices?

[labster]

Kessler syndrome.

[froh]

I had to look it up... https://en.m.wikipedia.org/wiki/Kessler_syndrome

The Kessler syndrome (also called the Kessler effect,[1][2] collisional cascading or ablation cascade), proposed by the NASA scientist Donald J. Kessler in 1978, is a scenario in which the density of objects in low Earth orbit (LEO) is high enough that collisions between objects could cause a cascade where each collision generates space debris that increases the likelihood of further collisions.

[jniedrauer]

> I had to look it up...

You're a disappointment as a nerd. As penance, go watch Planetes.

[labster]

He's one of today's lucky 10000. No insults please, Tanabe-san would be disappointed.

[ChrisSD]

Why not go in the other direction? Make the rollover happen every few years as just a normal part of operation. It means it'll be a well tested code path.

Are there physical reason why that wouldn't work?

[lifthrasiir]

It would preclude the existence of long-running GPS devices. I'm pretty sure that, in addition to devices that never have tested the rollover scenario, there are actually older devices produced in 2000s and still running today.