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Super-Accurate GPS Chips Coming to Smartphones in 2018

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Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#101

Post by yaantc »

Deadolus wrote: post #70
lhl wrote: post #34

If anyone works in the field, I'd be interested in how this dual signal (L1/L5) chip interacts with the RTK/CPGPS [1] (which improves accuracy down to 1-3cm already (at the cost of using multiple GPS units)). RTK is commonly used in survey drones, and kits are available for about $1K. [1] https://en.wikipedia.org/wiki/Real_Time_Kinematic

RTK uses a fixed base station, ideally you know exactly where it is so that you know the exact location of your mobile unit (else you will at least get a pretty good relative position). With the new chips, Broadcom, u-blox and others are bringing to market now you are no longer dependend on a base station to get cm-level accuracy. Instead they exploit the different properties of the L1/L5 frequencies to infer stuff a…

Also, RTK requires tracking the carrier phase. And in turns this requires the receiver being kept on all the time, which is power hungry and just not acceptable for low-power / on battery applications.

Whereas the dual frequency approach can be used in the same way as "regular" GNSS, using all the low-power tricks to sleep as much as possible (with some accuracy vs. power trade-offs). Of course there will be a power consumption penalty vs. a single frequency receiver: the two RF chains, and the extra base-band processing. The later can be mitigated by better nodes (the article mention the chip being 28nm, so low dynamic power). The two RF chains impact of course can't be avoided. But for some application it may be worth it.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#103

Post by makomk »

userbinator wrote: post #37
ifoundthetao wrote: post #25

Earlier quoted context omitted.

Boy do I miss those types of sites. I need to find more of them.

Here's another, very detailed 4-part "build your own GPS" article from the early 90s: http://lea.hamradio.si/~s53mv/navsats/theory.html No FPGAs, RPis, or SDRs --- it's mostly done in discrete logic with a 68000 doing the back-end processing. As a bonus, he also implemented GLONASS. Furthermore, the software takes up less than 32KB of ROM.

Note that while well explained, this is a very 90s way of implementing a GPS receiver. As I understand it modern receivers use FFT-based correlators that have much better cold-start performance than the old-fashioned design because they can test very large numbers of possible correlations at once (generally hundreds of thousands of them).

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#104

Post by noen »

dmckeon wrote: post #27

Down to 30cm - good! Now all we need is a GPS-enabled app for urban pedestrians that reminds them to look left or right just before they step off a curb into oncoming traffic.

Actually, I was part of a team that built a GPS based walking navigation system for the blind (Google Microsoft Cities Unlocked). The limits of 5m accuracy were an incredible danger that prevented us from doing any u assisted trials.

Even highly trained and skilled cane users would wander into the roadway usually within 10-15 minutes of using the system, purely because of GPS drift. And forget about ever using it in urban centers. In London, Boston and NYC it was rare to be more accurate than 50-100m. It's scary how bad GPS accuracy really is.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#105

Post by megous »

msiebuhr wrote: post #82
gruez wrote: post #11

Earlier quoted context omitted.

But that's client side right? What's preventing someone from implementing a GPS receiver using a SDR that doesn't have those restrictions?

Copenhagen Suborbitals has a blog-post about those limits: By default all GPS units have some built-in limits (so-called COCOM limits) that prevents them from providing any data if the velocity exceeds 515 m/s at altitudes above 18 km. These artificial limits are built into GPS receivers to prevent bad guys from using them in missiles and other nasty stuff. ... and proceed to figure out a way around ... https://copen…

> to prevent bad guys from using them in missiles and other nasty stuff

I was confused. So here's a translation: Bad guys = US enemies or non-allies. Not bad guys in any moral sense.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#106

Post by roberttod »

> In a city, the satellite’s signals reach the receiver both directly and by bouncing off of one or more buildings. The direct signal and any reflections arrive at slightly different times and if they overlap, they add up to form a sort of signal blob. The receiver is looking for the peak of that blob to fix the time of arrival.

> However, L5 signals are so brief that the reflections are unlikely to overlap with the direct signal. The receiver chip can simply ignore any signal after the first one it receives, which is the direct path.

Can someone explain this? Surely the first signal received will always be the direct signal, how could you receive signals from reflections first?

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#107

Post by piyush_soni »

mikeyouse wrote: post #30
tomlock wrote: post #29

Earlier quoted context omitted.

Apple is also an advertising company - they have unique IDs with your personal information pinned to them, and they sell ads based on your location, too.

You can change your advertising ID any time you want -- and almost none of their revenue comes from ad sales. In 2016, $190B of their $215B in sales was definitively not from ad sales, and the $25B services category that would include ad sales also includes the percentage of sales from the App Store, Apple Pay, Apple Care, iCloud.. etc. Ad sales are immaterial to their business model.

Immaterial would be a wrong word. Negligible might be better. Negligible right now would be perfect. Let's not be naive, they have a full advertisement department trying to monetize their platform and increase the revenue. They also tried to compete with Google for six years for the same, but failed in the in-app advertising. They are still trying to expand their advertising in other areas though:

http://searchengineland.com/apple-expanding-successful-searc...

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#108

Post by maxerickson »

gruez wrote: post #4

>will give the next generation of smartphones 30-centimeter accuracy instead of today’s 5-meters Didn't the US scramble the civilian signals specifically so it wouldn't be too accurate? And they're just okay with civilians having access to ultra accurate GPS receivers?

There's other constellations now, so limiting the capabilities of civilian GPS hardware has reduced strategic value.

If I understand correctly, the best implementations treat the various satellites as one combined system, rather than trying to average the solutions.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#109

Post by DiThi »

roberttod wrote: post #106

> In a city, the satellite’s signals reach the receiver both directly and by bouncing off of one or more buildings. The direct signal and any reflections arrive at slightly different times and if they overlap, they add up to form a sort of signal blob. The receiver is looking for the peak of that blob to fix the time of arrival. > However, L5 signals are so brief that the reflections are unlikely to overlap with the…

At no point it says it receives reflections first. It says that L1 signals are so long, direct and reflected signals are merged and received as a single signal.

Re: Super-Accurate GPS Chips Coming to Smartphones in 2018

#110

Post by Brotkrumen »

roberttod wrote: post #106

> In a city, the satellite’s signals reach the receiver both directly and by bouncing off of one or more buildings. The direct signal and any reflections arrive at slightly different times and if they overlap, they add up to form a sort of signal blob. The receiver is looking for the peak of that blob to fix the time of arrival. > However, L5 signals are so brief that the reflections are unlikely to overlap with the…

The key word here is "overlapping". I think the "old" L1 signal was long enough for the direct signal to arrive first, then have the reflected signal arrive while the direct signal was still being received. This would create the "signal blob".

So yes, the direct signal always arrives first, but gets messed up during receiving by the reflected signal. The L5 signal is so short, that the likelihood of reflections overlapping is reduced. Think: so short that the signal starts and finishes during the time it takes a radio wave to propagate 1 meter through air or so.

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