Author Topic: Are accurate clocks really the limiting factor in cheap Inertial Navigation?  (Read 8586 times)

0 Members and 1 Guest are viewing this topic.

Offline tomato

  • Regular Contributor
  • *
  • Posts: 206
  • Country: us

The problem is, read what you bolded. The first bottleneck. That implies that this innovation is immediately applicable and useful on its own.

I don't follow that logic.

Quote
Regardless, even if you interpret that sentence differently, the entire original article gives absolutely no hint that there's another entirely new innovation required to provide the claimed benefits. It's essentially one group claiming the credit for hypothetical future work done by someone else.

I don't see them trying to take credit for anything other than the advances they've made with small clocks.

Quote
Keep in mind that if you had a choice between getting the atomic clock in your phone OR this hypothetical quantum gyro made by someone else; based on what I'm seeing in this thread, you'd absolutely want the quantum gyro. The MEMS sensors are the first bottleneck, not the clock. Hence your bolded sentence is factually wrong.

The authors aren't trying to convert an existing iPhone to an inertial guidance device.  The MEMS sensors aren't the main bottleneck because better technology exists.
 

Offline rs20Topic starter

  • Super Contributor
  • ***
  • Posts: 2322
  • Country: au

The problem is, read what you bolded. The first bottleneck. That implies that this innovation is immediately applicable and useful on its own.

I don't follow that logic.

So what does the word "first" mean in this context then? She also says "research by our colleagues on quantum  gyroscopes should make this thing even better". If the quantum gyroscope makes it even better, then that implies that this innovation is useful on its own. If I really have to spell it out for you:
  • "Thing A improves performance by 200%. Thing B makes it even better!" <-- Second sentence makes sense.
  • "Thing A isn't immediately applicable or useful on its own. Thing B makes it even better!" <-- Second sentence makes no sense whatsoever.
Ergo, by contradiction, the sentence "Thing B makes it even better!" implies that the thing mentioned before hand is applicable or useful on its own.

Quote
Regardless, even if you interpret that sentence differently, the entire original article gives absolutely no hint that there's another entirely new innovation required to provide the claimed benefits. It's essentially one group claiming the credit for hypothetical future work done by someone else.

I don't see them trying to take credit for anything other than the advances they've made with small clocks.

Dude, they're saying "now ambulances can navigate in tunnels and we don't need satellite signals anymore". If they're not claiming the credit for those improvements, are they just rambling irrelevant BS then?

Quote
Keep in mind that if you had a choice between getting the atomic clock in your phone OR this hypothetical quantum gyro made by someone else; based on what I'm seeing in this thread, you'd absolutely want the quantum gyro. The MEMS sensors are the first bottleneck, not the clock. Hence your bolded sentence is factually wrong.

The authors aren't trying to convert an existing iPhone to an inertial guidance device.  The MEMS sensors aren't the main bottleneck because better technology exists.

So go on then, tell me a angular rate sensor that is more accurate than MEMS, and affordable and small enough to fit in a mobile phone? Answering THAT question is the FIRST bottleneck, not clocks.
« Last Edit: March 26, 2019, 03:43:52 am by rs20 »
 

Offline tomato

  • Regular Contributor
  • *
  • Posts: 206
  • Country: us
So what does the word "first" mean in this context then? She also says "research by our colleagues on quantum  gyroscopes should make this thing even better". If the quantum gyroscope makes it even better, then that implies that this innovation is useful on its own. If I really have to spell it out for you:
  • "Thing A improves performance by 200%. Thing B makes it even better!" <-- Second sentence makes sense.
  • "Thing A isn't immediately applicable or useful on its own. Thing B makes it even better!" <-- Second sentence makes no sense whatsoever.
Ergo, by contradiction, the sentence "Thing B makes it even better!" implies that the thing mentioned before hand is applicable or useful on its own.

When one states Thing A is the first bottleneck, it (generally) means there are several bottlenecks, but Thing A is presently setting the limit for performance. 

When the authors state "research by our colleagues on quantum gyroscopes should make this thing even better" it likely means that recent advances in quantum gyroscopes have improved their performance, i.e the limits imposed by the second (or third?) bottleneck has become even less of an issue.

Dude, they're saying "now ambulances can navigate in tunnels and we don't need satellite signals anymore". If they're not claiming the credit for those improvements, are they just rambling irrelevant BS then?

There is nothing in that sentence that indicates the authors are claiming credit for everything.  In fact, they have explicitly praised their colleagues for improvements in the quantum gyros.

So go on then, tell me a angular rate sensor that is more accurate than MEMS, and affordable and small enough to fit in a mobile phone? Answering THAT question is the FIRST bottleneck, not clocks.

The whole point of the article is that, with their breakthrough, the clock will no longer be the first bottleneck.  Replacing the MEMS may take over the position of first bottleneck.
 

Offline rs20Topic starter

  • Super Contributor
  • ***
  • Posts: 2322
  • Country: au
OK, but the fact appears to be that even before any of the mentioned advances, quartz crystals are NOT the bottleneck. I repeat, the clock already isn't the first bottleneck. The MEMS sensors have been the bottleneck all along.

So if you get the impression from the article that quartz crystals used to be the bottleneck, but due to their breakthrough, MEMS sensors are the new bottleneck, then you've been duped by the dishonesty of the article. It is this dishonesty, along with the implication in the original article that their advance makes satellite-less INS feasible, that I'm questioning in this thread.

I mean, looking back at the article, I see they're using words like "one step closer" in various places. So maybe my objection wouldn't hold up in a strictly technical court of law. But that doesn't make it any less slimy or clickbaity. Also, "without the need for satellite signal" is a bloody great stretch given that even the best INS's need occasional feedback, which is almost always from GPS satellites or star trackers.
 

Offline tomato

  • Regular Contributor
  • *
  • Posts: 206
  • Country: us
OK, but the fact appears to be that even before any of the mentioned advances, quartz crystals are NOT the bottleneck. I repeat, the clock already isn't the first bottleneck. The MEMS sensors have been the bottleneck all along.

So if you get the impression from the article that quartz crystals used to be the bottleneck, but due to their breakthrough, MEMS sensors are the new bottleneck, then you've been duped by the dishonesty of the article. It is this dishonesty, along with the implication in the original article that their advance makes satellite-less INS feasible, that I'm questioning in this thread.

I mean, looking back at the article, I see they're using words like "one step closer" in various places. So maybe my objection wouldn't hold up in a strictly technical court of law. But that doesn't make it any less slimy or clickbaity. Also, "without the need for satellite signal" is a bloody great stretch given that even the best INS's need occasional feedback, which is almost always from GPS satellites or star trackers.

This device involves clocks based on optical combs and accelerometers based on atom interferometers. Quartz clocks and MEMS aren't the bottlenecks -- they aren't even in the discussion. 
 

Offline rs20Topic starter

  • Super Contributor
  • ***
  • Posts: 2322
  • Country: au
Quartz clocks and MEMS aren't the bottlenecks of today's mobile phone INS systems. OK then. Lol. I guess any illusion I had that you weren't just a troll has completely evaporated at this point.
 

Offline Berni

  • Super Contributor
  • ***
  • Posts: 5050
  • Country: si
Todays mobile phones can do rough navigation without a GPS signal anyway. They use the precise time of flight measurement to the cell towers to triangulate the rough position and then refine it a bit using wifi access points. Google maintains a map of them by combining the telemetry data from phones and then feeds that map back to the phones in order to use it for triangulation.

This same system is also used to "hot start" the GPS receiver when needed. This rough location is combined with precise time and orbital data from the internet. With all of this the GPS receiver can calculate the distance to each satellite, telling it exactly where to look for a signal correlation and letting it lock on to the signal near instantly. Once it has a lock it can actually measure the distance to satellites and refine the location down to the usual GPS accuracy. This is why GPS in phones still works fine inside a car without even being on the dash or having a nice big GPS antenna that the usual standalone GPS satnavs needed.
 
The following users thanked this post: rs20

Offline tomato

  • Regular Contributor
  • *
  • Posts: 206
  • Country: us
Okay, I'll try again...

The device the authors would like to build requires very high performance components.  First, it requires an optical clock.  (A Rubidium or Cesium clock or a Hydrogen maser would not be good enough.)  Second, it requires a quantum gyroscope / atom interferometer. (A laser gyro would not be good enough.)  The performance levels of quartz clocks and MEMS are many orders of magnitude below what is required for the planned device, so they are not part of the discussion.  They are not bottlenecks for the simple reason that they can not ever be used in this device.  Which one functions as the bottleneck in a present-day mobile phone is irrelevant.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
There is a reason why part of the checklist in aviation is to verify the position of an aircraft before departure, all gates have their specific Lat Long available as cross check.  This is to verify the aircraft INS (Internal Navigation System) which does dead reckoning has a known staring point.  It will drift during the flight.  The INS is one navigation system, and it combined with radio Nav beacons and GPS.


Where was that photo taken? At first sight I guessed somewhere in SE Asia but putting those coordinates (10º 49' 06''N, 105º 54' 43''E) into Google it takes me to a rice field in South Vietnam.  I guessed the most probable error was in longitude and found Ho Chi Ming City airport at the same latitude but about 45 NM to the east.

Sign says: 105.911944°,
This page gives 106.62965,
This page gives 106.652,
Google Earth says 106.66034.
Maybe the airport is moving around?

This photo's coordinates also do not match. The longitude is off by a certain distance.

Internet sources confirm Google Earth uses WGS84 datum and aviation uses the same datum (as you would expect). I am very curious about this. Maybe some aviator can explain the discrepancy.
« Last Edit: March 26, 2019, 11:07:49 am by soldar »
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
If you have a precise clock and are allowed to look at the stars to recalibrate, than it's possible to find out the precise location.  It was a huge prize for a precise enough clock (or other method to navigate in the open sea, without following the shore line).  Many methods were presented.  One of them was looking at the star and precisely knowing the time, except there were no accurate enough clocks back then.

This is incorrect and it seems you do not understand how astronavigation works.  I am quite knowledgeable about astronav and it is quite too long and complicated to explain how it works in a short post but let us simplify and say the chronometer tells you the time at the prime meridian and the astronomical observations are an indication of the local time and the difference tells you you geographical longitude. Again, that is a huge distortion/simplification but the observations were not used to reset or calibrate the chronometer at all. That is not how it works.  If the astronomical observation was used to set or correct the chronometer then ... you wouldn't need the chronometer at all. The astronomical observation tells you local time and the chronometer tells you Greenwich time.
« Last Edit: March 26, 2019, 09:51:00 am by soldar »
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 

Offline RoGeorge

  • Super Contributor
  • ***
  • Posts: 7011
  • Country: ro
If you have a precise clock and are allowed to look at the stars to recalibrate, than it's possible to find out the precise location.  It was a huge prize for a precise enough clock (or other method to navigate in the open sea, without following the shore line).  Many methods were presented.  One of them was looking at the star and precisely knowing the time, except there were no accurate enough clocks back then.

This is incorrect and it seems you do not understand how astronavigation works.  I am quite knowledgeable about astronav and it is quite too long and complicated to explain how it works in a short post but let us simplify and say the chronometer tells you the time at the prime meridian and the astronomical observations are an indication of the local time and the difference tells you you geographical longitude. Again, that is a huge distortion/simplification but the observations were not used to reset or calibrate the chronometer at all. That is not how it works.  If the astronomical observation was used to set or correct the chronometer then ... you wouldn't need the chronometer at all. The astronomical observation tells you local time and the chronometer tells you Greenwich time.

I never said how astronavigation works, but I admit it's all my fault for not phrasing properly what I was thinking at at that moment.  I was trying to imagine an inertial navigation where the accumulated errors are reset from time to time using astronavigation.

Please let me try again the phrase you quoted:

If you have a precise clock and are allowed to look at the stars [thus calculating the position using astronavigation instead of inertial navigation in order] to recalibrate [the position and reset the errors accumulated by the inertial navigation system], than then it's possible to find out the precise location [using mostly inertial navigation, and only rarely recalibrate the position using astronavigation, assuming most of the errors will be caused by the inertial system, and not the timekeeping system].

[New paragraph, and then the link to a documentary about how precise timekeeping enabled the possibility of astronavigation at open sea].

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
Astronav does not have the precision to correct other more advanced technologies. A good navigator, with a good sextant, on a good day, on a very stable platform (not on a rolling ship), might get a fix with an error of 200 - 500 m.  Figure in bad conditions and cloudy days and it is a non-starter.
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 
The following users thanked this post: RoGeorge

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1407
A quick Google search turned up a portable cesium clock introduced by Symmetricon in 2011 that is the size of a matchbox, weights 35 grams and uses 115 mw of power. It's based on work done by NIST.

And is not as good as a decent OCXO...   lower power, maybe smaller, but not as stable.  And it is not a cesium primary reference... it is like a rubidium oscillator that uses cesium... and costs a butt load 'o bucks.
 

Offline texaspyro

  • Super Contributor
  • ***
  • Posts: 1407
I use the noise from the low order bits from a MEMS INS board accelerometer, gyro, and compass data in my true random number generator.  The output from that TRNG passes every statistical randomness test.  MEMS chips are useless for anything but low precision applications.
 

Offline hamster_nz

  • Super Contributor
  • ***
  • Posts: 2812
  • Country: nz
Call me cynical, but...

Stated problem this solves: We need a technology breakthrough to know where ambulances are in tunnels!

Proposed solution #1: We need new tech for an ultra-precise time reference to enable an ultra-precise Inertial Navigation System

Proposed solution #2: We could add a CANBUS interface to the navigation system so it can read the odometer and to deduce location when GPS signal is not present

Maybe the unstated real problem: We need equivalent GPS navigation functionality for times when the GPS system is either down, cannot be trusted, or is being denied through jamming or other Electronic Counter Measures. However we also need to attract funding.

I'm slightly surprised that they haven't also mentioned it would be useful for cave and/or mine rescues...

Gaze not into the abyss, lest you become recognized as an abyss domain expert, and they expect you keep gazing into the damn thing.
 
The following users thanked this post: rs20

Offline CatalinaWOW

  • Super Contributor
  • ***
  • Posts: 5569
  • Country: us
Call me cynical, but...

Stated problem this solves: We need a technology breakthrough to know where ambulances are in tunnels!

Proposed solution #1: We need new tech for an ultra-precise time reference to enable an ultra-precise Inertial Navigation System

Proposed solution #2: We could add a CANBUS interface to the navigation system so it can read the odometer and to deduce location when GPS signal is not present

Maybe the unstated real problem: We need equivalent GPS navigation functionality for times when the GPS system is either down, cannot be trusted, or is being denied through jamming or other Electronic Counter Measures. However we also need to attract funding.

I'm slightly surprised that they haven't also mentioned it would be useful for cave and/or mine rescues...

I just think you aren't cynical enough.  It is a three step process.

1.  I want to play in this sandbox.

2.  I am not creative enough to come up with real applications for my pet rock.

3.  Funding requires some applications, so just throw whatever I read in popular magazines and trade journals at the problem.
 
The following users thanked this post: Siwastaja

Offline tomato

  • Regular Contributor
  • *
  • Posts: 206
  • Country: us
I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place. 
 

Offline Mechatrommer

  • Super Contributor
  • ***
  • Posts: 11714
  • Country: my
  • reassessing directives...
I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place. 
any person who designed navigation related system know they want to use any possible technological advancement. the classical method is three, dead reckoning algorithm, landmark and beacon. i'm not an expert in GPS but the way i see it, it can be classified as beacon, beacon usually man made for this specific purpose. landmark as mentioned natural star formation, land features (mountains, trees, holes, building, signage etc). triangulation is beacon from comm towers, including your LORAN. dead reckon incl MEMs/INSs sensors, math, cpu and the discussed clocking system. so, nobody ridicule anything if it can help navigation, this is human's life related. except the article in OP and author writing you've highlighted with their "atomic clock buzz no GPS needed" campaign.
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Offline CatalinaWOW

  • Super Contributor
  • ***
  • Posts: 5569
  • Country: us
I was skeptical of GPS when I first heard of it.  Not because LORAN was already here.  LORAN has obvious limits, starting with coverage.  What I questioned was whether anyone less well funded than the military could deal with all those receivers and the computation in a portable package.  Fortunately I underestimated the impact of Moore's law.
 

Offline iMo

  • Super Contributor
  • ***
  • Posts: 5570
  • Country: va
The best mechanical gyroscopes (ie Sperry) did <1degree error in 1 hour, afaik. The mechanical gyroscopes provide the "attitude" to a ref frame, while the MEMS gyroscope outputs the "angular velocity". I would rather not dead recon with a MEMS based system even having atomic clock on the chip :)
« Last Edit: March 27, 2019, 08:55:29 am by imo »
Readers discretion is advised..
 

Offline hamster_nz

  • Super Contributor
  • ***
  • Posts: 2812
  • Country: nz
((( quietly hoping somebody else posts a link to today's XKCD, that I just read and LOL to )))
Gaze not into the abyss, lest you become recognized as an abyss domain expert, and they expect you keep gazing into the damn thing.
 

Offline soldar

  • Super Contributor
  • ***
  • Posts: 3595
  • Country: es
I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place.

I am not sure if you are serious or what point you might be trying to make but
(1) the capabilities of satelite navigation compared to LORAN are immensely greater. Satnav systems were first developed for missiles, submarines and surface naval ships in circumstances where LORAN could not be used.
(2) GPS did not replace LORAN but earlier satnav Transit and
(3) satnav has proven useful enough that Russia, China and the EU have all developed their own satnav systems.
« Last Edit: March 27, 2019, 12:26:22 pm by soldar »
All my posts are made with 100% recycled electrons and bare traces of grey matter.
 
The following users thanked this post: rs20

Offline RoGeorge

  • Super Contributor
  • ***
  • Posts: 7011
  • Country: ro
Indeed, the GPS system is very important because it answers the first 2 most important human questions:
1. Where am I?
2. What time is it?

Ufortunatly, it doesn't answer the 3'rd one:
3. WTF, am I doing here?
 :-DD

Offline coppice

  • Super Contributor
  • ***
  • Posts: 10031
  • Country: gb
I suspect some of you would have ridiculed the GPS system when it was proposed, since we already had a perfectly good navigation system (LORAN) in place.

I am not sure if you are serious or what point you might be trying to make but
(1) the capabilities of satelite navigation compared to LORAN are immensely greater. Satnav systems were first developed for missiles, submarines and surface naval ships in circumstances where LORAN could not be used.
(2) GPS did not replace LORAN but earlier satnav Transit and
(3) satnav has proven useful enough that Russia, China and the EU have all developed their own satnav systems.
This is post hoc reasoning. When GPS was being developed the receivers looked so large, heavy, complex and expensive it was far from obvious that it would ever be really compact and cheap. Most people assumed Loran, Decca and other existing systems would have a long life serving people who couldn't live with the drawbacks of GPS. However, just as GSM was developed to be a car telephone system until around 2000, yet resulted in light handhelds in the early 1990s, GPS moved far quicker than most people expected.
 

Offline rs20Topic starter

  • Super Contributor
  • ***
  • Posts: 2322
  • Country: au
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf