5 ms·
All satellite nagivation systems are trivially jammable. They use DSSS to spread out codes and resist jamming but signal levels are still so weak at the surface
by thermodynthrway 8y ago
All satellite nagivation systems are trivially jammable. They use DSSS to spread out codes and resist jamming but signal levels are still so weak at the surface it's trivial to block.
Most phones are compatible with GPS(US) +Galileo(Europe)+Glonass(Russia). Most of them also report which constellation the locks are from. GPS status and toolbox on android is a fun way to see what you're connected to.
What we need, and will probably get soon, is inertial guidance based on laser ring or fibre optic gyros in mobiles. You get a location fix every week or so and it starts out much more accurate than gps.
The US system was first by maybe a decade or more so support is nearly universal. The other systems are largely copycat, purposely compatible with existing GPS receivers.
That's why it seems like we're relying on the US for GPS, they invented it and had a full constellation in orbit before anyone else even thought of it.
Of course we're on the internet which was also invented by the US govt so I'm not so surprised why
"the backups for this backbone of the global economy have to be American" in reference to GPS at least
- maym86 8y ago> What we need, and will probably get soon, is inertial guidance based on laser ring or fibre optic gyros in mobiles. You get a location fix every week or so and it starts out much more accurate than gps. Corrections every week? This isn't possible given the drift rates of high end FOG or Lazer ring IMUs. A high-end marine-grade INS can cost over 1 million dollars. These systems will typically provide un-aided navigation solution drifts that are less than 1.8 km per day. This means that if the device were left stationary for one day, due to slight errors in the sensors and imperfect sensor calibrations, after integrating the position solution, the calculated position after one day would be 1800 meters away from the sensors actual position. With ones that you can affordably put in a phone within minutes the drift will be huge. You need something to regularly correct for the drift and currently this is GPS.
- thermodynthrway 8y agoFibre optic gyros can be miniturized to millimeter dimension, if it wasn't for ITAR. High end civilian IMU's typically use mechanical gyros which have been obsolete for decades. Also, a phone isn't typically moving constantly like the oceans so error rates would be lower.
- maym86 8y agoThis is drift for a "static" million dollar marine grade (i.e. highest grade we currently have) INS not in the ocean or moving. Drift is measured in non-moving conditions. These are the fiber optic and laser sytems you are referring to. Even if we could make that cheap and small enough it would still need regular corrections far more frequently than a week to be as good as a GPS is now.
- thermodynthrway 8y agoYou might be right but I have doubts. Most weapons are INS guided despite the long fly times of cruise missiles etc. ITAR has a massive chilling effect on development, I wouldn't be surprised if we had error rates of less than a meter a day in mobiles if development wasn't severely curtailed
- azernik 8y agoCruise missiles combine (using Tomahawk as an example) GPS, visual terrain-matching, radar terrain-matching, and INS. Because they know INS needs those constant corrections.
- wahern 8y agohttps://en.wikipedia.org/wiki/TERCOM https://en.wikipedia.org/wiki/TERCOM
- ohazi 8y agoDrift is over a given time, not distance. Missiles generally have an very short fly time, even if they're going really far.
- azernik 8y agoCruise missiles are very different from (quasi-)ballistic or anti-aircraft missiles - they fly at subsonic speeds at low altitudes (usually using a turbojet) to avoid interception. For example, the classic Tomahawk flies at ~900km/h, with the long-range variants having a range of 2500km, giving a maximum flight time on the order of hours, and so a pure INS drift on the order of low hundreds of meters.
- kqr 8y agoSo this is why my smartwatch can tell me my speed before it has a GPS lock, including indoors? Very cool! But of course, as you say, the reports of my absolute position are very inaccurate.
- deleted 8y ago[deleted]
- maym86 8y agoVelocity can come from dopplar shift of the GPS carrier frequencies. This is very accurate. An IMU can be used for walking speed estimation but it won't be as accurate using a human gait model or direct integration.
- TickleSteve 8y agoNo, any position-solution produced before a GPS lock will be due to the approximation produced by either using the last-known position or the cell-tower triangulation. That information is also used as a seed for the GPS lock to speed up the time-to-fix.
- deleted 8y ago[deleted]
- monort 8y agoAccording to the paper, one nautical mile per day was state of the art in 2006. They are shooting for one mile/month now https://link.springer.com/article/10.1134/S207510871401009X https://link.springer.com/article/10.1134/S207510871401009X
- maym86 8y agoThanks I'm interested to take a look in detail. From the abstract > In 2006, we presented at DGON symposium in Stuttgart [2] the design and navigation results of MARINS, the first FOG-based navigation system within the class of 1 nautical mile per day. This navigation system in now in production... > have we reached the limits of the technology or can we still improve the performance of our sensors? > Of course, the present FOG design is not good enough for the required performance, even in a strictly controlled environment. This is a discussion of how it could be improved not what is available in production and certainly not close to being available within a phone - which was the original point.
- cryptonector 8y agoPlus the gyros would have to be powered at all times -- that's not gonna work on mobiles.
- TeMPOraL 8y ago> What we need, and will probably get soon, is inertial guidance based on laser ring or fibre optic gyros in mobiles. Isn't this precisely how accelerometers/gyros in mobiles work?
- 05 8y agohttps://en.wikipedia.org/wiki/Microelectromechanical_systems https://en.wikipedia.org/wiki/Microelectromechanical_systems
- TeMPOraL 8y agoThanks! I didn't know about those. For some reason I was convinced phone gyros use light interference in a spiral of optic fiber. Probably because I read about that design when I was looking how solid-state gyros in RC models work.
- growlist 8y agoThere were predecessors to GPS: https://en.m.wikipedia.org/wiki/Gee_(navigation) https://en.m.wikipedia.org/wiki/Gee_(navigation)
- cptskippy 8y ago> Most phones are compatible with... Galileo(Europe) The system only went live in 2016. It's only been supported by Apple since the iPhone 6s, and Samsung has supported since the S8. I would be hesitant to say that most phones are compatible. In 2016 most of the flagship phones had support but even having a compatible SoC doesn't mean it was implemented. The Google Pixel was released in 2016 with a Snapdragon 821 that is compatible yet the Pixel does not support Galileo.