Ionospheric Interference With GPS Signals 127
Roland Piquepaille writes "In recent years, we have become increasingly dependent on applications using the Global Positioning System, such as railway control, highway traffic management, emergency response, and commercial aviation. But the American Geophysical Union warns us that we can't always trust our GPS gadgets because 'electrical activity in the... ionosphere can tamper with signals from GPS satellites.' However, new research studies are under way and 'may lead to regional predictions of reduced GPS reliability and accuracy.'" Roland's blog has useful links and a summary of a free introduction, up at the AGU site, to a special edition of the journal Space Weather with seven articles (not free) regarding ionospheric effects on GPS.
Time to declare war? (Score:5, Funny)
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They are not terrorists, they are the result of the cold war superpower arms race.
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Yeah, and there is some speculation that large-scale structure in the universe is actually governed by electric and magnetic influences, rather than gravity.
There have been nuclea
Oblig. (Score:3, Funny)
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Indeed, my conspiracy theorist friend, indeed [wikipedia.org]
Dual Frequency (Score:5, Interesting)
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Re:Dual Frequency (Score:4, Informative)
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Also, it looks like military personnel ended up buying there own civilian units a large percentage of the time with obvious problems.
Looks like it was officially disabled around 2000 or so.
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Wikipedia [wikipedia.org] agrees with you. The main problem with error injection was the proliferation of commercial-grade GPS receivers among military personnel: the US Army couldn't afford to equip everyone with a military-grade receiver, so the soldiers started buying them themselves.
And if I'm not mistaken, they were considering to enable it again, but the FAA asked them not to, since aircraft use it to better state their position (I'm sorry for any factual inaccuracy, but I'm just a Spaniard with a limited understa
Re:Dual Frequency (Score:5, Interesting)
That's not to say that it was a total piece of shit. It was water-proof and pretty durable. It was really extensible; it could be plugged into a variety of other things, which made them really useful *if* you had the proper hardware. The problem was that all the needed gear to take full advantage of it required a vehicle to transport and provide power. The PLGR was a fantastic piece of gear for anyone but the infantry. Problem is, there's a hell of a lot more infantry that needs coordination on the ground than there is anyone else. So, many of us bought our own.
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Less positioning, more navigation. GPS is rapidly becoming (if it hasn't already) a level 1 navigational device (trustable on its own). Right now, it's level 2, which means it's good for general use, but must be com
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The WAAS satellites are not GPS satellites. First off the WAAS sats ar
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Ionosphere interference is reduced by using two frequencies. The higher frequency shifts less when it enters the ionosphere. Both frequencies are compared by the receive
Re:Dual Frequency - Not just for the military (Score:1)
Not something you'll find in your Garmin or iPhone 3G, but not horrible uncommon in high-end survey equipment.
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Good Grief! (Score:4, Interesting)
Re:Good Grief! (Score:5, Interesting)
Re:Good Grief! (Score:5, Interesting)
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Blackmail (Score:2)
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Submit your own super-interesting stories if you have better ones.
Re:Good Grief! (Score:5, Interesting)
Roland has an extremely high ratio of postings and a *much* higher ratio of accepted postings. So much higher that for the longest time I figured he was a sockpuppet for one of the
The discrepancy is too large to be ignored or brushed under the carpet.
After all, the
The standards that most postings are held to would mean that *none* of Rolands postings would have been accepted, they are the very definition of blog spam.
Something is smelly here, even if I can't quite put my finger on it. Maybe it's time to do some scripting to get some real hard stats on this whole thing.
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Let me spell it out for you, I'll ignore your strawman about me not liking him 'because he's french', I don't know what prompted you to say that, it lowers the discussion level:
I wasn't trying to troll - I just couldn't think of any other reasons off the top of my head. :)
However, I must say that I don't spend a lot of time analysing the balance of quality of stories to the chance of them being accepted, so I'll have to defer to your superiour knowledge in this area
I just look at the stories, and see if I like them. I happen to be a Radio Ham, so this one is of interest to me.
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I don't like him becasue he plagiarises stories from other sites, copies them to his blog, then submits to Slashdot. He's just trying, and succeeding, in pumping up his pagerank. Originally he used to ONLY link to his blog. There were many complaints about that, eventually he started also giving the original link, but he always adds his blog link as well. He's a parasite.
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However - why shouldn't he get a little PR for supplying Slashdot with stories?
After all, we'd be moaning in hours if there weren't any stories posted.
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Every submitter gets one link, on his name. He pimps his site with the bogus "for more information" one he puts at the end (in this case the slashdot editors have, unusually, added the original link, if you compare with the firehose version.
Anyway, it's a bit like RealNetworks, there is a lot of residual mistrust after seeing how they exploited their access, and a feeling not to trust them an inch again.
After all, we'd be
Re:Good Grief! (Score:5, Funny)
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I don't want to make the Roland here, but what's your problem with Roland Pick-a-pie?
I guess Roland is just a new name for that entity Anonymous Coward that we all love and respect for its valuable contributions to our beloved slashdot. What would a day on slashdot be without goatse, first post and Roland postings
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But at least you knew the transmission was scrambled since the data failed to align with the required protocol (e.g. a bad checksum, no magic number, etc.). I think this is what the OP was referring to. If you can get any data from the transmission after the signal has been processed, it's highly likely that its good data.
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If you can get any data from the transmission after the signal has been processed, it's highly likely that its good data.
The real problem isn't so much distortion of the signal in the ionosphere, which seems to be what you are getting at. The problem is that variations in the ionosphere change how long it takes for signals to get through the ionosphere. This is obviously a problem for GPS since it relies on timing the signals in order to calculate positions.
Re:GPS is digital! (Score:4, Insightful)
The ionosphere can change rapidly (Score:1)
For those who don't know how the ionosphere affects GPS, here's a quote from one of the articles tfa links to:
Re:GPS is digital! (Score:5, Interesting)
So you might hear the tune fine, but if the ionosphere delays the tune every so slightly, your reading will be off and your position will be inaccurate.
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http://en.wikipedia.org/wiki/Differential_GPS [wikipedia.org]
http://en.wikipedia.org/wiki/Waas [wikipedia.org]
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Aviation can go both ways, but planes do come with altimeters.
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one will be where you are, and one will be up or down from where you are.
This is not completely accurate: It's enough to say "the other one will be up". It will be somewhere on the other side of the satellite's orbit, like a mirror of your real position on earth.
The GPS receiver do not need to pick the most likely location of the two. Because it does not really calculate positions at all. It calculates your *new* position, based on an assumed position (which it updates every time it calculates a new position). This is why a cold start of a receiver can take a long time.
Anyway.
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If you know your distance to one sat, and you know that sat's location, you can draw a mental sphere with radius your_distance around it. You must be somewhere on that sphere.
Now, if you know your distance (and location of) of another sat, you have another sphere where you can be on. Obviously, you cannot be in two places at the same time. So the intersection of those spheres must be where you are.
The problem is this: Intersect two spheres and you get a circle! You can be on any s
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Interestingly enough, also, you need to take relativistic distortion into account. General relativity speeds up the atomic clocks (due to less gravity) and special relativity slows down the clocks (due to their velocity); add them together, and the clocks run about 28 microseconds slower than they would sitting beside you on Earth.
Trilateration, not triangulation (Score:1)
Re:GPS is digital! (Score:5, Informative)
Just receiving a digital signal doesn't mean its right!
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Why not just calculate based on the reported velocity of the vehicle, 'pinging' satellites every minute or so and simply dropping anything that puts you in Antarctica?
Trains? Anything that puts a train a certain distance off the track could be dropped. The acceptable values would have to be manually defined, however. Results could also be checked against reports from evenly-spaced receiver towers, with each train constantly broa
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Why not just calculate based on the reported velocity of the vehicle, 'pinging' satellites every minute or so and simply dropping anything that puts you in Antarctica?
Because that is not what happens. TFA (and the F does _not_ stand for "fine" in this case) claims that "your GPS cannot be trusted". It can. Ionospheric interference has been well known since the initial design of GPS. It is one of several factors that introduce a few meters of inaccuracy into the GPS in your TomTom, and all these factors add up to about ten meters of inaccuracy. It doesn't put you into Antarctica - and since your GPS calculates a four-dimensional position (x, y, z and time), the chances t
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What about timekeeping? (Score:1, Interesting)
My understanding is that you need to see a constellation of 4 sattelites to get accurate time. Use 3 to pinpoint your exact position, and then use that knowledge, and your knowledge of the 4th sattelite's position, to compensate for the delay in receiving the time signal.
If the precision of your position lock is degrated or unreliable, would the decreased precision of the reference time be enough to cause problems?
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If you absolutely need it, survey exactly where your receiver's location is, and use that to figure out the time offset. Of course, the more satellites, the better, but degradation won't be as much an issue. But if you're putting your receiver in a place with very limited sky, you may need to reassess your options.
However, if you're a Ham.... (Score:5, Interesting)
I check the "Space dials [rice.edu]" regularly, and can't wait for them to be in the red! 73s.
This could be dangerous ... (Score:1)
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What *IS* new is that scientists are using this GPS inaccuracy to map the ionosphere.
Mid-latitudes (Score:1)
second amendment (Score:2, Funny)
Fortunately we have the right to bear sextants.
Now which button on this Tom Tom gives me the GHA of the first point of aries?
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Aviation uses RAIM (Score:1)
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No Problems for me... (Score:4, Insightful)
Doesn't cause any problems for me. Sometimes I've got just a few feet of accuracy in my position, other times it's 10's of feet. I guess it would cause issues with my home-made cruise missle, though...
Aviation has used VOR navigation for decades, developed during WWII. And the US Government has a big OFF switch for that, too. Part of pilot training is knowing how to navigate when all the fancy gadgets are offline. Because you never know when a system will fail.
I just view this as a confirmation of what I've noticed before: that sometimes the signals aren't as good as others. Fortunately, I have a computer that is capable of recognizing the situation and performing the necessary error correction on the fly. I call it my brain.
Hence WAAS (Score:3, Insightful)
In geocaching, the greater the accuracy the better. For car navigation, you don't even need it, as the accuracy is better than the width of a road regardless!
This article seems to be a decade behind... -Randy
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Re:Lane Level Accuracy (Score:1)
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How do you know if you are in an exit/turn lane? On a service road parallel to a freeway? In a lane with a stalled car ahead?
By looking out the window? ;-)
Seriously, though, don't forget that the signal received by your automotive/handheld GPS unit is not the only source of error when trying to orient yourself in relation to an object. Your maps have to be incredibly accurate, too.
Most of the consumer grade mapping solutions available for automotive GPS usage are only accurate down to a certain point- in my experience this is anywhere from 30-150 feet for Garmin's City Navigator series of maps. Some of their older map products can be much worse (some topo software was scaled off of paper maps, for example, and only claims to be accurate to within 800 feet). I too am an avid geocacher, and when a cache hider sloppily takes an inaccurate waypoint, it doesn't matter how accurate the signal is for you, you'll be off.
Now, imagine the best case scenario, where your lane data is accurate to within 10 feet and your GPS unit reports 10 feet accuracy (I've seen my 60Csx report as low as 6 feet, but that's dubious). Combine your error with the map error, and you could be as much as 20 feet off- making it difficult for the GPS unit to be certain as to which 16-foot-wide lane you are in.
Everything I've ever read about lane-level accuracy involves embedded sensors in the roadway (RFID, perhaps?) to pinpoint your position.
Some simple facts about space weather (Score:1)
The ionosphere causes several effects (Score:1, Informative)
There are two major ionospheric effects: delay and phase variations. The ionosphere is a region above the earth's atmosphere in the altitude range from about 200 km to a few thousand km. In this region there is a very low density of atoms and a significant fraction are ionized by solar radiation. The presence of electrons, combined with the earth's magnetic field, has a significant e
GPS designers already working on this (Score:2)
LORAN - still in use. (Score:1)
With SBAS, yes you can!! (Score:1)
Differential GPS (Score:2)
For various reasons (including this one), people have come up with ways to enhance the accuracy of GPS.
I've used differential GPS for several applications. Terrestrial beacon stations listen to GPS, and compare where they know they are with where GPS says they are. They broadcast these corrections and anybody in the vicinity can use them.
WAAS is a similar concept. I've played with it too.
...laura
Roland the Plogger, again (Score:3, Informative)
First, it's a Roland the Plogger story, so it's going to be wrong.
GPS accuracy is a serious problem for users who need high precision. More applications are assuming that GPS is precise to a few meters, which, often, it isn't. It's always good enough if you just need to find an airport. Below that level, error can be a problem.
Local high-precision systems, like GPS-based systems for landing, use a pseudolite, a receiver on the ground in a known location that receives GPS and broadcasts small corrections. The pseudolite is usually located near the end of the active runway, so as aircraft get closer to the runway, the error approaches zero. There's a similar setup for "precision farming", where the tractor precision is precisely known but there's a psuedolite at the side of the field.
Without a pseudolite, it's harder. Part of the problem is that there aren't enough satellites. To get a GPS lat/long fix, you need to see at least three sats. To get lat/log/elevation, you need to see four. For high-precision work (down to 15cm), you need five, plus correction signals from receiving stations (see Omnistar) that are monitoring propagation. You're lucky to see four in a built-up area, because you can only see part of the sky. If you can see five, you can measure error. Some systems use both GPS and GLONASS sats; now that Russia is building up the GLONASS constellation again, this works better. By 2009, the GLONASS constellation should be fully populated, and systems that use both GPS and GLONASS will have a better chance of seeing five sats.
Propagation problems always add delay; they never subtract from it. Propagation problems come from what the ionosphere is doing, and from reflections from big metal surfaces like buildings. In urban canyons, you're seeing mostly bounces.
This is an issue for civilian uses that assume the system has more precision than it really does. Car navigation systems that try to tell whether a car is on a freeway or an adjacent side street from GPS data alone are likely to have problems. The same problem applies to GPS systems for railroad signalling (these make me nervous) which try to tell on which track a train is running.
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This is a misleading statement, because it depends on the model of receiver you're using. Some newer receivers, for example, use the two GPS signals -- military and civilian -- to resolve ionospheric interference. You don't actually need to decrypt the military signal, you just have to be able to receive it. Then the receiver can adjust for the ionosphere's activity and give you a highly accurate signal.
l2 is the solution (Score:2)
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Not sure either if the L1/L2 frequency shift alone will counter all affects.
(Actually not noticed a significant difference on our keyed/unkeyed gps receivers in the lab - all of which have the same signal feed (gps amplifier/repeater feeding the rf to each PLGR) since the SA was reduced to effectively 0 a few years ago.)
railway control? (Score:3, Funny)
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I mean, you could say the same thing about cars- they mostly just stay on the road, right?
-b
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The difference between signal and noise (Score:2)
The cool part of this article is that scientists are now using GPS receivers (cheap, ubiquitous) to study events in the ionosphere, which used to require fixed ground-based ionosondes or worse yet sounding rockets.
I bet an upper atmosphere nuke test would be bad (Score:1)
not that bad a problem with newer GPSr (Score:2)
I'm not sure this problem is as big as it's made out to be.
Duh. (Score:2)
You know what this mean... (Score:1)
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