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Ask Dr. Ramsey Faragher About Navigation/Positioning Technology
Dr. Ramsey Faragher graduated from the University of Cambridge in 2004 with a first-class degree in Experimental and Theoretical Physics. He then completed a PhD in 2007 at Cambridge in Opportunistic Radio Positioning under the direction of Dr. Peter Duffett-Smith, a world expert in this field. He is now a Principal Scientist at the BAE Systems Advanced Technology Centre specializing in positioning, navigation, sensor fusion and remote sensing technologies in the land, air, sea and space domains. We recently covered his NAVSOP project, an advanced positioning system that exploits existing transmissions such as Wi-Fi, TV, radio and mobile phone signals, to calculate the user’s location to within a few meters. Dr. Faragher has graciously agreed to answer any questions you may have about NAVSOP, the future of GPS, or what a theoretical physicist puts on his business card. Ask as many questions as you like, but please confine your questions to one per post.
He seems to have written a post on how this works and then later made an account. Sorta verified here. His post is very informative and might answer a lot of questions and generate more meaningful ones.
My work here is dung.
Has this been tested in remote areas? For example, middle of the ocean, Saharan Desert, Antarctica?
sudo make me a sandwich
I'd imagine a lot of positioning calculations involve accounting for or adjusting for known effects or noise. For example, accounting for general relativity in GPS. What is the most surprising correction you've ever come across (even on an exam or done in theory)? Have you ever found yourself saying "I didn't think that could affect the calculations so much."
My work here is dung.
What kind of accuracy is possible to achieve using NAVSOP - or other systems you know of - if I can place stuff like APs, mobile phones, etc. myself in a factory area? Do you have methodology for designing placement of such devices so positioning accuracy is reached at every point? How low can one get with costs of such solutions?
Will there ever be a way to accurately use GPS without open sky access in a building or underground?
It would seem that to use this technology, the client would need to have a much larger datastore than with GPS: Whereas only the positions of the GPS satellites need to be known to make a calculation, the dataset here is in the many thousands to millions. In addition to the data required for map storage, it would seem any implimentation of this would require an internet connection to download the data in a geographically-restricted fashion. This opens the door to privacy issues that standalone GPS clients do not have.
How do you plan on addressing the privacy issue with your product?
#fuckbeta #iamslashdot #dicemustdie
Any chance of development kits being released in the near future? Indoor localization is a very tricky problem, and if I can just use somebody else's chip/SDK/setup, then I'd prefer to go that route.
Something that surprises me is that we're so obsessed with the exact positioning of things on Earth but at great exo-solar distances, we seem to be okay with measurements to the nearest million light years. A couple days ago I read about a new method devised to measure location to within a few hundred meters of something 200 million kilometers away from Earth and it struck me as odd that more effort isn't put into this. While the practicality of Earthbound work is far greater, the implications for physics and verifying theories seems to be an obvious benefit for better positional measurements in space. I know satellites and objects near Earth are heavily measured but why isn't there more attention paid to precision of deep space objects? What problems prevent sensor fusion from being applied to space? Too much noise? No way to actually verify your results?
My work here is dung.
With the improvement, both in time and coverage, that using WiFi and cell tower triangulation adds to straight GPS or A-GPS, and with NAVSOP going even further, what signals (or aspects thereof), in the EM spectrum or otherwise, remain untapped? What's the next step in improving time, coverage, energy efficiency, affordability of location systems?
How much of this can be done automatically and how much of this must be hand guided? For example you talked about fingerprints changing over time and being used only as a guide. Is there a measurement or confidence variable that you can employ to automate when the fingerprint is still valid or has morphed too much? Or is that something that a human overlord must monitor and do research to notice that a new apartment building has just been opened and there are now hundreds of new signals? It feels like you are using an open domain that could have outliers and irregularities that require a human to clean the data before it can be trusted to give you low false positives and true negatives. What statistical methods do you use to overcome these sort of real world problems so that your system can be put anywhere and work?
My work here is dung.
Hi, Dr Ramsey!
What is your best estimate as to what is the US DOD's current GPS backup system?
IIRC Obama cut the budget for LORAN around 2010 and till then the system was financed with the explicit explanation and purpose - GPS backup. But no more...
I am currently teaching ECDIS systems to mariners and I always emphasize the weaknesses of GPS under jamming. Ever since Selective Availability has been switched off, the jamming topic pops up more and more as a soft spot of the whole process, so I think we are not fooling ourselves that the US would let down such a gaping hole in its systems uncovered...
Now, Make Your WISE Move...
Why does this news story read like a resume?
Does your system record data so that the position data can be enhanced with Post Processing?
I have seen a description of the new Sirfstar V chips doing much the same as you describe. As they are also in the vicinity of Cambridge, is there some cross-pollination of ideas here, or is theirs a completely separate system?
Wouldn't this thing require a whole slew of regulatory approvals since you'd be fishing for different types of signals? Or would this involve mere processing of data already available to, say, the smartphone armed with this technology?
People have used opportunistic radio transmissions to navigate since the beginning of radio. For instance, the Japanese used civilian radio stations to navigate their way to Pearl Harbor.
Back in the day ...
Radio stations could be asked to go off the air. Radio Amateurs would be asked to turn in their transmitter tubes. It was relatively easy to create radio silence.
Now it is probably impossible to create radio silence. The terrorists don't need GPS to guide their drones to their targets.
I would like to buy a few devices similar to a WiFi Router that would allow GPS recivers within the confines of my house to have 12 inches or less accuracy. This would be great for interfacing to my phone for home automation like things. Or for house vacumes that are very accurate. Is anyone working on single building high resolution positioning?
How do we move in relation to the colonthree? :3
Would the individual recivers for NAVSOP be linked to each (either remotely or on an ad-hoc basis) in order to better improve the tracking? If so would you be able to model "swarming" of users for modeling of travel patterns?
Don't want to sound like a prick, but might be cheaper and more effective to devise a star/sun fixer with a chronometer, a compass, and a star database (like they did for a few hundred years on ships, and still do, but manually with a sextant).
Of course you're screwed if it's cloudy and you can't sight the stars.
Global positioning signals are used to help target various weapon systems in the United States arsenal. These signals can be--and have been--spoofed, to mis-direct these devices. Do you see spoofing technology as a meaningful threat to our offensive and defensive capabilities?
How accurate could GPS get? Will it be possible to make GPS accurate down to submeter levels? Could we one day get GPS accurate to within centimeters or better?
Does the gravitational field strength could be used also for NAVSOP ?
Maybe slight natural variations, and buildings, underground structures like metro, subways, large sewers can be sensed by gravitational sensors, at least the new ones with atom waves interference...
Can you please tell me the whereabouts of Carmen San Diego and/or Waldo?
The Kruger Dunning explains most post on
I recently drove from Florida to North Carolina and for a significant amount of time received errors about being unable to find GPS signal. What would it take to improve our GPS coverage.
Dr.: I find science and technology to be endlessly fascinating areas of study, but I know that I am in the vast minority in society in this respect. What do you wish more people understood or appreciated about the science and technology underlying what you do?
Are there other frequencies of EM radiation that would be better suited for navigation than the gigahertz used now?
What is your favorite map projection? (Geeks like to know these things)
How interoperable are the European and American GPS systems?
Might I ask your favourite pub in Cambridge and the local area? It doesn't need to still exist.
What potential do you see in the combination of these "opportunity" signals (Wifi etc.) that are to be used in NAVSOP and data from sensors like an air-pressure sensor, accelerometers etc.?
We all know how GPS works, and even the basics of the math behind it, but where does one find more in-depth mateirals? Like if one were to create a GPS receiver, how to translate those signals into something useful? Not just dumping the equations out and say "solve this" but working step by step through a solution and then adding in corrections like relativity?
So, since the GPS satellites and other systems are enmeshing the world in streams of digital data, can a portion of the data stream be used to transmit some sort of key so that it can be proven the receiver was at a specific space-time coordinate?
Like if satellite A was transmitting a continuously varying stream of random numbers and satellite B was doing the same then a receiver could take the product of the "random" numbers that it captured over a short window of time and use it to encrypt and "space-time" stamp it (neat concept, can I patent it?).
If the flow of numbers is sufficiently fast perhaps it would be impractical for a third party to retain and compare all possible products of the numbers sent by all the satellites. (Maybe it'll need another source if random numbers to mix in, say from a natural source like a pulsar?). Then again since I'm not a cryptographer/signal specialist perhaps there is a very simple reason why this won't work.
Years ago during world war 2, pilots flying at night used dead reckoning, and followed two other signals, one from the north of England, and one from the south of England. One was called cat, and the other mouse. Cat chased mouse. Hyperbolic curves plotted on maps meant that when the signals were a certain distance apart, you were a certain distance from them (and using loop antennas gave a rough direction to each, given that the signal is strongest when the antenna is orthogonal to the EM radiation). It eventually became LORAN. HF radio direction finding usually involves "ELEPHANTS CAGES" like Pusher HF-DF Wullenweber "BULLSEYE" antennas, etc. These are very large because of the physics involved. To keep your unit small, how do you get around these challenges? Can you use HF frequencies or are you limited to VHF/UHF? I ask because the range of some of these signals (WIFI) is very small, cell phone signals are likewise less than 20 miles, TV is good for about 50 miles. When you are at sea, on the sea, unless you get backscattering, you don't get any of these (and the frequencies are too high to refract on the ionisphere, ie no 'skip'). HF will refract, but then we are talking about physics and size. An aircraft can get signals from much further, but you would still rely on a lot of dead reckoning over much of the worlds oceans.
In order to combine all the sources of information, are you relying on a messy approach, something based on many signature machine learning algorithms (think boosting, SVNs, random forests etc) or are you writing an explicit generative model for the noise and then applying filtering to it, with a particle filter for instance?
\u262D = \u5350
So I've heard that a problem with the GPS and presumably other systems is that the radio signals are slowed by varying amounts by going through the ionosphere (thus reducing accuracy). I realize that you cannot use quantum entanglement to send (new?) information but does that include the information that a measurement has been made (if not the result)?
So could GPS use entanglement to precisely determine the time of a measurement? I think it's been demonstrated that they can send an entangled photon hundreds of kilometers so it's only a matter of time before it becomes practical to use these devices on satellites.
Following the downing of an American drone in Iran the hypothesis was put forward that the Iranians spoofed the GPS signal and convinced the drone that it wasn't where it thought it was in order to get it to land in Iran (I'm not sure if this was ever confirmed). A recent issue of Aviation Week reported on a group I believe in the U.S. working on the same idea, spoofing the GPS signal in a transparent manner to convince an autonomous vehicle that is was somewhere other than its actual location. Would NAVSOP make it more difficult to accomplish this sort of spoofing?
Seems like a great alternative to GPS in most casual situations, or as an addition to it for faster position locks while driving.
The questions I have are:
1) As technology changes, such as the changing of the cell phone signals to differing frequencies as they increase speed.. ie, 4g, LTE,...etc or OTA TV switching to digital.. Will this still work? Or would people have to replace their "non gps navigation unit" when various signals that this relies on for positioning stop, or change frequencies? We've seen a lot of changes already so we know that things can change very rapidly and perhaps in unexpected directions.
2) What about countries or certain places that don't have the same infrastructure as the US or most of Europe? Or very remote places such as in the middle of a Rainforest (whichever one). Gps would work there as long as you had open view to the sky, but are there enough signals bouncing around (I guess I should say Signal Propagation?) even there for this technology to accurately and (hopefully quickly) give a location?
3) Any, plans perhaps as I mentioned above, on possibly merging the technology with gps as an adjuct instead of as a full on replacement? I think this would be a great boon for mobile navigation, perhaps even saving serious battery life in mobile devices. It could supplement location information when a gps signal becomes weak or sporadically drops in and out (due to the weather or obstructions like bridges, tunnels, big city buildings) keeping the phone from having to boost power to try and find/maintain a gps signal. This would save considerable power and allow navigation to continue until a strong gps lock can be made at lower power levels.
He's a PhD and expert in a technical field who is sharing his expertise in that field, and you, Mr. Coward, are asking what value he brings to /.?
MCSE? No, sir...I don't do Windows. Yes, I am an idealist. What's your point?
So I seem to remember a proposal to use pulsars to provide a sort of galactic GPS. (Pulsars, spinning neutron stars, are extremely stable periodic emitters of radio waves at interstellar distances). I think this might be what an earlier poster was referring to for spacecraft navigation, I believe they were used on the famous Pioneer 10 plaque (with the naked humans) to show aliens where we live.
Anyway, what's the accuracy for this (the previous poster mentions several hundred meters over hundreds of kilometers but I don't know if it's the same system)? Is it as good as (terrestrial) GPS? Will it be good enough to use for the upcoming GAIA mission which will map the 3D location of a billion stars in our galaxy?* (The positioning requirements of that mission are borderline insane!). Is there any way to use these celestial beacons as (another) GPS backup or are the signals far too weak (or unstable or blocked by our atmosphere or are in already used radio bands)?
Sorry about the more than one questions but they're all related. :)
*actually since most (all?) of these pulsars are within our galaxy maybe they are not far enough away to have no apparent motion (in which case they would be hard for GAIA to use as a reference). Are there any extra-galactic sources (Quasars?) that could serve a similar function?
Was there really no solution to the interference of Lightsquared's product with GPS devices?
Why is it that we can't manually calibrate current GPS devices against known valid position data for better accuracy?
I have been to various benchmarks and have been able enter the correct altitude and it remains stable for a very shot time but am unable to correct for lat/lon differences.
Time to offend someone
Dr. Ramsey,
In your post on Monday, you said:
A lot of the "this is not new" comments refer to differential positioning using reference receivers and having access to databases of transmitter locations (Rosum, the old Cursor positioning system from Cambridge Positioning Systems, etc). We consider those aspects to be undesirable constraints on a flexible opportunistic positioning system and don't rely on them.
Is the idea to be a fully self contained (and self teaching) system? Is there any way to (reliably) share transmitter location data between clients using some sort of P2P or swarm connection?
Ceci n'est pas un sig.
Could your technology be augmented to enable bistatic radar apps for our mobile phones?
Have you considered doing the same using earths magnetic field rather than RF? Local varience within buildings or geology, earth field lines or using a RLG/GPS reference to see parallax in declination as a basis for rough positioning?
How do you see trust being handled in these systems? It would seem to beat the core of everything - anti-spoofing, error detection and correction, and possibly authorized receivers.
John
Would it be possible to get a more accurate location data from GPS by using multiple receivers separated by some relatively close, aproximatly 1 meter, known distance and then averaging the returned position to get a more accurate center position?
I am envisioning something that uses 4 or 5 receives arranged in either a triangle or square with one receiver located in the center of the others. The distance between any 2 of the receivers would be at most slightly more than 1 meter which is below the accuracy of civilian GPS. From my past experience in using 2 handheld GPSes (one in each hand) it seems like this would be reasonable and would produce better results than using a single device.
Time to offend someone
I found it striking that in the case of the drone that was forced down in Iran (e.g.) the 'return to base' failsafe seemed to be completely dependent on electronic signals.
It would seem much harder to spoof the position of the sun, the Earth's magnetic field, the position of the stars, etc. I presume, perhaps naively, that the sensors and algorithms to do this wouldn't be all that expensive or complex. What's the challenge in getting computers to use traditional navigation techniques?
My God, it's Full of Source!
OUTSIDE_IP=$(dig +short my.ip @outsideip.net)
What would you recommend for a real time low cost small size light weight position/speed sensor that could be used for the sport of racing homing pigeons? I'm not talking about a data logger, but a practical device that can transmit information to allow for remote real time information delivery.
My question is rising off the ashes of the LightSquared fiasco. One key issue that LightSquared could not overcome is the reality of the receive side selectivity of existing GPS receivers. To my understanding, going forward, the FCC envisions to enforce stricter criteria for the receive side selectivity of new devices. Doesn't NAVSOP go in the exact opposite direction? It appears NAVSOP devices would work best with no receive side selectivity at all. Assuming NAVSOP proliferates, we would end up with a GPS vs. LightSquared situation on steroids, not only affecting L1, but essentially affecting the entire spectrum. Now if an effort like moving television off of 700Mhz and into digital broadcast, users of NAVSOP would feel the pressure and start pushing up against such re-banding efforts. Am I missing something? How would such a situation be avoided?
surely nobody would be so cruel as to lie to a robot!
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
If GPS is denied to US consumers and military (for whatever geopolitical reason), would NAVSOP itself be vulnerable to jamming? From your base description, could NAVSOP be defeated if a E&M source transmitted that wasn't in the "master database" of frequencies?
When you are talking about pseudoranges measured in nanoseconds ...
Mmmmm super fast suede oranges.
That is done today. It is is called "Differential GPS" (DGPS) and "Real-Time Kinematics" (RTK). However, it's much more than just averaging - there are more complex mathematics involved to remove the errors common to both sets of measurements. RTK is done all the time in surveying and can achieve centimeter level accuracy in real-time. http://www.geod.nrcan.gc.ca/edu/rtk_e.php
So how does it feel to have played a pivotal role in finding particles that travel faster than light?
"I like to lick butts!" by MobileTatsu-NJG (#32700246) (Score:5, Informative)
How will the system function during/after a major solar event? Assuming a worst case scenario, satellites in orbit could be disabled for good. And depending on the severity, transmitters on earth may be affected as well.
Your thoughts?
in the land, air, sea and space domains
That pretty much covers everything, no?
It seems a lot of effort is going into bettering GPS accuracy by finding more triangulations (n-gations? :o) ) / reference signals. I was looking online at the WGD 84 earth model that the GPS system uses (http://en.wikipedia.org/wiki/World_Geodetic_System [wikipedia.com]) and read its accuracy was around +/- 1m. Since I often hear that GPS is accurate to about one meter (at least for the DoD), I wonder if this is why. That is, if we could get a more precise model (1cm? 1mm? LESS?), could we get that accuracy on our receivers, or is the error inherent in the GPS constellation/system itself? Thanks for your time.
What the OP asked is not "Differential GPS"; actually it is the opposite.
We can assume that if you measure GPS coordinates at a given time and location, you will have a systematic error (inaccuracy in satellite position, different speed of radio signal due to weather) that is the same for all GPS receivers in an area, plus a random error different from GPS to GPS. Taking lots of measurements would tend to cancel out the random errors and leave you with the systematic error.
With differential GPS, you put one GPS at a known location, compare its known location with its measured location, and you get the systematic error + random error of that GPS. Then you take a second GPS at an unknown location, subtract the known error of the first GPS, and your second location is known with (twice random error).
One key limitation with current GPS technology is the power requirements. Batteries in many handheld GPS units are drained in less than a day; 6-8 hours is an somewhat optimistic reality. What to expect from NAVSOP when it is available in a handheld form factor?
I'd like to fly drones over a, say, 100x100 meter area with centimeter precision, possibly indoors, for filmmaking. GPS is clearly not going to work, even outdoors. Time Domain sells a system with 5 cm resolution, using UWB technology -- but is there anything better than that?
I love Mondays. On a Monday, anything is possible.
RTK is often done based on a relative location from the base station. If a known monument is available, then the surveyor will usually set-up the base station over it, but if not, they often just use a landmark and do relative baselines.
Do you use Bayesian inference to combine positional information from many sources, some of which might be sorrily mistaken? I'd be interested in hearing more about the algorithms used to stitch this data together, and if there are any heuristics or approximations that help.
Expected time to finish is 1 hour and 60 minutes.
You mentioned earlier the domination of signal strength when indoors. Can you also use patterns in observed environmental data for automated mapping and exploration?
For example a robot exploring a cave or a large indoor structure like a power plant might be able to even use information such as ambient temperature / humidity, echoic nature of surroundings, or patterns in ambient air pressure / acoustic input from machinery or the sound of treads against floor.
Also someone was skeptical about using stars to navigate in the day. However radio telescopes can make observations in the daytime, which seems to be the ultimate sensor for your platform. Would your system work to find landmarks underwater too?
We bought our first GPS receiver in 1992 for $1500. Today we have GPS receivers for pennies in your cell phone with better accuracy. Why have costs not come down on higher end systems? Patents? Lack of Competition? For instance, in agriculture you buy a 1500$ receiver and the vendor sells you different levels of $2000 software unlock codes to go from 8" to 4" to 2" to 1.5" to 1" accuracy. Are they selling the receivers initially at a loss?
YEs, Differential GPS requires the position of the fixed receiver be known exactly. Then you can correct for the errors in the GPS position (which are due to ionospheric disturbances...) Those corrections can be applied to a roving receiver and it's accuracy can improved to the centimeter level. Surveyors, road construction crews, etc. use this method. If you've ever seen them at work, one person will hold a long pole about 8ft long with a round GPS antenna on top. There are markers in the road surface sometimes which they can use as reference points.