Very useful. Not.
I can't even think of a place on the Earth that would not have satellite GPS coverage but have readily available LTE and WiFi.
With both the US and Russia researching Global Positioning System (GPS) jamming, it's heartening to see boffins working on navigation systems that don't rely solely on satellite signals. Research led by the University of California Riverside (UCR), and presented at a navigation system conference in mid-September, demonstrated …
And the wifi and LTE signals are immune to reflection?
Getting into the details, GPS signals are right hand circular polarization (RHCP). CP signals become opposite sense (e.g. LHCP) upon reflection at non-grazing angles. Provided that your receiver is using a RHCP antenna (small and cheap gear probably isn't), it would have improved immunity to reflected GPS signals.
The system designers did their best.
Not necessarily true, about 5-6 years ago I was in a light aircraft and the instructor demonstrated the frowned-upon practice of putting an AM radio frequency into the ADF (https://en.wikipedia.org/wiki/Radio_direction_finder#Automatic_direction_finder_.28ADF.29) - the needle duly swung to point in the direction of the transmitter. The one he used was 1215 kHz (247m), but he said it also worked on 252 kHz (1190m).
Take readings from two stations/beacons and you have a position fix; the only problem is the equipment size (and keeping it upright).
@ S4qFBxkFFg Yes you can use the ADF with AM transmitters, but even using proper ADF or VOR beacons, how good is your fix? 1 mile accuracy is plenty good enough for an enroute report, or establish your location visually, but is never going to get you a fix to within the width of a road lane, which is what an autonomous vehicle needs.
S4qFBxkFFg offered "...light aircraft....Take readings from two stations/beacons and you have a position fix..."
Do the math (+/- 1° times two), plus take into account your ground speed and the time if requires to take these measurements, you'd be very lucky if it's within a square km.
Navigation yes. Provided you have a steerable antenna.
GPS replacement, no.
And don't get me started on AM broadcast band skywave at night. That'll mess up your signals.
@ druck, JeffyPoooh
Absolutely - what you're saying is right - to clarify, I certainly wasn't trying to suggest MW/LW signals can be used as a GPS replacement suitable for road vehicle navigation, just that they could provide useful information, especially if combined with input from other sources.
"Coming up next: how to use a map and a compass."
IIRC an examination board in England is dropping various subjects - one of which includes navigation by the stars and calculating distances on the surface of a globe. Sorry - can't find the online article.
Are GCSE pupils still taught how to read an Ordnance survey map and the geographic features influencing the position of towns?
"Coming up next: how to use a map and a compass."
Yeah, that would be really useful to a drone doing ~10MPH down a crowded LA street or to a Google car doing ~70MPH on a motorway...
I know it's big and clever nowadays to mock people who use GPS and "don't know how to use a map" but not every use of GPS is by people.
And, if individuals can benefit from the technology then why not? For leisure travel in cars and on motor bikes GPS can mean the discovery of new routes and the ability to explore without fear of becoming lost and having to stop and take bearings with a compass.
So, while I am in agreement that the use of a map and compass is a skill worth having and that having at least a paper map when driving is a very good idea I don't think either are relevant here.
In other news, why bother with keyboards when one can simply learn how to write?
Pretty sure I recently read about an advance in acceleration MEMS that would make dead reckoning work well enough that you could go for hours without a GPS fix and still have well under a meter of position error.
That would be the ideal, as you wouldn't need a constant fix just an occasional really good fix to correct the accumulated error. The rest of the time you wouldn't need to rely on any outside signal sources. Probably the best way to get such a super accurate fix for a car would be (longer range) NFC type devices built into the road every few miles that the car can read to fix the tiny accumulated dead reckoning error.
Building devices into the road would also fix the "Australia problem", since as the continent moves, so do the roads and everything built into them :)
"Building devices into the road would also fix the "Australia problem", since as the continent moves, so do the roads and everything built into them :)"
But what about the "New Zealand Problem" where their islands move inconsistently (as in not at the same rates at all points, meaning some masses extend while others contract)?
"The researchers note that current GPS navigation, even supplemented by inertial navigation systems (like gyroscopes), isn't accurate or reliable enough for fully-autonomous vehicles."
Isn't Iridium meant to be accurate to at least a metre (1/15th a london bus in old parlance)?
"Are GCSE pupils still taught how to read an Ordnance survey map and the geographic features influencing the position of towns?"
They weren't taught it back in the '90s (only in optional things like DofE, not compulsory classes), so I very much doubt they are today. For those of us who actually like the outdoors, it's easy to forget just how rare it is for anyone to actually need to read a map with that amount of detail on it. Even if you get completely stuck with no GPS or internet, a decade old AA road atlas is more than good enough for most people the vast majority of the time. And if even that fails, you can always resort to the horror of actually asking someone for directions. For people who generally stick to roads or relatively urban areas, reading proper maps just isn't a useful skill.
@ Oh Matron!
Iridium may be accurate to within a metre, but an autonomous car that drives a metre off the road wouldn't be very useful. Probably good enough for major roads that have space at the sides, but on a narrow country lane or the middle of a town, that's easily inaccurate enough to land you in a hedge or a pavement full of pedestrians.
> They weren't taught it back in the '90s
I was (Southern Examining Group, early 90s), and we got a Landranger (IIRC) extract along with the exam paper on which we had to take measurements and answer questions.
Apparently a good ruse was to claim you were colour-blind: the invigilators were then permitted to assist you identify features on the map, which as good as answered the exam questions for you…
I mean of course you can for example use DVB-T signals of a SFN and estimate the distance differences to the individual transmitters. However that requires a receiver that can tune to those frequencies as well as process them in a way to estimate the impulse response.
It's much simpler to just ennumerate the WLAN access points and then go from there. WLAN chipsets are cheap as they only need to work on a comparatively small band.
So in short its one of those things that are fun to try, but probably won't have much practical use in the foreseable future. Just like those "Lifi" setups which transmit data via LED lighting.
Tuning to particular frequencies shouldn't be a problem, a cell phone is able to tune to multiple different ranges of frequencies for all the various wireless standards. You can get satellite IF band tuners that digitize a 2 GHz+ range and support multiple demodulators working in parallel anywhere in the band. So I really don't see that part as a problem.
Assuming the cell/TV towers are broadcasting a highly accurate time source (altering regulations to make them do so if they currently aren't, I suppose) and the receiver has a highly accurate clock - i.e. one of those newfangled atomic clock on a chip (assuming mass production of millions of them would bring the price down to reasonable levels) then determining distance from the source is simple enough. Obviously along with the highly accurate clock you'd want them to broadcast their exact GPS coordinates - that will aid you in determining if you are seeing reflections or the original signal. That's not foolproof, but using voting type methods you can throw out signals that don't make sense when they disagree with the others you are receiving.
Then your only problem is pinpointing the exact direction where each signal came from. This is what I think the problem would be. Using MIMO you can get a pretty good fix, but well enough to triangulate your position to the same level of accuracy as GPS? I highly doubt it. Maybe on a car if you had antennas on each corner of the roof you can get enough resolution, I don't know.
With then demo I saw a few years ago they didn't need to know the position of the transmitter but it helped. If they didn't know the location they just needed a few accurate references (e.g. starting GPS coordinates) and they could then use those to locate the alternative transmitters, when the GPS signal was lost they had enough information about the 'signals of opportunity' to carry on with some accuracy.
WiFi might give you a location but it is never accurate. SOO can be used for accurate positioning in areas that GPS can't. I've seen a demo a few years ago by a UK military research company where the researcher was able to show continuous location tracking inside and outside a building. It spotted a single GPS satellite as he passed a window and otherwise used local terrestrial masts for its references.
I was amazed at the time, glad to see someone a few years later doing it again (*cough* its not new *cough*) but I'd really like to see someone commercialise the concept.