Well, I am not an expert here, but i had to do some professional research at some point on this topic. Current phones relies on many many things to try to pinpoint your location, even without satelite navigation. It of course triangulates you via known cell emitters, and wi-fi hotspots and combines accelerating detectors in your phone with some specialized SW code. Heck, some SW might even use camera (light detection, photo timers, etc) or even mic to help to determine where you are. Results can vary of course, but you might be pinpointed to inches even when and where you thought that it was impossible.
About 15 feet but it is improving.
The situation is changing because of several reasons. Several other countries have launched satellite constellations that do much the same as the US GPS system. The European, Japanese and Chinese systems have been very busy launching satellites into constellations and they are operational and will be complete in two year. The US and Russian systems are also being upgraded for better accuracy. Secondly the chip makers have been bringing to market GPS chips that can listen to the signals from several of these satellite constellations at the same time. Previously only professional equipment could do this but now there are chipsets aimed at the mobile phone market.
The European Galileo system helpfully provides a list of phones:
https://www.usegalileo.eu/EN/inner.html#data=smartphone
This site is good for a deep dive into the subject of how good the best smartphones can be compared with professional surveying equipment.
There are some extravagant claims about new chipsets with the accuracy will be down to a foot. But not for a few years, I think.
There are some smartphone apps that can tell you how accurate your phone is. My old iphone 5 is good for only 33 feet at best and it has trouble seeing more than the minimum 4 satellites so it falls back to trying to work out my position by measuring the strength of the cell phone signal from transmitters in adjacent cells which is far less accurate, hundreds of feet either way. Lots of devices nearby and, I think a lot of radio interference for GPS.
Seems there is a lot of smoke and mirrors at the moment regarding claims of high accuracy GPS on smartphones.
This guy seems to have the straightdope.
Isn’t there a security issue with extremely accurate GPS?
The military can thread a missile right through Putin’s bedroom window. That tech was used in the Iraq war over 15 years ago.
I don’t imagine any government wants that capability in civilian hands.
Image getting accurate gps coordinates for a state legislature’s chamber. That would decapitate a state’s government in one stroke.
It’s a possibility to defend against. Not anything I’m in any way suggesting.
To be clear, are we talking about GPS specifically, or about all of the techniques phones use to determine their location, combined? And if the latter, are we in an urban or rural environment?
Civilians would have difficulty (though it’s not impossible) building all the other stuff involved in such a terrorist attack as described. Earlier, when it was discussed how dangerous drones carrying bombs were, I computed the cost per payload - basically, yes, someone could have 2 large drones each carrying about a 1 lb bomb. Or, for the same cost, someone could fill a cement truck to the brim with explosives and deliver many tons of explosives to the target.
Basically, it’s not the accuracy that becomes a problem - someone could just remotely control the drone or bomber or whatever. It’s actually that the cost of flying things, whether they are missiles or use propellers or jet engines - are incredibly expensive.
There must be an app somewhere that allows you to do something analogous to time integration/lucky imaging/synthetic aperture: Take many samples and see where they intersect to get increasingly precise measurements.
To increase accuracy would it be helpful to have more data, like multiple devices from multiple carriers and use all of the features available for location.
Or what if you built something that held a little cluster of phones X feet away at 3 or 4 different points, from your location, in conjunction with the one in your hand.
Could the extra data be used to improve the accuracy? Or is it randomized and evenly distributed across the area making it tough to improve?
There were originally claims about security and there was a feature called Selective Availability (SA) was an intentional degradation of public GPS signals but that was shut off a long time ago.
The US GPS shut that off a long time ago, and it would add 100m of error to the signal.
Now every phone uses multiple countries GNSS (acronym for the collective set of all countries services) so while the US GNSS service GPS can still shut off the public signal it would require Russia and the US and other countries to simultaneously shut off their services to loose all service. As critical safety services like airplane approaches use GPS now it is doubtful if the US would shut off the public signal. There is still the encrypted signal but that is more about authenticating the signal for military use these days.
The chip-sets can use the various services to improve typical accuracy, but to get to the centimeter level of accuracy you have to have a ground based signal from a known reference point for correction and/or an antenna large enough for multiple receivers and the ability to detect phase as well as the antenna being configured and oriented to ignore ground reflections.
The latest development in the micochips that provide global positioning is the ability to deal with two different GPS frequency bands at the same time. Most mobile phone chips can tune into multiple constellations in the L1 band. A new generation of chips can tune into the L1 and L5 band simultaneously. This improves the accuracy and also the reliability.
The Broadcom BMC47755 seems to be the one that is being sold to high end mobile phone makers. But mobile phones actually on the market are few and far between at the moment and there don’t seem to be any tests that confirm their performance so far. These are mass market chipsets rather then the specialist low volume chips sold to the makers of surveying equipment. Survey equipment uses a lot of techniques to get accuracy down to centimetres but it is expensive professional equipment.
The other factor is the part of the world you live in and what GNSS constellations provide a service. Several of the constellations have not completed their launch schedules and the global coverage is improving each time a new satellite goes up and is commissioned.
The progress in this area is of keen interest to the drone and self driving auto industries and all the other new businesses that rely on accurate location based services. The tricks mobile phones use in urban and domestic environments don’t really work outdoors in large mobile phone cells, away from those helpful wifi, bluetooth signals that can provide helpful clues. Out there, you have to rely on the GNSS signals, but at least there is clear view of the sky and you are well away from electrical interference.
Maybe your next mobile phone upgrade will have one of these news chipsets. Until then the accuracy is not so so impressive. It kind of explains why the app that shows the progress of an Uber cab is sometimes quite confused.:dubious:
Since I got some people wondering about my intended use; basically was wondering if were possible to develop an app with a database that could help people locate specific items or departments in stores. Need to find where microwave ovens are? Check the app; things like that. But the stores would have to buy expensive tech, I think, to make that happen. Probably more practical and way cheaper to just print a floor plan.
Bluetooth localization. Store would have a ceiling mounted grid of cheap Bluetooth transponders. App would measure the relative signal strengths for a simple and accurate position fix.
Or ask a store employee.
Heck, you could probably do it already without needing any additional infrastructure on the store’s part, just by looking at the signal strengths of their WiFi transmitters.
FYI, this sort of thing (using smartphones to find one’s way around a building) is often called “wayfinding” and there are various hardware/software solutions for this sort of thing. It’s particularly of interest to hospitals or airports.
Sorry if this is an impossibly stupid question, but is my iPhone (5SE, small body but the tech of a 6) actually using a signal from a satellite when I open up Waze? I assumed it was all Wifi/cell tower signal.
It uses all three, Cell Tower triangulation, wifi naming maps and GPS.
In an urban area the error in your location is about:
Cell towers: ~1000+ feet
WiFI: ~100+ feet
GPS: ~10+ feet
So obviously waze will typically use the GPS signals when at all possible
Plus inertial navigation to bridge gaps in coverage.
And GLONASS for those times when GPS coverage is unfavorable.