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Are the clocks in cell phones that precise? John Fenderson profile , 9 Sep 1: That's actually pretty slow by today's clock rates. Bengie , 9 Sep 9: GPS needs 4 signals because it measures 3 dimensions, cellphones only need 2 dimensions, so only 3 signals are needed. More are better if they can be used.
Ninja profile , 9 Sep 9: I've been seeing some professional applications of gps where they can get precisions of 1 centimeter after processing the raw satellite data. I'm inclined to think that acquiring more satellites will only get you up to a certain precision. Better sensors along with other geo location tools ie: As for the phone I think meters seem reasonable considering it usually can't pinpoint which lane you are when you have two parallel roads. John Fenderson profile , 9 Sep The way GPS works is that all the GPS satellites send out a synchronized timecode generated by an on-board atomic clock that has a precision of around nanoseconds, if I remember correctly.
Since all the satellites are sending the same timecode at the same moment, the receiver simply identifies when it has received the timecodes from all the satellites it can see, then compares the actual time they were received with the time they were sent the timecode itself. The discrepancies between the timecode and when the signal was received are then compared and used to "triangulate" it's not really triangulation, but similar to that.
US GPS satellites used to intentionally introduce a random fluctuation to artificially limit the accuracy, but they stopped doing that a number of years ago. So, the quality of the receiver affects accuracy in a number of ways, from how many satellite signals it can receive, to how quickly and accurately it can do the math, to how accurate its timekeeping is. Inexpensive GPS receivers such as in phones are not terribly accurate.
The actual limit, if you're only using GPS signals, is 10cm. However, you can increase this resolution by using things like fixed ground-based GPS refrerences. David , 9 Sep Even with 4 satellites, it can be worse than that. Reflections off nearby glass buildings can put your location off by a couple of blocks sometimes, too. In some parts of downtown which has plenty of glass and metal high-rises , the GPS will almost always put me a few blocks away from where I actually am.
GPS is good to about 30 feet 10 meters , but the cops don't know that either. A few years ago, a friend was run over and killed while riding his bike home from his night-shift job. Part of the "evidence" used to claim that he somehow deserved to die, was that the GPS data from the app he was using to record his bicycling activity put him in the street instead of on the sidewalk, 3 feet away and BTW, map-aware programs will often 'snap' your reported GPS location to roads. Celebrim , 10 Sep That said, an error of up to 1m is hardly unbelievable, and in the case your example you'd also have to accurately measure the position of the roads rather than rely on maps since the data on the map could be wrong, or as you said, the application could be influencing the data.
I'd consider GPS data to be useful to only to strengthen other physical evidence position of the bike, marks on the road, example. GPS data in the absence of other physical data or contradicting other physical data is useless. I don't believe "GPS is good to about 30 feet". I've owned several GPS phones over the years, and their accuracy varies widely. I'd love to know why. I'd love to see a review comparing the accuracy of GPS in different phone models. Nina , 2 Jul 4: Agree, even those apps which claim that they are specifically designed for accurate mobile monitoring can't not suffer from GPS errors.
Resulting glitches and customer disappointment. Even paid parental control apps like thespybubble. Georgia Watson , 8 Oct 2: In non-tech words, what does this mean? I have worked with E services. Inwoods profile , 9 Sep 8: I assumed e WAS what they used to locate. Does that have to be set off remotely first? Could you expand on that a bit?
My understanding is that when there's multiple towers, the signals can be triangulated and the location of the phone can be calculated accurately. That's how, for example, the map application in a phone knows where the phone is located. As far as I know cell phones do not use the GPS sat signals.
They triangulate their location based on cell towers using the method I described. Which is why I keep an ancient Tom Tom around. When I don't have a cell signal the Tom Tom still functions. Trigger profile , 9 Sep 9: This is not correct. I can access GPS information when I don't have cell signal. What you might be thinking of is you can't access the maps without cell signal, but if the maps are already downloaded then it works fine. Google recently released an update to Google Maps to do exactly this.
The chip to get GPS signal is really tiny, from there it's just processing. I had a USB one for my computer that was smaller than my watch and it was mostly plastic for extra protection.
My laptop at the time was less powerful than my watch. JF profile , 9 Sep 9: I always assumed that when I lost cell signal and the map app refused to work it was due to the fact it couldn't triangulate my location due to lack of signal. Why don't map apps make it easier to choose to download the maps if they work when you don't have signal? Trigger profile , 9 Sep Depending on the source, map data can be anywhere between 2G and 6G.
That's a hell of a lot of data to transfer with a caped data plan. Then you've got to keep it up to date. Easier just to keep all that on a central server since most of the country is covered in cell towers or at least WiFi. There are apps for Android that do download entire map packages, but last I saw they were the on the old business model. You had to pay for the map and then pay for each update.
With its free version OsmAnd you can download up to 10 maps for free. Google maps is one of the exceptions to this -- but there are numerous alternatives. Jeremy Lyman profile , 9 Sep You can save a map extent for offline use in the current version of Google Maps for Android at least by zooming to the extent you want, touching the search box, and scrolling to the bottom of the suggested locations list. There will be an option to "Save map to use offline" at the bottom. Yes, unless you haven't updated Maps there were a few releases where saving offline maps wasn't supported at all.
But I wouldn't call this "pretty easy", I'd call it "cumbersome and obscure". Usually the phones fine tune the location using tower signals as well and sometimes even wifi by comparing ssids in the area with online databases yay Google street.
That feature that allow you to save the map data from certain places is useful indeed. I was using Osmand for offline navigation outside mobile coverage or where you only get crappy 2G. I dont know if this article is acurate I have always assumed when they talked about locating a cell phone it was triangulated. Im sure there are time out in the country where the phone cant sync the timeing signals from the three closest towers but for most metropolitan areas I would say trigulation by cell phone is very accurate.
John Fenderson profile , 10 Sep 8: Even the law doesn't require anything like great accuracy. Pete Wilson , 29 May 3: A few years late, but that is completely wrong. AGPS is full blown satellite GPS, but with location and especially startup assisted by cell tower location information, as full blown GPS startup can take over 30 seconds when the GPS has no idea where on earth you may be. John Fenderson profile , 9 Sep 9: Tower triangulation is never precise, but the more towers that can see the phone, the more accurate it is.
By the way, those requirements are: People however do confuse GPS and Tower triangulation - they are two separate things, both of which can locate where a device is being used. As far as the triangulation goes, if someone is in a location where they can reach multiple towers both of their own carrier or others you can get it down to about a 6ft diameter area of where a person is using the tower data alone. Identifying your location with GPS or Cell tech uses the same principle.
How long does it take a signal to reach you? Since we know how fast the signal travels we can calculate how far you are from the signal origin giving us a radius. A single signal source means you can be anywhere on the circumference. With a second signal source you now will have 2 points where the signals overlap that you can be at. A third signal point reduces it to a single point. The exact location of that single point is further refined by your timing of how long it took the signal to reach you. Of course, this calculation is for 2D.
If you want elevation you will require a fourth signal point and instead of imagining 2D circles you will use a 3D sphere. Charles Bernardo , 9 Sep 8: Possibly it would of been good to talk to a RF engineer or a carrier spokesperson on your information before printing it. These are evaluated daily by carriers to determine coverage and capacity issues.
Federal Legislation under enhanced E requires an accuracy within ft of the handset. Anonymous Coward , 9 Sep 9: There is a difference between a live query, where is this phone now, and the querying the much more limited data that the phone company stores. I would expect, and the statement suggests, that only very limited 'event data' is actually stored, like time and tower when a phone connects to and disconnects from a tower. This makes perfect sense because of the orders of magnitude, 3 or 4, between 'event data' and second by second data from several towers.
This may if useful to the company, include location data for the event, when they wish to survey coverage, or locate the boundaries of a black spot in there coverage. Otherwise they would be storing data that they do not need, and that eats into their profits. This would not preclude them using live location data, if they could use it to sell customers to advertisers, but they would have no reason to store the data. Yes, not live tracking. All the talk about GPS location has confused the issue a bit. The devices can triangulate their live position from multiple towers or satellites for GPS and the device may relay that to a operator or Google, etc.
However the information available to law enforcement weeks or months later is only what business records the phone company has chosen to keep. This varies from company to company along with the retention period of records but normally it is a single tower location, a time and an antenna ID. Most towers are composed of three antennas offset to provide degrees of coverage, so each antenna ID corresponds to about degrees of sweep.
Analysts can evaluate tower location for elevation, obstructions, and competing towers to provide rough estimates for the maximum distance from which a device is likely to connect. It is generally several miles. This provides a large swath of coverage that the phone is deduced to have been inside of at that time. If the device quickly "bounces" back and forth between that and another tower or two the coverages may be overlaid to perform a crude "triangulation" but nothing close to GPS.
The odds that a device would bounce during any specific event, and that all the records would be kept, are pretty low. This information comes from my having served on a federal jury and being presented with phone record location information and analysis. I was very surprised at the time because I assumed it would be much, much better.
Thrudd , 9 Sep 8: Mathematics or in this case trigonometry at even a grade school level is not required to be a lawyer or work in law enforcement. As has been already documented, math science and logic are discouraged from an early age. As for the signal travel time - I highly doubt the dollar store towers would have that capability. You are stuck with needing a minimum of two to triangulate as long as you can get a direction. That is kyboshed to a 10 meter error by the USA.
You can get better with the right surveying software and time OR receive the Russian signals OR wait for the EU to finish their system. There is also ground based nodes in some cities that compensate for blocking LOS to the satellites. Even that error can be reduced or eliminated by using fixed groundpoints. This speaks as much to the unfairness of the plea bargain system as it does to cell phone location technology. Someone being sufficiently frightened with false information so as to take 15 years for a crime they didn't commit invalidates the whole process.
Don't think law enforcement and prosecutors didn't know they were spieling nonsense. They knew exactly how inaccurate the information was; they just didn't care, as long as it yielded a confession. The existence of plea bargains is in my top 5 things that are the most harmful to actual justice, and leads to the conviction of innocent people. But if you're told that you'll be indicted for murder with possibility of the death penalty, you might be more inclined to do 15 years rather than risk losing your life.
Agreed, pleaing some guilt rather than risk a false conviction by over-zealous prosecutors is not what our justice system is supposed to do. Unfortunately, I feel that I have too much cynicism in the authorities to ever be allowed on a jury. First, 15 years is a substantial amount of time. Aside from that, though, a murder conviction effectively destroys your life whether you spend the next 15 years or the next years in prison.
You're pretty much done for either way. Anonymous Coward , 9 Sep 1: Really getting confessions or plea bargins on false information should be a "twenty five years to life" felony offense. That shit is not acceptable at all. Not to mention it undermines the plea bargain system. If they can't be trusted on the evidence presented that gives reason for the accused to flood the courtrooms in case the DA really has nothing on them. My Samsung Galaxy S3 running Android claims to use be able to use GPS, wi-fi, and mobile networks towers in order to determine its location.
However, the phone I had in had no GPS capability whatsoever. As I understand it, it can do this because it can see multiple towers and triangulate. The question--which still seems unanswered in the article and comment thread--is whether this works the other way. Can more than one cell tower "see" a phone and its signal strength at a given time? Or does the phone simply look for cell signals passively to decide which tower to connect to, meaning that only the connected tower sees the phone?
If more than one cell tower can "see" a phone at a given time, the phone company would then be able to nail my phone's location to the same precision as I see on my phone, right? In fact, they have to in order to make decisions about when and where to do handoffs to neighboring towers when the phone is in motion. Cell Tech , 10 Sep 8: John Fenderson's comment to pick just one is a perfect example. What one tower can see, the others cannot. A system operator would have to target a specific phone and force it to talk to several sites in turn. Each site can time a round trip, which the backend can then use to triangulate.
As far as knowing where everyone and their phone has been, cellular systems just store what sites every phone registers to and when. Once a phone has registered, the system does not know, or care, where in the service area the phone is. Phones only register on service area changes because that is what the system uses to know which sites the sites comprising your current service area have to page your phone when you get an incoming call or message. So no, they're not logging everyone's location with any geographical precision or on a frequent schedule.
Carl "Bear" Bussjaeger profile , 9 Sep What's actually happening in cell phone location is this: There are three separate processes used to locate a cell phone: In case it got misplaced — users use the iCloud service to locate the device on the map.
In such circumstance, there is an option to play a sound on the target device so that it immediately reveals its location. This requires an active internet connection in order to work as is intended. This can be a phone number or address that will be useful for those that happen to find the lost device. Apple Pay feature also gets immediately suspended as well as any other credit or debit cards info stored.
Tracking of the lost iPhones and other iOS devices is very accurate. Using the iCloud online service users can monitor the location of their device in real-time on the map. Devices displayed with green dots represent online and devices with grey colour represent offline status. Apple points out that the location is an approximation of the devices current or last location however in our use we found that it is very accurate in tracking and displaying the position and location at any given time.
Using the map users can Zoom into the street level detail and greatly enhance the location information at any given time. We have to point out that the tracking accuracy and location services greatly depend on the state of connectivity of the device and sometimes if the device is in a low signal are it cannot lock onto the satellites or connect to cell towers thus not be able to send its location data.
Users can increase the chances of finding their misplaced devices by following some simple tips that will help keep their iDevices safe at all times. When at work or outdoors make sure not to live your device disconnected from a data connection or Wi-Fi networks you use. At home make sure to leave your devices on desks, nightstands or any place where you glance often and keep other items of importance. Leaving your device in bed can lead not only to loss but also permanent damage. Devices left underneath pillows and in sofas often cannot be heard so dialling and trying to locate them by sound will be useless.
Tracking will not be of much help as it will show your house location and precise room based position. In the case of theft notify authorities and supply them with the current or last know position of your stolen device by using an iCloud map and Find my iPhone functionality.
In order to be able to do so, it is necessary that each family member sets up and allows sharing their locations with the rest of the family. This provides the distance that the satellite is from the receiver. This allows the phone to lock in on a position much more quickly than it could otherwise. The most common use of this functionality is to track the location of children who are on a family plan. All the talk about GPS location has confused the issue a bit. Let me know if this is something that might be of interest to you. The advantage of network-based techniques, from a service provider's point of view, is that they can be implemented non-intrusively without affecting handsets.
In many cases, iPhones with that have always enabled data connection can be found and recovered very fast so make sure to react as quick as possible. Jason Mallins February 7, How to keep track of your iPhone — the easy way? How do I use it to find my lost iPhone? How accurate is the iPhone tracker?