Turns Out Cell Phone Location Data Is Not Even Close To Accurate, But Everyone Falls For It

from the because-of-course dept

We've frequently talked about law enforcement and the intelligence community accessing and making use of cell site location data, which looks to figure out where people are based on what cell towers they're connected to. Law enforcement likes to claim that it doesn't need a warrant for such data, while the NSA has tested a pilot program recording all such data, and says it has the legal authority to collect it, even if it's not currently doing so.

However, as anyone with even a basic geometry education recognizes, which cell tower you're connected to does not give you a particularly exact location. It can be useful in putting someone in a specific (wide) area -- or, much more useful in detailing where someone is traveling over long distances as they repeatedly switch towers in a particular direction. But a single reading does not give you particularly exact location details. I had naturally assumed that most people understood this -- including law enforcement, lawyers, prosecutors and judges -- but it turns out they do not. A rather depressing story in The Economist notes that, thanks to this kind of ignorance (combined with bogus cop shows on TV that pretend cell site data is good for pinpointing locations), cell site location data is frequently used to convict innocent people. The story opens with a ridiculous example, in which a woman was pressured into a plea bargain based on totally false claims about tower location data:
SOMEONE strangled a prostitute in Portland, Oregon in 2002. The police arrested Lisa Roberts, the victim’s ex-lover, who spent more than two years in custody awaiting trial. Shortly before the trial the prosecutor told Ms Roberts, via her lawyer, that tower data collected by Verizon, her mobile-telephone network, showed precisely where she was at the time of the murder. As her lawyer recalled, the prosecutor said Ms Roberts could be “pinpointed” in a park shortly before the victim’s naked and sexually assaulted corpse was found there. She was told she faced 25 years to life in prison. She accepted a deal to plead guilty and serve 15 years.

But the high-tech evidence against her was bunk. Routinely collected tower data can place a mobile phone in a broad area, but it cannot “pinpoint” it. That would require a special three-tower “triangulation”, which cannot reveal past locations. It took a decade for Ms Roberts’s guilty plea to be thrown out. On May 28th she left prison, her criminal record clean, after nearly 12 years in custody.
Obviously, things like GPS do allow for much more precise targeting of location (which may be why the NSA is focusing on that instead of cell site location data), but too many people confuse cell site location data with GPS. What's ridiculous is that this mistake isn't just being made by random people -- but prosecutors and lawyers responsible for criminal cases that can destroy an innocent person's life.

This really points to a larger issue: people have this tendency to believe that technology can answer all questions. The NSA's fetishism of surveillance via technology is an example of this. There's data there, so it becomes all too tempting to assume that the data must answer any possible question (thus, the desire to collect so much of it). But the data and the interpretations it can lead to are often misleading or simply wrong. And that's especially true when dealing with newer technologies or forms of data collection. That the criminal justice system could go decades without everyone recognizing the basic geometric limits of cell site location data based on a single cell is... both astounding and depressing. But it's also a reminder that we shouldn't assume that just because some evidence comes from some new-fangled data source it's automatically legitimate and accurate.

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  • icon
    Ninja (profile), 9 Sep 2014 @ 7:17am

    I recently checked my location data on Google (I have history enabled on this because it's useful for me and I reset it every once in a while) and I was amused to see that when my gps is off my phone gets plotted over 3 km away from my usual route (into places I've not been to). I attribute part of it to the tower issue and part of it to the fact that it falls back to some Internet node that is located at that specific place. So, yeah, location data is some sort of rough approximation unless of course you got a GPS. And even then there are quite a few meters of difference. (On a side question, what's the precision of phone GPS?)

    Anyway back to the story, it's good to rise awareness of these issues because people will be better equipped to counter such "evidence". Also, this pleading guilty thing seriously needs to change in the US.

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    • icon
      Josh in CharlotteNC (profile), 9 Sep 2014 @ 8:13am

      Re:

      (On a side question, what's the precision of phone GPS?)

      The short answer is how many GPS signals you're getting.

      "In typical GPS operation, four or more satellites must be visible to obtain an accurate result."
      http://en.wikipedia.org/wiki/Global_Positioning_System

      GPS can be just as bad at pinpointing an exact location as cell site location if you don't have 4 or 5 satellites in view. With 4 clear signals, accuracy is 6-12 meters. Can't find specifics on less, but I know I've been in situations where my phone thinks I'm half a mile or more away from where I actually am (frequently indoors in a very large building, so probably getting less than the 4 signals).

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      • identicon
        Anonymous Coward, 9 Sep 2014 @ 8:35am

        Re: Re: GPS Accuracy

        You absolutely need 4 or more GPS signals to get a fix. Reason is that there are 4 variables to solve. Location in 3 coordinates plus time. Now for specialized situations (time keeping with a fixed location), you can get by with only 1 GPS signal. Reason for that is because the geographic location of the receiver is fixed and already known. But for a mobile receiver, you need a minimum of 4 (unless said receiver happens to have an atomic clock. But phones definitely don't have such a stable time source).

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        • icon
          JF (profile), 9 Sep 2014 @ 8:49am

          Re: Re: Re: GPS Accuracy

          Even if your location is fixed how do you determine your location with only one GPS signal?

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          • identicon
            Anonymous Coward, 9 Sep 2014 @ 11:20am

            Re: Re: Re: Re: GPS Accuracy

            You don't, you already know where you are.

            If you're at a fixed known location you can calculate what signal you should be receiving from any one GPS signal. It in essence can confirm your location, but as you already knew where you were there isn't a lot of value in it. Unless you are checking to see if you've moved. In which case you'll confirm you know where you are, or you'll know you're lost.

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          • identicon
            Anonymous Coward, 9 Sep 2014 @ 11:26am

            Re: Re: Re: Re: GPS Accuracy

            If your location is fixed, a GPS time source will use 4 signals to determine the location and time. Once the location is then known, just 1 signal is needed to determine the time. Simple math. You need as many signals as there are unknowns to determine. Location is three unknowns. Time is another. If you know 3 of them (location), then you just need 1 signal.

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        • identicon
          Michael, 9 Sep 2014 @ 10:01am

          Re: Re: Re: GPS Accuracy

          It takes 3 GPS satellites to get pretty good accuracy, 4 to get very good accuracy, and more satellites will continue to improve the accuracy.

          GPS uses times being sent by satellites that are in known positions. The clock in your phone is nowhere near accurate enough to use, so the times sent from the satellites are actually used to determine what time it is at your location as well as the distance to the satellite. GPS receivers assume you are on the face of the planet, so if you knew the time, you would know the distance to two satellites and your location, but you need at least a third to determine the time and then would need a fourth to stop assuming the altitude. After that, additional satellites will help your device calculate a more accurate time at your location and that will make the distance to each satellite more accurate.


          As for the cellular end of this - the cell towers do not transmit hyper-accurate time information and their locations to your handset, so at best you can get intersection information based on signal strength - the time the signal takes to get to the cell phone cannot be measured by the equipment in the phone accurately enough to be worth anything.

          What IS happening now is the phones are using GPS technology for E911 and transmitting it back to the towers so the towers do actually have an accurate picture of where the phone is.

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          • identicon
            Anonymous Coward, 9 Sep 2014 @ 10:24am

            Re: Re: Re: Re: GPS Accuracy

            Several models of cell phones have a barometer. They can use the ambient air pressure to estimate the altitude, combined with an approximate position guess from cell towers and wifi access points, and a timing guess from the network (cell or NTP), and get a faster GPS fix (a GPS fix is faster if the GPS knows somewhat where it is).

            "As for the cellular end of this - the cell towers do not transmit hyper-accurate time information and their locations to your handset, so at best you can get intersection information based on signal strength - the time the signal takes to get to the cell phone cannot be measured by the equipment in the phone accurately enough to be worth anything."


            Have you ever heard of "timing advance"? Yes, it measures the time for the signal to get to the cell phone. It is used as a timing adjustment (thus the name) so that, when the signal arrives on the tower, it does not step on the signal sent by other phones nearer/farther the tower.

            It's easy to measure the distance with radio: send a "ping" to the other side, wait for the answer, and divide the time it took by two. That method is even used to locate deep space probes with high precision.

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            • icon
              nasch (profile), 9 Sep 2014 @ 12:27pm

              Re: Re: Re: Re: Re: GPS Accuracy

              It's easy to measure the distance with radio: send a "ping" to the other side, wait for the answer, and divide the time it took by two

              Assuming the signal travels at 300,000,000 meters per second (it doesn't since it's not in a vacuum but this is ballpark), to get 10 meter resolution you need a clock accurate to 1/30,000,000 of a second. Are the clocks in cell phones that precise?

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      • identicon
        Bengie, 9 Sep 2014 @ 9:27am

        Re: Re:

        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.

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      • icon
        Ninja (profile), 9 Sep 2014 @ 9:42am

        Re: Re:

        Interesting. 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: cell phone towers?) and post processing would be needed to get better precisions.

        As for the phone I think 6-12 meters seem reasonable considering it usually can't pinpoint which lane you are when you have two parallel roads.

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        • icon
          John Fenderson (profile), 9 Sep 2014 @ 10:03am

          Re: Re: Re:

          "I've been seeing some professional applications of gps where they can get precisions of 1 centimeter after processing the raw satellite data."

          Yes, this is possible.

          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 100 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.

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          • icon
            John Fenderson (profile), 9 Sep 2014 @ 10:20am

            Re: Re: Re: Re:

            "Yes, this is possible"

            Actually, I was wrong. 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.

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      • identicon
        David, 9 Sep 2014 @ 11:46am

        Re: Re:

        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.

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        • icon
          John Fenderson (profile), 9 Sep 2014 @ 11:52am

          Re: Re: Re:

          Indeed yes. 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.

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    • icon
      mudlock (profile), 9 Sep 2014 @ 2:23pm

      Re:

      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.)

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      • identicon
        Celebrim, 10 Sep 2014 @ 10:54am

        Re: Re:

        A decent GPS is consistently accurate to about 10cm these days (>90% of measurements). 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.

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      • icon
        bobd (profile), 17 Apr 2015 @ 10:01pm

        Re: Re:

        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.

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    • identicon
      Nina, 2 Jul 2016 @ 4:24am

      Re:

      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.com/ are not the exception, not to mention all free software presented in google play and itunes

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  • identicon
    Anonymous Coward, 9 Sep 2014 @ 8:14am

    A single tower? No. Multiple towers? Yes.

    Source: I have worked with E911 services.

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    • icon
      Inwoods (profile), 9 Sep 2014 @ 8:25am

      Re:

      Huh. I assumed e-911 WAS what they used to locate. Does that have to be set off remotely first?

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    • icon
      antidirt (profile), 9 Sep 2014 @ 8:28am

      Re:

      A single tower? No. Multiple towers? Yes.

      Source: I have worked with E911 services.


      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. Mike says "too many people confuse cell site location data with GPS," but I don't believe phones even have GPS. Is that right?

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      • icon
        JF (profile), 9 Sep 2014 @ 8:32am

        Re: Re:

        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.

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        • icon
          Chronno S. Trigger (profile), 9 Sep 2014 @ 9:26am

          Re: Re: Re:

          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.

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          • icon
            JF (profile), 9 Sep 2014 @ 9:36am

            Ah. 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?

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            • icon
              Chronno S. Trigger (profile), 9 Sep 2014 @ 10:29am

              Re:

              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.

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              • identicon
                Anonymous Coward, 9 Sep 2014 @ 11:02am

                Re: Re:

                Not all of them - with at least OsmAnd+ you pay once (for the app) and can download the maps for free. With its free version (OsmAnd) you can download up to 10 maps for free.

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            • icon
              John Fenderson (profile), 9 Sep 2014 @ 10:41am

              Re:

              "Why don't map apps make it easier to choose to download the maps if they work when you don't have signal?"

              Most allow you to do this pretty easily. Google maps is one of the exceptions to this -- but there are numerous alternatives.

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              • icon
                Jeremy Lyman (profile), 9 Sep 2014 @ 10:58am

                Re: Re:

                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.

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                • icon
                  John Fenderson (profile), 9 Sep 2014 @ 11:00am

                  Re: Re: Re:

                  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".

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          • icon
            Ninja (profile), 9 Sep 2014 @ 9:46am

            Re: Re: Re: Re:

            That. 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.

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          • identicon
            aerilus, 9 Sep 2014 @ 7:15pm

            Re: Re: Re: Re:

            there are two chips when smart phones first started coming out they only had agps which is assisted gps which does not receive signals from satellites just uses cell towers to tringulate. ex the first iphone. now phones have agps and real gps pretty ubiquitously. I dont know if this article is acurate I have always assumed when they talked about locating a cell phone it was triangulated. wikipedia seems to confirm this

            http://en.wikipedia.org/wiki/Assisted_GPS

            agps data is passed to e911 so i would assume it was what police use when they get a warrent in most cases. 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.

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            • icon
              John Fenderson (profile), 10 Sep 2014 @ 8:28am

              Re: Re: Re: Re: Re:

              " for most metropolitan areas I would say trigulation by cell phone is very accurate."

              You can say that, but there is no evidence that this is true and a lot of evidence that it is not. Even the law doesn't require anything like great accuracy.

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      • icon
        John Fenderson (profile), 9 Sep 2014 @ 9:11am

        Re: Re:

        Tower triangulation is never precise, but the more towers that can see the phone, the more accurate it is. 85% of all cellphones (not just smartphones) in the US currently contain a GPS chip that is used to comply with E911 requirements.

        By the way, those requirements are: carriers using 'handset based' (GPS) technology must report handset location within 50 meters for 67% of calls, and within 150 meters for 90% of calls; carriers using 'network based' (tower triangulation) technology must report location within 100 meters for 67% of calls and 300 meters for 90% of calls

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      • identicon
        Anonymous Coward, 9 Sep 2014 @ 10:35am

        Re: Re:

        GPS handset functionality depends on carrier and phone manufacturers, but in general most US carriers support GPS for mobile devices.

        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.

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  • icon
    JF (profile), 9 Sep 2014 @ 8:18am

    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.

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  • identicon
    Charles Bernardo, 9 Sep 2014 @ 8:41am

    Article in accuracies

    Possibly it would of been good to talk to a RF engineer or a carrier spokesperson on your information before printing it.

    The triangulation previously done to place analog and pre-smart phones was truly not so accurate but if you have a smartphone, either android or iphone then your phone CONTINOUSLY gives updates to the closest tower your phone location, handset signal strength and statistics on any dropped calls. These are evaluated daily by carriers to determine coverage and capacity issues.

    Federal Legislation under enhanced E-911 requires an accuracy within 100 ft of the handset.

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    • identicon
      Anonymous Coward, 9 Sep 2014 @ 9:11am

      Re: Article in accuracies

      But the high-tech evidence against her was bunk. Routinely collected tower data can place a mobile phone in a broad area, but it cannot “pinpoint” it. That would require a special three-tower “triangulation”, which cannot reveal past locations.

      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.

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      • icon
        Jeremy Lyman (profile), 9 Sep 2014 @ 10:52am

        Re: Re: Article in accuracies

        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 911 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 360 degrees of coverage, so each antenna ID corresponds to about 120 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.

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  • identicon
    Thrudd, 9 Sep 2014 @ 8:50am

    Mathematics

    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.

    As for GPS. 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.

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    • icon
      John Fenderson (profile), 9 Sep 2014 @ 10:11am

      Re: Mathematics

      "That is kyboshed to a 10 meter error by the USA"

      This hasn't been true for a few years now. Now, all of the non-receiver error is due to noise and 95% of all errors are between 0 and 10 meters. Even that error can be reduced or eliminated by using fixed groundpoints.

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  • icon
    scotts13 (profile), 9 Sep 2014 @ 8:51am

    Plea bargain system

    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.

    Yes, false information. 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.

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    • identicon
      Anonymous Coward, 9 Sep 2014 @ 8:58am

      Re: Plea bargain system

      Goes hand in hand with our guilty till proven innocent justice system.

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    • icon
      John Fenderson (profile), 9 Sep 2014 @ 10:13am

      Re: Plea bargain system

      Indeed. 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.

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    • identicon
      David, 9 Sep 2014 @ 11:53am

      Re: Plea bargain system

      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.

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      • icon
        John Fenderson (profile), 9 Sep 2014 @ 11:59am

        Re: Re: Plea bargain system

        "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."

        It's impossible to say without actually being in the situation, of course, but this wouldn't be such a slam-dunk decision for me.

        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 100 years in prison. You're pretty much done for either way.

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    • identicon
      Anonymous Coward, 9 Sep 2014 @ 1:08pm

      Re: Plea bargain system

      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.

      reply to this | link to this | view in chronology ]

  • icon
    MM_Dandy (profile), 9 Sep 2014 @ 9:12am

    GPS on phones

    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 2002 had no GPS capability whatsoever.

    reply to this | link to this | view in chronology ]

  • identicon
    Anonymous Coward, 9 Sep 2014 @ 9:56am

    just use multiple towers?

    My phone often effectively nails its location using cell towers alone (WiFi and GPS disabled). 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?

    reply to this | link to this | view in chronology ]

    • icon
      John Fenderson (profile), 9 Sep 2014 @ 10:16am

      Re: just use multiple towers?

      "Can more than one cell tower "see" a phone and its signal strength at a given time?"

      Yes, all towers that are in range of your phone has this information. 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.

      "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?"

      Technically, they could do so with greater precision than you see on your phone.

      reply to this | link to this | view in chronology ]

      • identicon
        Cell Tech, 10 Sep 2014 @ 8:26pm

        Re: Re: just use multiple towers?

        " "Can more than one cell tower "see" a phone and its signal strength at a given time?"

        Yes, all towers that are in range of your phone has this information. 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."

        Whenever a Techdirt article references cellular networks, the comments go to shit, as the clueless highlight their cluelessness. John Fenderson's comment (to pick just one) is a perfect example. *Phones* monitor signals from multiple sites and *the phones* decide when it's time to switch to another site. This is based on the received signal strength (RSSI) and the bit error rate (BER), factors which only *the phone* knows. FFS people...


        " "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?"

        Technically, they could do so with greater precision than you see on your phone."

        More than one cell tower can not see a phone at the same time, because (for most technologies) each tower is using its own TX and RX frequencies. 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. This does not provide a very detailed picture, as phones only register when they transition from one service area to another, and service areas are comprised of dozens of neighboring sites, so in the city, a phone might travel 5+ miles before reregistering, and much greater distances when outside cities. 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.

        reply to this | link to this | view in chronology ]

  • icon
    Carl "Bear" Bussjaeger (profile), 9 Sep 2014 @ 10:08am

    Cell location vs TDOA vs GPS for nontelecom types

    "Cell tower" is pretty vague. What's actually happening in cell phone location is this:

    There are three separate processes used to locate a cell phone: 1) cell (tower) the phone is connected to (I think this is what Masnick is referring to), 2) Time Difference of Arrival (TDOA) "triangulation," and GPS.

    [Many people think of "triangulation" as directional antennas being used to take bearings on a source, based on signal strength, as in seen in movies. TDOA doesn't do this because cell towers do not have moveable directional antennas (you're reasonably safe in thinking of the array as an omnidirectional antenna). TDOA simply measures the time a cell phone signal takes to reach multiple towers. All the towers have their own GPS-based synchronized timing, so they can "confer" and agree that the signal each saw was the same connection attempt from the same phone, and compute the TDOA. Time gives distance. Distance gives a circle around each tower. The phone is where the arcs intersect.]

    Number 1 is the easiest to derive (if the phone connects to the network, they perforce know what tower it's coming from), but least accurate; the phone could be anywhere in the circle area where they can get a signal.

    Number 2 is reasonably accurate to several tens of meters, which is good enough for E911 work.

    3 is quite accurate. If you have enough GPS birds in view. And you haven't had a glitch that puts you 100 kilometers off the Florida coast as you head into Chi-town.

    I think most modern smart phones incorporate GPS (some years back, a bright company finally built complete GPS receivers on a single chip), but not all phones have it, and GPS doesn't always yield a good location. Cell companies adopted TDOA location both as an interim measure before GPS-capable phones became common and as a backup to GPS.

    reply to this | link to this | view in chronology ]

  • icon
    Spaceman Spiff (profile), 9 Sep 2014 @ 10:50am

    Interesting

    Interesting that when I bring up Google Maps on my cell phone and have not enabled GPS, the circle that shows my possible location is about 1/2 mile in diameter or more (the range of the nearest cell tower)... And just how many people are in that area? I hope that woman gets a gazillion $$ from the state for her 12 years of bogus incarceration. :-(

    reply to this | link to this | view in chronology ]

    • icon
      John Fenderson (profile), 9 Sep 2014 @ 10:58am

      Re: Interesting

      That circle show the error range for your location as computed by your phone. It is not indicative of the error range for your location as computed by the telecom provider. You're comparing Granny Smith to Red Delicious.

      reply to this | link to this | view in chronology ]

  • identicon
    Rekrul, 9 Sep 2014 @ 2:12pm

    Most people are completely clueless about technology. Thanks to idiotic TV shows, people now destroy perfectly good hard drives instead of wiping them because they believe the stupid CSI shows that tell people you can never erase data off a drive.

    So does that mean that my 1TB hard drive is actually storing a perfect copy of the 20TB+ I've downloaded over the last few years? Why can't I access all that data?

    reply to this | link to this | view in chronology ]

    • identicon
      Info, 11 Oct 2015 @ 10:55am

      Re:

      because that's not how hard drives work.

      You have 1TB of data, the data you remove is flagged as available space but it is not actually removed until it is in fact overwritten with other data. Which is why you scrub mechanical drives with random data and even then you can recover some data if you're unlucky.

      That's also why the NSA and other agencies have a mechanical destruction policy on all HDD's leaving facilities after being declared unservicable.
      So all in all, i think the people doing that aren't that clueless about tech, you are.

      So to answer your questions, No it isn't storing 20TB+, it's storing whatever is flagged as writable space.

      You fill her up, remove all data (not scrub) then place 20GB on it, the remaining 980 GB still holds your previous data. Which is easily recovered by a few simple steps.

      Better way to do it is : encrypt everything on the hard drive with AES, then scrub it. and if you're really paranoid, encrypt the drive again and scrub it again.

      reply to this | link to this | view in chronology ]

  • icon
    charliebrown (profile), 9 Sep 2014 @ 7:30pm

    Vodafone Australia

    Back when I was with Vodafone, I was always on the next tower up. For example, I was in the suburb of Edmonton on the south side, connected to the White Rock tower to the north. When I went to Gordonvale, to the south, I was then connected (for the first time) to the Edmonton tower. I lived in Edmonton. Google maps https://www.google.com.au/maps/place/Edmonton+QLD+4869/@-17.0103523,145.7372872,13z/data=!3m1!4b1!4m 2!3m1!1s0x69786212a04af377:0x500eef17f210720 I was just off Mill Road.

    reply to this | link to this | view in chronology ]

  • identicon
    Anonymous Coward, 9 Sep 2014 @ 8:03pm

    This really points to a larger issue: people have this tendency to believe that technology can answer all questions.

    I want you to remember this next time you're tempted to defend techno-utopianism.

    reply to this | link to this | view in chronology ]

  • icon
    Dave Cortright (profile), 9 Sep 2014 @ 9:05pm

    My phone location ⇏ my location

    I think the bigger issue that no one seems to be talking about here is that my phone is not physically tethered to me. While I am with it much of the time, I sometimes leave it at home, in the car, at a friends, or even in a friend's car. Especially if there is no user activity on the phone, the onus is on the prosecution to prove that the phone was in fact with me at the time they claim it was in a particular area.

    reply to this | link to this | view in chronology ]

  • identicon
    jay joffe, 15 Nov 2014 @ 7:01am

    single cell tower data vs. gps

    Why wouldn't the cell tower know the distance of each client? I'm using wifi radios which are able to measure fairly precisely the distance between themselves and each attached client.

    reply to this | link to this | view in chronology ]

  • identicon
    ld, 24 Mar 2015 @ 1:36pm

    guilty

    why would you plea guilty if you are not. if i am going to fight for my innocence behind bars let me do it on an innocent plea. Maybe that is why they bluff her....ever thought of that. As far as locating using one tower i dont think its impossible i just think its not a science simply because the towers serve a more profitable purpose. Sonar does not use triangulation and is pretty precise. the same concept can be applied. People just got better thing to make money at...that's just my opinion.

    reply to this | link to this | view in chronology ]

    • icon
      nasch (profile), 24 Mar 2015 @ 2:52pm

      Re: guilty

      why would you plea guilty if you are not.

      Because innocent people get convicted, and long prison sentences are scary.

      Sonar does not use triangulation and is pretty precise.

      True, but irrelevant, since cell towers and sonar detectors don't work the same way.

      reply to this | link to this | view in chronology ]

  • icon
    bobd (profile), 17 Apr 2015 @ 9:56pm

    Why are some phones' GPS more accurate than others

    We have had several Android phones with GPS over the years, and some will be more accurate than others. I'd love to hear why, and see a review that compares accuracy of GPS across different models of phones, but I can't find that anywhere.

    We care because we have an Autistic son, and it's really important for us to be able to locate him sometimes. I need to replace his phone, and I'd like one with accurate GPS.

    reply to this | link to this | view in chronology ]

  • identicon
    ferdinand, 23 Jul 2015 @ 7:42pm

    location

    it almost went off with my conversation with my wife when i confronted with her location . she was way far from her location she said. how far does the gps gives the location of her whereabout.we live in singapore

    reply to this | link to this | view in chronology ]

  • identicon
    Brooke, 13 Oct 2015 @ 9:26am

    What is wrong

    Wonderful insights. I want to add some info that why NSA is doing this. You will be clear after reading this article written by TheOneSpy cell phone spy software. https://www.theonespy.com/what-is-wrong-about-the-nsa-tracking-the-location-of-cell-phones/

    reply to this | link to this | view in chronology ]

  • identicon
    Kim, 18 Oct 2015 @ 3:04pm

    mistaken location

    My husband tracks my location using FindmyiPhone. He has accused me of cheating on him because my phone says I am in one location when I am actually in another. I don't know how to "prove" myself.

    reply to this | link to this | view in chronology ]

    • identicon
      Mercedes, 21 Oct 2015 @ 3:56am

      Re: mistaken location

      This is happening to my daughter right now, even a private investigator says there can be no mistake but she was not at the location it says either. Might cause a divorce.How do you prove yourself

      reply to this | link to this | view in chronology ]

  • icon
    Sue (profile), 23 Nov 2015 @ 2:53am

    I am right, location lies

    I have such an issue with LOCATION/HISTORY.
    My boyfriend will ask me about a certain address and street and I am appalled by the fact he believes these stupid phone apps. Huge fights over it. I'don't like that I'may unable to prove myself to be correct. Piss on these fight starting piece of shit apps.
    But, it states location so it must be right. Bulshit.

    reply to this | link to this | view in chronology ]

  • identicon
    Anonymous Coward, 25 Jan 2016 @ 7:03am

    You guys need to Google GPS and study how the system really operates. The forth satellite is for determining time, really?!!

    reply to this | link to this | view in chronology ]

  • identicon
    Lynn Arroyo, 17 Feb 2016 @ 8:25am

    Finding location of a cell phone in a broad area

    I would love to know if there is any way for me to find out if a cell phone is, for example, located in the state of Georgia when the owner says they are in Colorado? Can anyone help?

    reply to this | link to this | view in chronology ]

    • icon
      nasch (profile), 17 Feb 2016 @ 9:36am

      Re: Finding location of a cell phone in a broad area

      I would love to know if there is any way for me to find out if a cell phone is, for example, located in the state of Georgia when the owner says they are in Colorado?

      If you're not the owner, it's unlikely you'll be able to get this information.

      reply to this | link to this | view in chronology ]

      • identicon
        Anonymous Coward, 17 Feb 2016 @ 11:54am

        Re: Re: Finding location of a cell phone in a broad area

        Thank you. No, I am not the owner, but I appreciate the answer!

        reply to this | link to this | view in chronology ]

  • icon
    nasch (profile), 29 Feb 2016 @ 10:54am

    Re: Phone was accurately tracked

    I DID have my gps navigation on at the time my phone was lost.

    That's why it could be tracked so accurately. This article is about using cell site data to locate a phone, which is less precise and less reliable.

    reply to this | link to this | view in chronology ]

  • identicon
    Melody, 26 Mar 2016 @ 7:28am

    Several years ago I called 911 in Canada. They were able to find the nearest cross roads to my location, which was only 100 metres from my position, because I did not know the name of the road I was on (I called to report a drunk driver). So this information provided here is either inaccurate or outdated.

    reply to this | link to this | view in chronology ]


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