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The reason why FM receivers are present on smartphones is that they can be used to locate your position by noting a simple thing as signal strength of transmitters. More advanced methods makes use of SNR, frequency deviation and multipath interference characteristics. And the same method can be used for WiFi which of course makes collection of such data very useful for localization purposes where GPS etc isn't useful. Arrival time of a radio signal that is reported to the operator from many devices may also be used for the same purpose.
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Smartphone with FM Radio Tells Your Position
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(Score: 2) by frojack on Thursday May 22 2014, @06:07PM
True. But "Possible" covers a wide range of supposition. It might be possible but nobody is doing this in cell phones.
It is surely "possible", and the process of using such has been recently patented [uspto.gov].
Although that patent really only covers using this as a basis to get gross location (probably 10s of miles) as an aid to guesstimating location for jump-starting Assisted GPS. Further, the patent in question contains the seeds of its own uselessness, because it specifies a network connection to the internet, and if you have that, you already have either wifi or cell towers, which are already used in Assisted GPS, and either provide more accurate information.
But the current crop of phones on the market don't have any antenna connected to the FM receiver unless you plug in your headphones, so they couldn't get a signal good enough to track anyone not having their earbuds plugged in.
FM Transmitter locations are quite well known, (and public [fmscan.org]), Nobody I've ever heard of is monitoring and timing RDS signals of FM transmitters to arrive at a time queue. So the idea of a usable time signal to calculate distance seems extremely unlikely.
That leaves relative signal strength alone, and lots of math, and a HUGE database, or an internet connection, which immediately obviates the need of FM.
Note that FM is often delivered with local repeaters expanding a market area, each with their own built in delay, and signal strength. Some of these are shared by more than one station.
No, you are mistaken. I've always had this sig.