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> Is anyone working on something better than signal strength triangulation for cell tower based positioning? First, cell towers do better than mere signal stre

by lutusp 13y ago

> Is anyone working on something better than signal strength triangulation for cell tower based positioning? First, cell towers do better than mere signal strength triangulation -- they use signal arrival time and round-trip time to get a pretty good fix on a phone's location. Not nearly as good as GPS, but reasonably good. Second, smartphones have GPS receivers, and some of those allow the GPS position to accompany the outgoing call. That's much better, but it sometimes requires that the call be placed outdoors. I think in the future, all cell phones will have GPS, and a few other improvements will come along to allow much better positioning.

modeless 13y ago
>they use signal arrival time and round-trip time Do you have a source for this? As far as I know this is not true. They use signal strength and knowledge of cell tower antenna locations, but not time of flight of the radio signal, as GPS does.
- lutusp 13y ago
  Just a handful, and most of them are pretty vague: http://en.wikipedia.org/wiki/Mobile_phone_tracking http://en.wikipedia.org/wiki/Mobile_phone_tracking Quote: "Using the SIM in GSM and UMTS handsets, it is possible to obtain raw radio measurements from the handset.[6][7] The measurements that are available can include the serving Cell ID, round-trip time, and signal strength. " http://wrongfulconvictionsblog.org/2012/06/01/cell-tower-triangulation-how-it-works/ http://wrongfulconvictionsblog.org/2012/06/01/cell-tower-tri... Quote: "Within each sector, the tower can make a measurement of how far away the transmitting cell phone is. This is done by measuring signal strength and the round-trip signal time." Neither of the above references is very specific, but I recently read a paper that went into great detail, and showed graphs of the areas with the greatest accuracy, all based on arrival time measurements. Some of it may have been speculative based on future improvements in the system. But I can't locate that specific paper. Here's another reference: http://www.cnet.com/news/feds-push-for-tracking-cell-phones/ http://www.cnet.com/news/feds-push-for-tracking-cell-phones/ Quote: "T-Mobile, for instance, uses a GSM technology called Uplink Time Difference of Arrival, or U-TDOA, which calculates a position based on precisely how long it takes signals to reach towers. A company called TruePosition, which provides U-TDOA services to T-Mobile, boasts of "accuracy to under 50 meters" that's available "for start-of-call, midcall, or when idle."" You know, now that I've read these articles, it sounds more like a future technology than something that's in place right now, except for a few networks.
  - modeless 13y ago
    Awesome, thanks for the pointers! I've had difficulty finding information about this in the past. In particular, U-TDOA and TruePosition looks like exactly what I've been wanting. http://www.trueposition.com/about-trueposition/resource-center/white-papers/trueposition-guide-to-location-technologies/DownloadSecured http://www.trueposition.com/about-trueposition/resource-cent... Accuracy of 50 meters is a bit disappointing, but hopefully the technology has room to improve. It's also disappointing that they're focused on the benefits for law enforcement and carriers rather than handset makers and end users.
    - lutusp 13y ago
      > It's also disappointing that they're focused on the benefits for law enforcement and carriers rather than handset makers and end users. That's just politics. The cell carriers know they need to get regulatory approval from government agencies before they begin to sell the technology to the public. That regulatory approval is more likely if they can show a governmental advantage, like pinning down the location of a drug dealer or a terrorist chatting on his cell phone. The real advantage for the carriers, by the way, is they can make a planned tower switch for a moving phone more accurately if they have both position and velocity information. It's hard to get a velocity vector if you can't resolve a position to better than 3/4 mile, what you get with signal strength measurements and no time-of-flight. (The Doppler effect could provide velocity as well, but without a very good direction of motion.)

by lutusp 13y ago

modeless 13y ago

>they use signal arrival time and round-trip time Do you have a source for this? As far as I know this is not true. They use signal strength and knowledge of cell tower antenna locations, but not time of flight of the radio signal, as GPS does.

lutusp 13y ago
Just a handful, and most of them are pretty vague: http://en.wikipedia.org/wiki/Mobile_phone_tracking http://en.wikipedia.org/wiki/Mobile_phone_tracking Quote: "Using the SIM in GSM and UMTS handsets, it is possible to obtain raw radio measurements from the handset.[6][7] The measurements that are available can include the serving Cell ID, round-trip time, and signal strength. " http://wrongfulconvictionsblog.org/2012/06/01/cell-tower-triangulation-how-it-works/ http://wrongfulconvictionsblog.org/2012/06/01/cell-tower-tri... Quote: "Within each sector, the tower can make a measurement of how far away the transmitting cell phone is. This is done by measuring signal strength and the round-trip signal time." Neither of the above references is very specific, but I recently read a paper that went into great detail, and showed graphs of the areas with the greatest accuracy, all based on arrival time measurements. Some of it may have been speculative based on future improvements in the system. But I can't locate that specific paper. Here's another reference: http://www.cnet.com/news/feds-push-for-tracking-cell-phones/ http://www.cnet.com/news/feds-push-for-tracking-cell-phones/ Quote: "T-Mobile, for instance, uses a GSM technology called Uplink Time Difference of Arrival, or U-TDOA, which calculates a position based on precisely how long it takes signals to reach towers. A company called TruePosition, which provides U-TDOA services to T-Mobile, boasts of "accuracy to under 50 meters" that's available "for start-of-call, midcall, or when idle."" You know, now that I've read these articles, it sounds more like a future technology than something that's in place right now, except for a few networks.
- modeless 13y ago
  Awesome, thanks for the pointers! I've had difficulty finding information about this in the past. In particular, U-TDOA and TruePosition looks like exactly what I've been wanting. http://www.trueposition.com/about-trueposition/resource-center/white-papers/trueposition-guide-to-location-technologies/DownloadSecured http://www.trueposition.com/about-trueposition/resource-cent... Accuracy of 50 meters is a bit disappointing, but hopefully the technology has room to improve. It's also disappointing that they're focused on the benefits for law enforcement and carriers rather than handset makers and end users.
  - lutusp 13y ago
    > It's also disappointing that they're focused on the benefits for law enforcement and carriers rather than handset makers and end users. That's just politics. The cell carriers know they need to get regulatory approval from government agencies before they begin to sell the technology to the public. That regulatory approval is more likely if they can show a governmental advantage, like pinning down the location of a drug dealer or a terrorist chatting on his cell phone. The real advantage for the carriers, by the way, is they can make a planned tower switch for a moving phone more accurately if they have both position and velocity information. It's hard to get a velocity vector if you can't resolve a position to better than 3/4 mile, what you get with signal strength measurements and no time-of-flight. (The Doppler effect could provide velocity as well, but without a very good direction of motion.)