Mobile Phone Tracking

[NickPick]

I was watching "The Bill" last night, and they showed a woman using a mobile phone tracking system to locate her son. The picture on her PC screen showed three points on a map, then drew lines from each of them to intersect at a location. When they then went to that street, there he was.

 

I thought that these tracking systems could only tell what cell the phone is currently in, which gives a location to about 100-200m. The tv picture seemed to imply that there's some direction finding equipment involved to give an exact location.

 

I know that technology in tv shows usually needs to be taken with a pinch of salt. (Tomorrows World still haven't delivered on their promise of a flying car for everyone by 2001!)

 

Does anyone have experience of these location systems? How accurate are they?

[ClanWhippy]

i used to work for a company that developed mobile phones.

 

the way it "could" theoretically be done is like this.

 

a mobile knows which base station it is "camped on" to.

it knows how strong the signal it receives is.

it also maintains a list of other base stations it can see and measures the signal strength it gets from them. this is how a mobile phone knows when to negotiate with another base station to do a handover when the phone roams from one cell to another.

 

"if" the phone sent all that data (table of base stations and signal strengths) to the network, then it would be possible to roughly triangulate it's position.

but signal strength is affected by more than just line of sight distance.

other factors include, weather, multipath (signals bouncing off buildings), electrostatically noisy environments etc.

 

this has been done in research, not sure it's ever been done in a live comercial network. although there were rumours a couple of years ago that the USA might pass a bill requiring this functionality for phones sold there.

[+The Forester]

There is another technique which some of the mobile phone tracking services use. It makes use of the fact that the turnaround time of the signal is measurable and the speed of radio waves is known.

 

Like the signal strength method, it needs the signal to be monitored by at least two (preferably three) cellular repeaters.

 

The service providers are necessarily a bit coy about making precise claims for the accuracy of such services because they are so many vagaries due to local conditions, but they don't come close to the accuracy which GPS provides.

 

The big advantage, of course, is that the position of the receiver can be measured even when the phone is indoors. Another advantage is that the phone doesn't necessarily need to be in use. Just having your mobile switched on is enough for its location to be tracked.

 

Both the Israeli and American military and security services have made extensive use of these abilities to track baddies and to "deal with" them!

 

There is also a satellite-based system which can track any moving transmitter of radio waves. It uses triplets of tethered satellites and was originally developed to track Soviet ships at sea, but nowadays has found other applications.

[+The Hokesters]

Ever heard of artistic licence?

[Deego]

Ever heard of artistic licence?

Are you saying the Bill is NOT realistic

Edited May 20, 2005 by Deego

[NickPick]

Well, I assumed it was a bit unrealistic, but it got me wondering how accurate the real systems are, and I thought who better to ask than a group of experts on various positional location systems.

 

I suppose that with the smaller cells of the 3G system, the granularity of these trackers will be improved.

 

The sat based tracking system that The Forester mentions sound a lot like the method used for tracking EPIRB emergency beacons.

[+The Hokesters]

[snip]

I thought who better to ask than a group of experts on various positional location systems.

[snip]

{Snigger, snigger} Oops sorry didn't see Forester there - I thought you were talking about us reprobates. (Deego and me )

Edited May 20, 2005 by The Hokesters

[Big Black Bunny]

Some while ago there was a proposal from Voda Phone, I think, to fit phones with a special sim card. This would enable the phone to be tracked on a mapping system like Memory Map. The idea was that companies would supply the phones to their reps. Without them being aware that they could be tracked, this way the company could check if people were where they said they were. I am not aware if this every came to fruition, but it would indicate that even several years ago it was possible.

[+JUSTHEJOB]

Hi Have you tried the mobile phone tracking service FollowUs

Edited May 20, 2005 by JUSTHEJOB

[+Teuchters]

There are various phone location systems.

One basic method will only tell you which mast has picked up the signal. The actual phone could be many miles from this.

Other systems have built in GPS technology which may be used by some organisations (vehicle recovery companies and roadside assistance) so you don't have to tell them where you have broken down.

[+The Forester]

The sat based tracking system that The Forester mentions sound a lot like the method used for tracking EPIRB emergency beacons.

Not quite.

 

The tethered triplet satellites work on a quite different principle. They fly in an L-shaped formation and compare the phase of arriving radio wave sources. Because their spatial relationship to eachother is known to a very high degree of accuracy, it is a geometrically simple matter to calculate the relative 3-D co-ordinates of the source of the radio emitter. If, let's say, satellite B of the formation is the first the receive the radiowave then the source must be nearest to its position. Satellite A, let's say, receives it next and from that data two possible 2-D co-ords on the surface of the Earth can be deduced. Then, let's say, satellite C of the formation receives the wavefront, so the system can immediately determine which side of the baseline between A & B the signal source is located. Assuming the signal source is on the surface of the Earth, a full 3-D fix can thus be made instantaneously.

 

That is only one of half a dozen different methods of position fixing by satellite.

 

The Search And Rescue Satellite (SARSAT) systems use two other methods. One which is used by the Global Maritime Distress Surveillance System is simply to listen to the GPS derived co-ordinates which are transmitted by a vessel in distress.

 

Another method, also used by some elements of GMDSS, is an inverse of the old Transit Doppler system which was the US Navy's forerunner to the USAF NavStar GPS. This is what is used to measure the position of a typical EPIRB or SARBE or TACBE. (Sorry 'bout the FLAs!)

 

It works by the satellite monitoring the frequency shift of the surface transmitted signal, rather like listening to the changing pitch of the sound of a siren on a police car whizzing past you. It's not particularly accurate on a single satellite pass, but good enough to dispatch rescue services to a location within a mile or two of a maritime accident scene while further fixes are taken by subsequent satellite passes to refine the fix. The same priciple is used all the time to monitor the location of teenyweeny beacons attached to wildlife such as reindeer, whales, and even ospreys. This system is sometimes mistaken by ignorami as being GPS. Although it is satellite position fixing, it is not GPS.

 

GPS, in its NavStar incarnation, has three or four different methods of position fixing. The one which we benefit from in geocaching is called pseudoranging. Another method of position fixing which we can use with civilian receivers is phase measurement, which uses a similar method to the tethered triplet satellites which I mentioned, but does it from the ground upwards and then back-calculates the ground position in post-processing and is therefore not useable in practical geocaching - at least not when searching for a cache.

 

Cheers, The Forester

[+badger]

This site may offer someting similar to the system on The Bill.

Child Mobile Tracking

 

They claim 150m accuracy...

 

Matt

[+sTeamTraen]

They claim 150m accuracy...

That's handy. So you know your teenager is either at their karate class, or down the pub. Most reassuring.

[+Sensei TSKC]

Oss!

[NickPick]

They claim 150m accuracy...

That's handy. So you know your teenager is either at their karate class, or down the pub. Most reassuring.

Or in the pub next door to their Karate class.