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'[OT]:cell phone locating'
2001\09\13@165059 by Alice Campbell

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Some months ago there was a thread on jamming cell phones.  Now I am wondering how to get the spatial coordinates of a given cell phone.  Is it technically feasible to identify a single cell phone from a satellite or other high point?

Maybe you can guess what I'm wondering.

alice
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2001\09\13@170516 by David VanHorn

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At 04:49 AM 9/14/01 +0800, Alice Campbell wrote:
>Some months ago there was a thread on jamming cell phones.  Now I am
>wondering how to get the spatial coordinates of a given cell phone.  Is it
>technically feasible to identify a single cell phone from a satellite or
>other high point?
>
>Maybe you can guess what I'm wondering.

Very very rough.

A doppler DF unit, or portable TDOA, with a relatively deaf receiver, could
be used to find a given cell phone.

You'd need a receiver that it is illegal for "us guys" to buy, because the
only practical way to identify a given signal is by listening to it.

The environment however, is rife with reflections, so you'd need a crew of
experienced foxhunters to work the gear.

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2001\09\13@171623 by Ian Jordan

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I would think that the answer would be no. There really is no way to know
the altitude of a cell phone from above, and without the altitude data, any
angle that the satellite had on looking down at the target would cause a
very big error as to location. If you were directly above then altitude not
a factor, but then again, if you're directly above you already know where
the target signal is, right?

However, three cell sites on the ground should give you a very nice fix, but
without the altitude. 4 sites give you altitude nicely. This is one of the
ways that the new E-911 services will/do work. But remember, overall, cell
phones aren't even really designed to work above the ground or at 500+ MPH.
I am pretty amazed that any calls got through.

--Ian

{Original Message removed}

2001\09\13@171633 by Don Hyde

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The cell phone industry is currently fighting with the FCC over "E911",
which would add extra equipment to either cell phone base stations or the
cell phone handsets or both, which would make it possible to locate a cell
phone making a 911 call.

There are technical and economic problems i.e. getting it to work and paying
for it, but underlying all the fighting is the fear that it would work all
the time.  Cell phones are constantly communicating with base stations even
when you are not talking.  That's how the network knows how to find your
cellphone for an incoming call.

If it works all the time, then there is a permanent subpoena-able record of
your every movement whenever you had your cell phone turned on.  Bad guys
might hack the system and be able to track you.  Divorce attorneys would
certainly subpoena such records.  Business rival's attorneys might cook up a
lawsuit so that they could subpoena such records.  It could be a great boon
for stalkers, assassins and papparazzi, as well as burglars.

Federal courts have already ruled that the FBI could collect such data
without a search warrant, since it would not involve entering anyone's home,
and would be legally treated as 'traffic analysis' which does not constitute
a phone tap.  It would require only a single blanket court order to monitor
all phones in the country.

Could such a system help police find some bad guys?  Sure.  Bad guys would
also be able to find all of us, too.  Don't forget that some of the police
are bad guys, or are in the pay of bad guys.  That's why we have search
warrants and Miranda and such.

> {Original Message removed}

2001\09\13@171948 by jamesnewton
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It is certainly technically possible to know the cell that the phone is in..
..but that won't help put survivors out of the rubble.

I would guess that a triad of rotating unidirectional antennas with a
receiver slaved to the cell frequency of the desired phone (how do you get
that info?) which then record peaks and report them along with the degree of
rotation at the peak point to a computer that then triangulates and plots
the intersection?

That might be something worth developing in time for the next emergency...

...long ago, I discussed an RF locator tags that remain dormant until
activated by an external pulse and which would then re-transmit the pulse at
a different frequency to assist in locating persons or property. The point
was that you can make the tags for next to nothing and hide them in jewelry,
glasses, keys, wallets, shoes, etc...

Think of the benefit to Fire departments, SAR, SWAT, INS, campers, parents,
etc.

Of course it does nothing for the grinding effect of the concrete or the
deceleration trauma when you are in a building that is falling down...

...anyone care to develop a collapse proof armored suite for the hi-rise
office worker?

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{Original Message removed}

2001\09\13@173037 by t F. Touchton

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part 1 3394 bytes content-type:text/plain; charset=us-ascii
Check out http://www.trueposition.com.

Scott F. Touchton
1550 Engineering Manager
JDS Uniphase



                   Don Hyde
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The cell phone industry is currently fighting with the FCC over "E911",
which would add extra equipment to either cell phone base stations or the
cell phone handsets or both, which would make it possible to locate a cell
phone making a 911 call.

There are technical and economic problems i.e. getting it to work and
paying
for it, but underlying all the fighting is the fear that it would work all
the time.  Cell phones are constantly communicating with base stations even
when you are not talking.  That's how the network knows how to find your
cellphone for an incoming call.

If it works all the time, then there is a permanent subpoena-able record of
your every movement whenever you had your cell phone turned on.  Bad guys
might hack the system and be able to track you.  Divorce attorneys would
certainly subpoena such records.  Business rival's attorneys might cook up
a
lawsuit so that they could subpoena such records.  It could be a great boon
for stalkers, assassins and papparazzi, as well as burglars.

Federal courts have already ruled that the FBI could collect such data
without a search warrant, since it would not involve entering anyone's
home,
and would be legally treated as 'traffic analysis' which does not
constitute
a phone tap.  It would require only a single blanket court order to monitor
all phones in the country.

Could such a system help police find some bad guys?  Sure.  Bad guys would
also be able to find all of us, too.  Don't forget that some of the police
are bad guys, or are in the pay of bad guys.  That's why we have search
warrants and Miranda and such.

> {Original Message removed}
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part 3 105 bytes
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2001\09\13@174313 by Chris Carr

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> Some months ago there was a thread on jamming cell phones.  Now I am
wondering how to get the spatial coordinates of a given cell phone.  Is it
technically feasible to identify a single cell phone from a satellite or
other high point?
>
The short answer is yes the maths are fairly well established, multiple
satellites are better, for either you have to add a great number of
qualifiers (which equates to unlimited amounts of money)

> Maybe you can guess what I'm wondering.
>
No, I don't speculate on non-engineering matters if sufficient negotiable
currency is put in my
bank account. 8-)

Regards
Chris Carr


P.S. If you haven't twigged by now, I have a sick sense of humour. However,
my first comment was genuine.

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2001\09\13@183304 by Barry Gershenfeld

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>Some months ago there was a thread on jamming cell phones.  Now I am
wondering how to get the spatial coordinates of a given cell phone.  Is it
technically feasible to identify a single cell phone from a satellite or
other high point?
>
>Maybe you can guess what I'm wondering.

Hmm, you're looking for a white Ford Bronco?

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2001\09\13@193211 by Jim

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    "I am pretty amazed that any
     calls got through."

I guess I am the only one that picked up
the fact from a couples of interviews with one
of the recipients of those calls a day ago that
*those* two partys used the *Airphone* service
aboard the aircraft to make the call. In fact,
Alice Hoglan corrected the interviewer (once
that I saw) and said she used the 'Airphone'
service.

I suspect that was the case in several of other
instances as well, but all you hear from the
press (and posters on most boards) is 'cell phone'.

It also grinds me when these same script-readers
refer to CVRs and FDRs as 'black boxes' ...

Jim



{Original Message removed}

2001\09\13@193644 by Jim

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   "Cell phones are constantly communicating
    with base stations even when you are not
    talking."

"Autonomous Registration" in my market (IS-136, TDMA)
is currently set to every 10 minutes. It was that way
when I was still with ATTWS in '96. This is verifiable
by placing an RF detector (or simply an AM radio) next
to an idle phone and taking note the clicks or RF
indication.

Re-registration also takes place when you move
from your present cell -the phone will take a
look at new candidate control channels, find
a suitable candidate, then attempt a registration
letting the MTSO (the 'switch' or HLR) know what
cell you're now in.

There is also power-up and power-down registrations
as well ...


Jim


{Original Message removed}

2001\09\13@193848 by Dan Michaels

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At 02:17 PM 9/13/01 -0700, you wrote:
>I would think that the answer would be no. There really is no way to know
>the altitude of a cell phone from above, and without the altitude data, any
>angle that the satellite had on looking down at the target would cause a
>very big error as to location. If you were directly above then altitude not
>a factor, but then again, if you're directly above you already know where
>the target signal is, right?
>
>However, three cell sites on the ground should give you a very nice fix, but
>without the altitude. 4 sites give you altitude nicely.
...........


Why not 3 or 4 satellites in low-earth orbit? Precise clocks,
sophisticated RF front-ends.









This is one of the
>ways that the new E-911 services will/do work. But remember, overall, cell
>phones aren't even really designed to work above the ground or at 500+ MPH.
>I am pretty amazed that any calls got through.
>
>--Ian
>
>{Original Message removed}

2001\09\13@195528 by Jim

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   "the only practical way to identify a
    given signal is by listening to it."

This was true in the days of analog only 800 MHz
cellular - but those days are long gone for the
majority of users today ... where today the mode of
choice is digital (GREATLY increases the capacity of
the fixed infrastructure operator plus a number of
benefits such as security and data can be supported
as well). Then there is the problem that digital
comes in one bascially one of three flavors (given
two 800 MHz operators and at least 3 1800 MHz
operators that I'm aware of):

1) TDMA (IS-136 et al) 2) TDMA (GSM) and 3) CDMA (IS-95 et al)

Then there is WCDMA and GPRS just waiting in the wings ...

Jim



{Original Message removed}

2001\09\13@200841 by Ian Jordan

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I had noticed that the Airphone system was, in fact, used in many of these
calls. However, there is at least one that came from the bathroom of one of
the planes, on a cell phone for sure. Even called the local 911 from what I
have heard, which I really doubt the airphone system would route you to.

--Ian

{Original Message removed}

2001\09\13@200901 by John Ferrell

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For those who may not be aware:

We dog lovers use a product that consists of a "microchip" that is imbedded
in the shoulder of our precious animals. This allows the positive
identification of animals that have lost their collars and external
identification. The program is sponsored by the American Kennel Club (AKC)
which uses part of the revenue to provide the necessary scanners to animal
control agencies across the country.  I don't recall the cost of the device
to us users, but it did not seem relevant at the time. Inserting the chip is
done with a large gauge needle that is best done under anesthetic. Typically
it is done concurrent with other medical procedures.  Unfortunately, animal
shelters sometimes euthanize a lost animal without testing for the microchip
identity in spite of the fact that the equipment is provided to them at no
cost.

Of course there are risks of misuse for this kind of technology  with people
but it is out there and it works. I would think a similar device could be
developed simply for locating individuals.  I will refrain from comment on
the need for this technology.


John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"



----- Original Message -----
From: "James Newton. Admin 3" <RemoveMEjamesnewtonTakeThisOuTspamPICLIST.COM>
To: <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Thursday, September 13, 2001 5:18 PM
Subject: Re: [OT]:cell phone locating


> It is certainly technically possible to know the cell that the phone is
in..
> ..but that won't help put survivors out of the rubble.
>
> I would guess that a triad of rotating unidirectional antennas with a
> receiver slaved to the cell frequency of the desired phone (how do you get
> that info?) which then record peaks and report them along with the degree
of
> rotation at the peak point to a computer that then triangulates and plots
> the intersection?
>
> That might be something worth developing in time for the next emergency...
>
> ...long ago, I discussed an RF locator tags that remain dormant until
> activated by an external pulse and which would then re-transmit the pulse
at
> a different frequency to assist in locating persons or property. The point
> was that you can make the tags for next to nothing and hide them in
jewelry,
> glasses, keys, wallets, shoes, etc...
>
> Think of the benefit to Fire departments, SAR, SWAT, INS, campers,
parents,
{Quote hidden}

> {Original Message removed}

2001\09\13@200925 by David VanHorn

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At 06:54 PM 9/13/01 -0500, Jim wrote:
>     "the only practical way to identify a
>      given signal is by listening to it."
>
>This was true in the days of analog only 800 MHz
>cellular - but those days are long gone for the
>majority of users today ... where today the mode of
>choice is digital (GREATLY increases the capacity of
>the fixed infrastructure operator plus a number of
>benefits such as security and data can be supported
>as well). Then there is the problem that digital
>comes in one bascially one of three flavors (given
>two 800 MHz operators and at least 3 1800 MHz
>operators that I'm aware of):
>
>1) TDMA (IS-136 et al) 2) TDMA (GSM) and 3) CDMA (IS-95 et al)
>
>Then there is WCDMA and GPRS just waiting in the wings ...


Well, if you can propose a simple way to pick out a given phone, I'd like
to hear it.
Otherwise, you're stuck with numbing the receiver till all it can pick up
is the nearest source.
A differential FSM is what you end up with.  This is more useful than you
might think, since it works better the closer you get.

--
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2001\09\13@202419 by Ian Jordan

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Sure, but the question seemed to be if *one* satellite could do it. Maybe I
mis-interpreted the question.

Also- how well does 1 or 2 GHz travel through the atmosphere? You would need
a very sensitive front-end on that satellite. If you're gonna do this, why
not do it with all the nice receivers we already have on the ground?

--Ian


> Why not 3 or 4 satellites in low-earth orbit? Precise clocks,
> sophisticated RF front-ends.

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2001\09\13@203044 by Jim

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  "at least one that came from the bathroom
   of one of the planes,"

I was aware of that particular call ... as reported
by the *news* media of course!

Jim


{Original Message removed}

2001\09\13@203533 by Ian Jordan

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I'm not familiar with "TDOA" - what is it?

My assumption is that the system knows how far away the cell phone is from
each tower. So:
One cell tower gives you a sphere on which the cell phone could lie.
Two towers give you a "box" where the cell phone could be, of which two
points are on the surface of the earth.
Three towers give you one deterministic point on the earth.
A fourth tower gives you a deterministic point in all space, including
altitude.

I can't remember if the third gives you altitude or not, but I'm pretty sure
that two towers give you two points, both of which are on the surface of the
earth and you have no way of knowing which is which, hence the need for a
third tower, satelite, or whatever.

Am I missing some bit of data that allows you to eliminate one of the two
points in a two-tower system?

--Ian


> Three - why does one need three when using 2 and TDOA
> will work for position on a geometrical plane? Well,
> solving for 'elevation' I suppose is a goal/reason for
> using three ...

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2001\09\13@205118 by Jim

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----- Original Message -----
From: "Ian Jordan" <RemoveMEianEraseMEspamEraseMETWINGLES.COM>
To: <RemoveMEPICLISTspam_OUTspamKILLspamMITVMA.MIT.EDU>
Sent: Thursday, September 13, 2001 7:23 PM
Subject: Re: [OT]:cell phone locating


> Sure, but the question seemed to be if *one* satellite could do it. Maybe
I
> mis-interpreted the question.
>

With one sat you only get a bearing using the received
angle of the signal - and this can be done one of several
ways - but the accuracy at several hundred miles (angular
resolution wise) is going to be poor and yield little
with which to work with.


> Also- how well does 1 or 2 GHz travel through the atmosphere? You would
need

GPS does it every day.

> a very sensitive front-end on that satellite. If you're gonna do this, why
> not do it with all the nice receivers we already have on the ground?

That's the *way* it's going to be done - for a number
of reasons - not the least of which is that *frequency
resuse* in a mature system kinda dictates that you use
the system infrastructure (existing antennas, multicouplers,
T-spans) that views only the area it's been designed to
'cover' RF-wise.

In an N=7 frequency resuse plan - a "cookie cutter" is
composed of 7 different frequency groups - and the system
is then quite literally "cut out" with this cookie cutter
and you end up with frequencies in the system being reused
a specific distance away (depending on a few factors) based
in part on how artful one is at juggling with the "frequency
plan" in a discrete-frequency system (as TDMA is compared
to CDMA) and what level of "co-channel" interference
you are willing to live with ...

Jim



Jim

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2001\09\13@210033 by Jim

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----- Original Message -----
From: "Ian Jordan" <RemoveMEianKILLspamspamTWINGLES.COM>
To: <PICLISTSTOPspamspamspam_OUTMITVMA.MIT.EDU>
Sent: Thursday, September 13, 2001 7:36 PM
Subject: Re: [OT]:cell phone locating


> I'm not familiar with "TDOA" - what is it?

Time Difference Of Arrival. Key off a particular
*known* sylable (or with digital - the digi info)
and measure the time difference as received at each
site.


>
> My assumption is that the system knows how far away the cell phone is from
> each tower. So:

Well, there is a TA (Time Alignment) value that each TDMA
phone is given - depending on where in it's signal is arriving
at the receiver in it's assigned time slot - but this is a
very course value ...


> One cell tower gives you a sphere on which the cell phone could lie.

How is this being measured - AOA (Angle of Arrival?)

> Two towers give you a "box" where the cell phone could be, of which two

Two (or more) and you have isolated a 'point' where the phone
should lie (angele accuracy presents a small error factor, as
will reflections from buildings, structures, etc)

TDOA is usasble with 2, or more, as well.

> points are on the surface of the earth.
> Three towers give you one deterministic point on the earth.
> A fourth tower gives you a deterministic point in all space, including
> altitude.

Solve for 3 (or more) and another "distance line" can
be calculated - this (all 3) could be used to solved
for an elevation figure ...

I think studying what GPS does at this point would be
a good idea ... I haven't done a whole lot of study on
some of the finer points on cellular RDF to go in-depth
off the top of my head (and not start spouting untruths!) -
- on a slighty different note, Ericsson recently (this
year) made an announcement on an aggreement with a
company regarding the use of TDOA as their choice
for a system to achieve E911 capability ...

Jim

>
> I can't remember if the third gives you altitude or not, but I'm pretty
sure
> that two towers give you two points, both of which are on the surface of
the
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2001\09\13@220529 by Ian Jordan

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Yeah, but with a transmitter that is a bit more than the max of .6W (50W for
GPS) from a PCS phone, and with an antenna that is not omnidirectional..

> > Also- how well does 1 or 2 GHz travel through the atmosphere? You would
> need
>
> GPS does it every day.
>

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2001\09\14@013400 by David VanHorn

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At 05:36 PM 9/13/01 -0700, Ian Jordan wrote:
>I'm not familiar with "TDOA" - what is it?

Time Difference of Arrival

You switch between a pair of antennas, and this phase modulates the signal.
Synchronus detection then picks off the signal, and recovers the direction
information.

>My assumption is that the system knows how far away the cell phone is from
>each tower.

It dosen't



> > Three - why does one need three when using 2 and TDOA
> > will work for position on a geometrical plane? Well,
> > solving for 'elevation' I suppose is a goal/reason for
> > using three ...

I was figuring this as a hand-held unit, where elevation would be solved by
walking around.

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2001\09\14@042244 by Bond, Peter

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> It is certainly technically possible to know the cell that
> the phone is in..
> ..but that won't help put survivors out of the rubble.

There is a method under GSM that can triangulate without additional kit
(lots of additional SW, though) - but I don't think it was any more accurate
than about a 50m radius, so would be of limited use here.  Motorola were
looking at it, but persuading operators to pay for it was tricky IIRC.

> ...long ago, I discussed an RF locator tags that remain dormant until
> activated by an external pulse and which would then
> re-transmit the pulse at
> a different frequency to assist in locating persons or
> property. The point
> was that you can make the tags for next to nothing and hide
> them in jewelry,
> glasses, keys, wallets, shoes, etc...

As seen on Tomorrow's World (BBC TV kiss of death to any hi-tech idea) a
number of years ago for skiers - powered by the RF from the search units,
would retransmit to alert searchers.  Also proposed in Walter Jon Williams'
"Hardwired" - but that was smart chaff (don't suppose anyone has a spare
copy of that, do they...?)

Peter
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2001\09\14@071209 by Peter L. Peres

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> Some months ago there was a thread on jamming cell phones.  Now I am
> wondering how to get the spatial coordinates of a given cell phone.
> Is it technically feasible to identify a single cell phone from a
> satellite or other high point?
>
> Maybe you can guess what I'm wondering.
>
> alice

I have no idea why you are wondering but you can consider a digital GSM
phone as a 0.6W (at most) digital isotropical transmitter for most
purposes, and apply that to the radio link equation. You will end up with
a pretty big antenna to receive it at some distance (like 10 miles).
Normal cell tower antennas are approx. 1.2 x 0.4 meters in dimensions,
with a dielectric lens that also serves as radome. The lens gives wide
coverage (135 degrees or so usually).

You can probably use one with a narrow lens mounted on an azimuth bearing
on the roof of a small truck or van to get a bearing, using a band imaging
receiver. By moving the truck and getting a second bearing you could get a
fix on a location. I guess it would take a 5 minute transmission and a
300ft base to get a reasonable fix in urban conditions at close range.

This would still not tell height or depth. Maybe the antenna could be
swiveled to get a vertical angle bearing to judge height or depth.
Basically it would have to be gymballed, maybe in a gymbal meant for a
large spotlight.

I think that such antennas can be ordered ready made from cell equipment
makers. Figure up to $4000 or so for the antenna alone (it usually has
attached electronics), but I am sure they would donate one for a good
purpose.

I think that is is more interesting at the moment to locate a phone at
short distance (f.ex. in rubble). Also pagers/voice mail originators
(PDAs SMS etc).

Peter

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2001\09\14@074001 by Peter L. Peres

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> Why not 3 or 4 satellites in low-earth orbit? Precise clocks,
> sophisticated RF front-ends.

Because the cells have too little power spread over too much bandwidth and
you need gigantic antennas to hear them probably. Remember that max power
is 0.6W into an antenna with 0dB or worse gain, and the antenna does not
have an up-pointing lobe probably. The last time I checked amateur
satellite issues you needed 20W into a good directional cross-polarized
Yagi with 30+dB gain with 3 kHz bw (AMTOR or PACTOR or what over SSB) to
get through for a few minutes in an overflight. The cell phone has less
power, more bandwidth and a piss poor antenna. I don't think that it will
make it. What is the power and bandwidth of EPIRB beacons ? (I remember
something like 5W into a good antenna with a good counterweight - the
ocean or a ship's steel body - and narrow bandwidth - wrong ?).

Peter

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2001\09\14@075100 by Peter L. Peres

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> Time Difference Of Arrival. Key off a particular
> *known* sylable (or with digital - the digi info)
> and measure the time difference as received at each
> site.

It is not necessary to key a known dataset. Only the receivers need to
have accurate clocks and timestamp a sample of some length. Then the
samples are transmitted somewhere else and processed for correlation. It
is very easy. The problem is the resolution depends on the channel
bandwidth exactly like in radar. With a cell phone channel I doubt whether
it can be gotten under 300 meters easily. Even 100 square meters is a lot
of digging if you are looking for someone under rubble.

I think that calling the caller back to obtain a longer transmission and
using a handheld switched dipole type TDOA (foxhunt type)  will yield
better results at shorter distances. I think that cell phones of the poor
buried people are more likely to be still operational than their owners,
even though too much time has passed by now and most batteries must have
run down.

Peter

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2001\09\14@092702 by Jim

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His question was: "how does a 1 or 2 GHZ signal travel" -

NOT: "what would the path-loss be at 1 or 2 GHz" ...

Jim



{Original Message removed}

2001\09\14@100222 by Jim

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----- Original Message -----
From: "Peter L. Peres" <@spam@plp@spam@spamspam_OUTACTCOM.CO.IL>
To: <spamBeGonePICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Friday, September 14, 2001 7:06 AM
Subject: [OT]:cell phone locating


{Quote hidden}

Ten miles is actually a pretty easy path - unless you're
trying to "work through dirt" or a lot of urban buildings.
I regularly work these distances at UHF with a .5 Watt UHF
radio ...

> Normal cell tower antennas are approx. 1.2 x 0.4 meters in dimensions,
> with a dielectric lens that also serves as radome. The lens gives wide
> coverage (135 degrees or so usually).

Most of those 'covers' are only 'covers' - within you will find
a variety of either dipoles, patch antennas, etc coupled together
with a phasing harnesses ...

>
> You can probably use one with a narrow lens mounted on an azimuth bearing
> on the roof of a small truck or van to get a bearing, using a band imaging

At these frequencies - and-held yagis are MOST suitable ...


> receiver. By moving the truck and getting a second bearing you could get a
> fix on a location. I guess it would take a 5 minute transmission and a

I have chased down "un-cooperative" sources as a matter of tracking
down RFI (Innterference) sources. With a little practice, you'd be
surprised at what you can do ...

{Quote hidden}

Wha?  Sounds like an integrated cell site or a remote duplexer/power
amp combo. Most of these 'antennas' alone are 1/4 that price ...

> purpose.
>
> I think that is is more interesting at the moment to locate a phone at
> short distance (f.ex. in rubble). Also pagers/voice mail originators
> (PDAs SMS etc).

I have tracked down 'active antennas' that oscillate and sweep through
the UHF amatuer band - models like the Radio Shack ATV-1000, a set-top
model. One that was giving me trouble was just under a mile away ...
these things radiate at low power - no where near the max. power output
of .6 watts at power level 3 of a cell phone.

Jim


>
> Peter
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2001\09\14@101630 by Jim

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----- Original Message -----
From: "Peter L. Peres" <.....plpspam_OUTspamACTCOM.CO.IL>
To: <TakeThisOuTPICLIST.....spamTakeThisOuTMITVMA.MIT.EDU>
Sent: Friday, September 14, 2001 7:36 AM
Subject: Re: [OT]:cell phone locating


> > Why not 3 or 4 satellites in low-earth orbit? Precise clocks,
> > sophisticated RF front-ends.

Front ends? Like those employing PHEMT GaAs FETs?  Easy to do ...

>
> Because the cells have too little power spread over too much bandwidth and

Are we talking downlink from the cell site here - or uplink
from the subscriber's (phone) handset?

> you need gigantic antennas to hear them probably. Remember that max power
> is 0.6W into an antenna with 0dB or worse gain, and the antenna does not
> have an up-pointing lobe probably. The last time I checked amateur

With an antenna comprised of no more than a dipole - the pattern
from an antenna of that type is extremely broad. Thefore a portion
of the 'lobe' is off into space.

> satellite issues you needed 20W into a good directional cross-polarized
> Yagi with 30+dB gain with 3 kHz bw (AMTOR or PACTOR or what over SSB) to

Cross-polarzed yagis yield 30 dB of gain? I could buy something on the
order of 12 dB - but not 30 Peter!


> get through for a few minutes in an overflight. The cell phone has less
> power, more bandwidth and a piss poor antenna. I don't think that it will

I guess no consideration is given to the item required/that would be
used in space to make up for the low phone output power and path
loss - *this* is where your 30 dB antenna comes into play ... now I'm
not saying that a .6 watt GSM phone can be picked up by a LEO sat in
space under *any* conditions - I haven't run the numbers on that
scenario ...


> make it. What is the power and bandwidth of EPIRB beacons ? (I remember
> something like 5W into a good antenna with a good counterweight - the
> ocean or a ship's steel body - and narrow bandwidth - wrong ?).

And what freq range do those beacons operate in? Are the antennas
used on the satellites to receive those EPIRBS omni or directional?

I suspect omni and not directional - that means low gain - so the
path loss is made up by higher output required of the EPIRB (again,
I haven't run the PL calcs).

Jim

>
> Peter
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2001\09\14@124605 by Jim

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    "Well, if you can propose a simple way
     to pick out a given phone, I'd like
     to hear it."

Sure ...

Step 1: Secure the band (800 or 1800) and modulation
type, or more importantly, *the air-interface type*
that the system is using on the phone you desire access
to.

Step 2: Radiate an RF signal on the "best known server"
in the area that belongs to the system the phone
has been programmed for - modulate this RF signal
with the system parameters set for auto-registration
using the smallest time value (time interal) for
auto-regs that is possible.

Step 3: DF on the registration attepmts that occur.

(Effectively you have erected your own microcell
with your own control channel parameters.)

The downside is - every other phone that happens
across that simulated, local control channel is
going to attepmt to register as well ...



**** Your better bet is to monitor for all periodic
registration attempts on all systems in that area - some
of those registrations will be workers - perhaps one
(or more) will be from victims buried in rubble ...


  "Otherwise, you're stuck with numbing the receiver
   till all it can pick up"

A wideband noise source on all but one (perhaps locally
generated?) control channel which will force the phone
to seek it out above all others?

... still requires the correct control channel signal
containing all the correct info (sysid's etc) otherwise
the phone is likely to reject it and keep looking for
the 'home' system (highly dependent on phone programming
and air-interface spec at this point).

Jim



{Original Message removed}

2001\09\14@195355 by Peter L. Peres

picon face
Jim:

- the price of the antenna you think of may be FOB where you are. I was
talking about FOB here.

- the antenna I saw did have a dipole array inside but the cover was far
too thick to be just a cover, so I think that it was a lens.

- two ~30dB gain Yagis were required in a downlink from OSCAR?? satellites
on 432MHz. I do not remember the details. The Yagis had umpteen elements
(24 or more) each. They were built by hand using Al tubing and Al profile
for the girder according to plans from a magazine or book. This was a
friend's project so I do not know all the details. I assume that they
could be used in the opposite direction by feeding them with the
sattelite's tx power downgraded by the antenna gain, which should put it
about at the 0.6W level for an OSCAR sattelite but I am not sure about
their transponder powers.

- the bandwidth required to pass digital data by a cellular phone (GSM)
channel is about three times the bandwidth of a SSB voice channel and
requires a better S/N ratio than SSB for correct operation. With adjacent
channel etc it is probably even wider. Thus the equivalent power/bandwidth
is much lower. We are talking earth to space since the space segment is
supposed to determine the cellphone position.

- there are no 10 mile cells anywhere that I know of. There has to be a
reason for this.

- afaik EPIRBs have two frequencies, one is 130MHz-ish and the other
450MHz-ish. I need to look them up to be sure. They also have very narrow
band transmissions and were specifically designed for uplinks in difficult
conditions.

Peter

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2001\09\17@014816 by dr. Imre Bartfai

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Hello,

I have an maybe interesting idea at this topic:

a national authority could order all cell phones should be attached with a
GPS receivers and on a request of the central tower they sould give their
positions immediately. The whole thing could be transparent to the user
such way it can be even hidden. Who knows whether it has been done
already? ;-)
I am not paranoid. But Andy Grove has written the book with title: Only
Paranoids survive.

Regards,
Imre

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On Thu, 13 Sep 2001, Chris Carr wrote:

{Quote hidden}

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2001\09\17@020438 by brady

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You'd better have a clear view of the sky at all times.

-----Original Message-----
From: pic microcontroller discussion list
[RemoveMEPICLISTspamspamBeGoneMITVMA.MIT.EDU]On Behalf Of dr. Imre Bartfai
Sent: Friday, September 14, 2001 5:49 AM
To: spamBeGonePICLIST@spam@spamspam_OUTMITVMA.MIT.EDU
Subject: Re: [OT]:cell phone locating


Hello,

I have an maybe interesting idea at this topic:

a national authority could order all cell phones should be attached with a
GPS receivers and on a request of the central tower they sould give their
positions immediately. The whole thing could be transparent to the user
such way it can be even hidden. Who knows whether it has been done
already? ;-)
I am not paranoid. But Andy Grove has written the book with title: Only
Paranoids survive.

Regards,
Imre

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| to which it is addressed and may contain confidential and/or          |
| privileged material.  Any review, retransmission, dissemination or    |
| other use of, or taking of any action in reliance upon, this          |
| information by persons or entities other than the intended recipient  |
| is prohibited. If you received this in error, please contact the      |
| sender and delete the material from any computer.                     |
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On Thu, 13 Sep 2001, Chris Carr wrote:

{Quote hidden}

However,
> my first comment was genuine.
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2001\09\17@022540 by David VanHorn

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>
>a national authority could order all cell phones should be attached with a
>GPS receivers and on a request of the central tower they sould give their
>positions immediately. The whole thing could be transparent to the user
>such way it can be even hidden. Who knows whether it has been done
>already? ;-)
>I am not paranoid. But Andy Grove has written the book with title: Only
>Paranoids survive.

You're aware that GPS receivers need a clear view of the sky, right?
They don't work even in a wooden house.
Under a car roof is shaky.

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2001\09\17@094902 by Jim

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   "You're aware that GPS receivers need
    a clear view of the sky, right?

    They don't work even in a wooden
    house."

Hmmm  - I've had (and continue to have) good
results with GPS in my wooden roof/brick
facade home ...

Also, you might want to look into what
http://www.snaptrack.com is able to achieve as far
as results within structures, and then there
is also the operational scenario where THE
PHONE/GPS combo *remembers* the last known
good fix GPS position fix ...

Jim

{Original Message removed}

2001\09\17@105053 by Russell McMahon

picon face
Results can be quite variable.

Located on a window sill with metal frames but a clear line of site to the
satellite reception is inconsistent.
Under tree foliage can be enough to prevent reception.
I have a concrete tile roofed house with no substantial metal in it but get
no coverage indoors.



     Russell McMahon
_____________________________


>     "You're aware that GPS receivers need
>      a clear view of the sky, right?
>
>      They don't work even in a wooden
>      house."
>
> Hmmm  - I've had (and continue to have) good
> results with GPS in my wooden roof/brick
> facade home ...

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2001\09\17@112636 by Dan Larson

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On Fri, 14 Sep 2001 11:48:56 +0200, dr. Imre Bartfai wrote:

>Hello,
>
>I have an maybe interesting idea at this topic:
>
>a national authority could order all cell phones should be attached with a
>GPS receivers and on a request of the central tower they sould give their
>positions immediately. The whole thing could be transparent to the user
>such way it can be even hidden. Who knows whether it has been done
>already? ;-)
>I am not paranoid. But Andy Grove has written the book with title: Only
>Paranoids survive.

You could always turn off your phone! <G>

If they were using the damned things to track people,
I sure wouldn't want to carry one in the first place!

I bet most people feel the same way. The cell phone
industry would suffer badly when everyone starts to
throw their phones away.

Just a thought...

Dan

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2001\09\17@112656 by Jim

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  Russell McMahon:
     "concrete tile roofed"

From my experience with propagation at 800 MHz
(cellular system engineering) concrete is *not*
transparent to RF ...

My GPS results encompass both an early Magellan
unit (circa '94) and OEM modules. The Magellan is
by far 'pickier' about where it's situated/sitting.

I'm curious - you've got a concrete tiled roof - what
about the exterior walls - trowelled cement over a
metal screen by any chance (the name of this style of
construction presently escapes me)? *These* are also
big signal killers.

You may be living in a low-grade 'screen room', Russell ...

Jim


{Original Message removed}

2001\09\19@034304 by Peter L. Peres

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>GPS

Did you know that a simple thatched roof with wooden beams and almost no
metal in it stops GPS signals ?

Peter

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