Cingular cell phone service - Re: 911 Call location accuracy

Author

Re: 911 Call location accuracy

Evan Platt

2007-04-30, 3:33 pm

On Sun, 29 Apr 2007 15:21:50 GMT, John Navas
< spamfilter1@navasgro
up.com> wrote:

>
>AT&T/Cingular E911 positioning is actually done by U-TDOA. I suggest
>you read up on it in order to avoid making more inaccurate statements.
>See links in the Cingular FAQ below.

Triangulation doesn't require 3 or more points? (In general).

>
>The A-GPS (Assisted GPS) used in cell phones isn't that accurate, and
>doesn't work at all in many locations, including many urban areas, under
>tree cover, indoors, etc. Again, you clearly need to read up on the
>technology in order to avoid making inaccurate statements.

Where did I say A-GPS?
--
To reply via e-mail, remove The Obvious from my e-mail address.

Dennis Ferguson

2007-04-30, 3:33 pm

On 2007-04-30, Evan Platt <evan@theobvious.espphotography.com> wrote:
> On Sun, 29 Apr 2007 15:21:50 GMT, John Navas
>< spamfilter1@navasgro
up.com> wrote:
>
>
> Triangulation doesn't require 3 or more points? (In general).

Actually, to be anally correct, triangulation requires direction measurements
from two points whose (longitude, latitude) location is known to determine
the (longitude, latitude) location of a third point. If it were operating
by triangulation two (known location) towers would do it for finding
one (unknown location) phone, I guess.

The difference is that the Cingular system isn't doing triangulation, it
is a hyperbolic navigation system (like GPS and Loran C). For this
you have to solve for three unknowns (longitude, latitude, time) which
requires three measurements from three towers at three known locations.

FWIW, the SnapTrack system can get positioning with no GPS and just two
towers since it measures an extra bit of information, the round trip time
from the phone to the base station it is currently homed to (this is
equivalent to determining the `time' unknown separately). It can do this
because the phone is cooperating in the measurement; I don't think the
Cingular system can do this (?) because it has to work with unmodified,
uncooperative phones.

Dennis Ferguson

John Navas

2007-04-30, 10:33 pm

On Mon, 30 Apr 2007 11:26:40 -0700, Evan Platt
<evan@theobvious.espphotography.com> wrote in
< j5dc33h92t3nuhmibu71
bqgnc22k0545n0@4ax.com>:

>On Sun, 29 Apr 2007 15:21:50 GMT, John Navas
>< spamfilter1@navasgro
up.com> wrote:
>
>
>Triangulation doesn't require 3 or more points? (In general).

U-TDOA isn't just a simple triangulation system, as CDMA proponents try
to suggest:

U-TDOA technology works very well in urban, suburban and indoor
environments -- suffering only in extreme rural conditions where the
cell sites are arranged in a "string of pearls" configuration. In
such scenarios, TruePosition can supplement its U-TDOA technology
with Angle of Arrival (AOA) technology, which computes locations
based on the angle at which signal reached two base stations.

>
>Where did I say A-GPS?

Cell phones generally use A-GPS.

--
Best regards, FAQ FOR CINGULAR WIRELESS:
John Navas <http://en.wikibooks.org/wiki/ Cingu...less_FA
Q>

Scott

2007-04-30, 10:33 pm

John Navas < spamfilter1@navasgro
up.com> wrote in
news:mtkc331k2ejb1vf
cek4gsgj1s4fmpa5stf@
4ax.com:

> On Mon, 30 Apr 2007 11:26:40 -0700, Evan Platt
> <evan@theobvious.espphotography.com> wrote in
> < j5dc33h92t3nuhmibu71
bqgnc22k0545n0@4ax.com>:
>
>
> U-TDOA isn't just a simple triangulation system, as CDMA proponents try
> to suggest:
>
> U-TDOA technology works very well in urban, suburban and indoor
> environments -- suffering only in extreme rural conditions where the
> cell sites are arranged in a "string of pearls" configuration. In
> such scenarios, TruePosition can supplement its U-TDOA technology
> with Angle of Arrival (AOA) technology, which computes locations
> based on the angle at which signal reached two base stations.
>

And if the user is located between the towers...

LinkBot