911 Call location accuracy

On 2007-04-29, John Navas <[email protected]> wrote:
> On Sat, 28 Apr 2007 13:24:22 -0700, Evan Platt
><[email protected]> wrote in
><[email protected]>:
>
>>On Sat, 28 Apr 2007 11:13:22 -0700, "al" <[email protected]>
>>wrote:
>>
>>>I read an article concerning the accurancy in determining a 911 caller's
>>>location. Two systems were compared, a "network based" system (ATT
>>>Cingular) and a "satellite GPS" system (Verizon Sprint).
>>>It seems that the satellite GPS system could pinpoint the caller more
>>>frequently than the network system. If I understand the ATT system, the
>>>call must be picked up by 2 or 3 cell phone towers and the location is then
>>>calculated by trianguation. Chances of contacting 2 or 3 towers in some
>>>areas is remote. The Satellite GPS system may be hindered in some
>>>metropolitan areas because it is harder to see sufficient GPS satellites.
>>
>>Yep, that about sums it up.
>
> Actually not.
>
>>Triangulation requires at least 3. The more, the merrier.
>
> 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.

So are you saying you can do TDOA positioning with fewer than three
tower measurements? How?

I know it can fall back to direction-and-signal-strength ranging when
it has less than 3 towers to work with, but these measurements are crap.

>>And satellite, if GPS, is accurate to I believe 3 meters.
>
> 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.

Have you seen any A-GPS in use in cell phones other than Qualcomm's?
The SnapTrack Wireless Assisted GPS(TM) is actually a hybrid which takes
TOA measurements from both available GPS satellites and from all the
towers it can hear, and reports all these to the network. In the case
where it can't hear any GPS satellites it continues to work but makes
do with tower-based data alone like the Cingular system (I hope you aren't
defining "working like Cingular" as "not working"). If it can also
measure GPS satellite TOAs it works even better.

Dennis Ferguson

---

› See More: 911 Call location accuracy

Dennis Ferguson wrote:

> Have you seen any A-GPS in use in cell phones other than Qualcomm's?
> The SnapTrack Wireless Assisted GPS(TM) is actually a hybrid which takes
> TOA measurements from both available GPS satellites and from all the
> towers it can hear, and reports all these to the network. In the case
> where it can't hear any GPS satellites it continues to work but makes
> do with tower-based data alone like the Cingular system (I hope you aren't
> defining "working like Cingular" as "not working"). If it can also
> measure GPS satellite TOAs it works even better.
>
> Dennis Ferguson

Yes, Verizon is using Snaptrack and the accuracy is very very good, and
the hybrid design ensures that it works indoors as well. I only know one
company that's using location based services, but it's very large, and
they chose Verizon based mainly on their need for accurate positioning.
They've been getting accuracy to about 15 meters. The TDOA system used
by Cingular has much poorer accuracy. Cingular has promised that they
will be implementing a more accurate system in the future, not later
than the end of 2008.

Companies that need to implement location based services are flocking to
the CDMA carriers because the GSM carriers (at least in the U.S.) have
not yet implemented Snaptrack (or similar systems).



[Copied to alt.cellular.attws. Please post all alt.cellular.cingular
posts to alt.cellular.attws as well. The Cingular name is going away,
and alt.cellular.attws is the proper venue for posts regarding AT&T's
Wireless Service.]

On Sun, 29 Apr 2007 18:42:00 -0500, Dennis Ferguson
<[email protected]> wrote in
<[email protected]>:

>On 2007-04-29, John Navas <[email protected]> wrote:
>> On Sat, 28 Apr 2007 13:24:22 -0700, Evan Platt

>> 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.
>
>So are you saying you can do TDOA positioning with fewer than three
>tower measurements?

Yes.

>How?

As I wrote, read up on it. Also on sector antennas. Likewise position
mapping.

>I know it can fall back to direction-and-signal-strength ranging when
>it has less than 3 towers to work with, but these measurements are crap.

You would be misinformed.

>>>And satellite, if GPS, is accurate to I believe 3 meters.
>>
>> 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.
>
>Have you seen any A-GPS in use in cell phones other than Qualcomm's?

Yes.

>The SnapTrack Wireless Assisted GPS(TM) is actually a hybrid which takes
>TOA measurements from both available GPS satellites and from all the
>towers it can hear, and reports all these to the network. In the case
>where it can't hear any GPS satellites it continues to work but makes
>do with tower-based data alone like the Cingular system (I hope you aren't
>defining "working like Cingular" as "not working"). If it can also
>measure GPS satellite TOAs it works even better.

Read world results are considerably less accurate and reliable than you7
suggest.

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

On Sun, 29 Apr 2007 17:15:23 -0700, SMS <[email protected]>
wrote in <[email protected]>:

>Companies that need to implement location based services are flocking to
>the CDMA carriers because the GSM carriers (at least in the U.S.) have
>not yet implemented Snaptrack (or similar systems).

Proof? Or another of your fantasies?

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

On 2007-04-30, John Navas <[email protected]> wrote:
> On Sun, 29 Apr 2007 18:42:00 -0500, Dennis Ferguson wrote:
>>I know it can fall back to direction-and-signal-strength ranging when
>>it has less than 3 towers to work with, but these measurements are crap.
>
> As I wrote, read up on it. Also on sector antennas. Likewise position
> mapping.

Exactly. Like I said, crap. Of course A-GPS systems can do this too,
and the measurements are just as crappy. They just don't need to do
it as often.

>>>>And satellite, if GPS, is accurate to I believe 3 meters.
>>>
>>> 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.
>>
>>Have you seen any A-GPS in use in cell phones other than Qualcomm's?
>
> Yes.

So which A-GPS have you seen which doesn't work indoors?

>>The SnapTrack Wireless Assisted GPS(TM) is actually a hybrid which takes
>>TOA measurements from both available GPS satellites and from all the
>>towers it can hear, and reports all these to the network. In the case
>>where it can't hear any GPS satellites it continues to work but makes
>>do with tower-based data alone like the Cingular system (I hope you aren't
>>defining "working like Cingular" as "not working"). If it can also
>>measure GPS satellite TOAs it works even better.
>
> Read world results are considerably less accurate and reliable than you7
> suggest.

Hey, what happened to your assertion that A-GPS systems didn't work indoors,
i.e.

> 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.

? I'd like to read up on that.

I didn't suggest any level of accuracy and reliability other than it
is at least as good as U-TDOA. Good luck proving otherwise.

Dennis Ferguson

Dennis Ferguson wrote:

> I didn't suggest any level of accuracy and reliability other than it
> is at least as good as U-TDOA. Good luck proving otherwise.

Someone had better tell the sales people trying to sell LBS systems
based on U-TDOA about Navas's claims. The big selling point of the
Snaptrack based LBS systems is the much higher accuracy, while the
U_TDOA systems are being sold solely on lower cost.

You also have all those European carriers needlessly implementing hybrid
systems because they foolishly failed to consult with the self-appointed
expert on everything. They could have saved a lot of money if only
someone had told them that U-TDOA could provide sufficiently accurate
positioning for their LBS applications, without the need for more
expensive handsets, and without the need for all the infrastructure.

I can think of one big advantage of the U-TDOA LBS systems, they'd cause
less union opposition due to their lower accuracy. The union workers
that are being tracked with the Snaptrack system are not happy about it.


[Copied to alt.cellular.attws. Please post all alt.cellular.cingular
posts to alt.cellular.attws as well. The Cingular name is going away,
and alt.cellular.attws is the proper venue for posts regarding AT&T's
Wireless Service.]

On Mon, 30 Apr 2007 16:07:19 -0500, Dennis Ferguson
<[email protected]> wrote in
<[email protected]>:

>On 2007-04-30, John Navas <[email protected]> wrote:

>> As I wrote, read up on it. Also on sector antennas. Likewise position
>> mapping.
>
>Exactly. Like I said, crap.

In fact the position accuracy of TruePosition U-TDOA (as used by
AT&T/Cingular) with two receivers and reception angle is good, on par
with accuracy with three receivers (where angle data isn't needed).
Angle data is what makes the difference.

>Of course A-GPS systems can do this too,
>and the measurements are just as crappy. They just don't need to do
>it as often.

A-GPS depends on reception of GPS signals by the handset, which is a
problem in many locations (urban canyons, under tree cover, indoors,
etc.). Because of this serious weakness, hybrid A-GPS systems (e.g.,
SnapTrack) augment GPS, using Enhanced Cell-ID with CDMA200 that's
relatively crude as compared to U-TDOA with GSM.

>So which A-GPS have you seen which doesn't work indoors?

All of them. A-GPS requires GPS signals to work. Without such signals,
accuracy depends on how much the handset has moved since the last
position fix and on what other location data is available.

>I didn't suggest any level of accuracy and reliability other than it
>is at least as good as U-TDOA. Good luck proving otherwise.

Enhanced Cell-ID has an accuracy of only 75-500 meters, far less
accurate than U-TDOA as used in TruePosition U-TDOA.

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

On Mon, 30 Apr 2007 14:34:04 -0700, SMS <[email protected]>
wrote in <[email protected]>:

>Dennis Ferguson wrote:
>
>> I didn't suggest any level of accuracy and reliability other than it
>> is at least as good as U-TDOA. Good luck proving otherwise.
>
>Someone had better tell the sales people trying to sell LBS systems
>based on U-TDOA about Navas's claims. The big selling point of the
>Snaptrack based LBS systems is the much higher accuracy, while the
>U_TDOA systems are being sold solely on lower cost.

SnapTrack is actually quite a bit less accurate than U-TDOA when a GPS
fix isn't available (as is often the case; e.g., in urban canyons, under
tree cover, indoors, etc.) because it relies on relatively crude
Enhanced Cell-ID.

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

On 2007-04-30, John Navas <[email protected]> wrote:
> On Mon, 30 Apr 2007 14:34:04 -0700, SMS <[email protected]>
> wrote in <[email protected]>:
>
>>Dennis Ferguson wrote:
>>
>>> I didn't suggest any level of accuracy and reliability other than it
>>> is at least as good as U-TDOA. Good luck proving otherwise.
>>
>>Someone had better tell the sales people trying to sell LBS systems
>>based on U-TDOA about Navas's claims. The big selling point of the
>>Snaptrack based LBS systems is the much higher accuracy, while the
>>U_TDOA systems are being sold solely on lower cost.
>
> SnapTrack is actually quite a bit less accurate than U-TDOA when a GPS
> fix isn't available (as is often the case; e.g., in urban canyons, under
> tree cover, indoors, etc.) because it relies on relatively crude
> Enhanced Cell-ID.

For GSM networks with unmodified base station transmitters, maybe.
For (W)CDMA networks, where transmissions are time-synchronous (and
for GSM networks which have been made so), it uses Time of Arrival
measurements exactly like U-TDOA.

Dennis Ferguson

Dennis Ferguson wrote:

> For GSM networks with unmodified base station transmitters, maybe.
> For (W)CDMA networks, where transmissions are time-synchronous (and
> for GSM networks which have been made so), it uses Time of Arrival
> measurements exactly like U-TDOA.

This is correct.

More importantly, the big users of LBS systems are companies tracking
the location of field personnel, delivery trucks, etc., so there is no
issue with getting a satellite fix to enhance accuracy. At least in the
U.S. the LBS users did extensive field testing of the different
technologies, and the hybrid systems proved to be much more accurate.
For some applications, the lower accuracy of U-TDOA is acceptable, for
some it is not. This is the reason that the GSM carriers are deploying
hybrid systems.

On Mon, 30 Apr 2007 17:14:25 -0500, Dennis Ferguson
<[email protected]> wrote in
<[email protected]>:

>On 2007-04-30, John Navas <[email protected]> wrote:
>> On Mon, 30 Apr 2007 14:34:04 -0700, SMS <[email protected]>
>> wrote in <[email protected]>:
>>
>>>Dennis Ferguson wrote:
>>>
>>>> I didn't suggest any level of accuracy and reliability other than it
>>>> is at least as good as U-TDOA. Good luck proving otherwise.
>>>
>>>Someone had better tell the sales people trying to sell LBS systems
>>>based on U-TDOA about Navas's claims. The big selling point of the
>>>Snaptrack based LBS systems is the much higher accuracy, while the
>>>U_TDOA systems are being sold solely on lower cost.
>>
>> SnapTrack is actually quite a bit less accurate than U-TDOA when a GPS
>> fix isn't available (as is often the case; e.g., in urban canyons, under
>> tree cover, indoors, etc.) because it relies on relatively crude
>> Enhanced Cell-ID.
>
>For GSM networks with unmodified base station transmitters, maybe.
>For (W)CDMA networks, where transmissions are time-synchronous (and
>for GSM networks which have been made so), it uses Time of Arrival
>measurements exactly like U-TDOA.

Proof? SnapTrack states "Enhanced Cell ID".

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

On Mon, 30 Apr 2007 15:31:12 -0700, SMS <[email protected]>
wrote in <[email protected]>:

>Dennis Ferguson wrote:
>
>> For GSM networks with unmodified base station transmitters, maybe.
>> For (W)CDMA networks, where transmissions are time-synchronous (and
>> for GSM networks which have been made so), it uses Time of Arrival
>> measurements exactly like U-TDOA.
>
>This is correct.
>
>More importantly, the big users of LBS systems are companies tracking
>the location of field personnel, delivery trucks, etc., so there is no
>issue with getting a satellite fix to enhance accuracy. At least in the
>U.S. the LBS users did extensive field testing of the different
>technologies, and the hybrid systems proved to be much more accurate.
>For some applications, the lower accuracy of U-TDOA is acceptable, for
>some it is not. This is the reason that the GSM carriers are deploying
>hybrid systems.

Proof? Or yet another made up claim?

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

On 2007-04-30, John Navas <[email protected]> wrote:
> On Mon, 30 Apr 2007 17:14:25 -0500, Dennis Ferguson wrote:
>>> SnapTrack is actually quite a bit less accurate than U-TDOA when a GPS
>>> fix isn't available (as is often the case; e.g., in urban canyons, under
>>> tree cover, indoors, etc.) because it relies on relatively crude
>>> Enhanced Cell-ID.
>>
>>For GSM networks with unmodified base station transmitters, maybe.
>>For (W)CDMA networks, where transmissions are time-synchronous (and
>>for GSM networks which have been made so), it uses Time of Arrival
>>measurements exactly like U-TDOA.
>
> Proof? SnapTrack states "Enhanced Cell ID".

I have other reasons to be familiar with how this works, however
these will do:

http://www.snaptrack.com/pdf/ion2002...ermination.pdf
http://www.snaptrack.com/pdf/ion2002...ybrid_agps.pdf

I do notice we've moved well beyond "doesn't work indoors". Keep
reading and you'll get up to speed.

Dennis Ferguson

On Mon, 30 Apr 2007 18:18:23 -0500, Dennis Ferguson
<[email protected]> wrote in
<[email protected]>:

>On 2007-04-30, John Navas <[email protected]> wrote:
>> On Mon, 30 Apr 2007 17:14:25 -0500, Dennis Ferguson wrote:
>>>> SnapTrack is actually quite a bit less accurate than U-TDOA when a GPS
>>>> fix isn't available (as is often the case; e.g., in urban canyons, under
>>>> tree cover, indoors, etc.) because it relies on relatively crude
>>>> Enhanced Cell-ID.
>>>
>>>For GSM networks with unmodified base station transmitters, maybe.
>>>For (W)CDMA networks, where transmissions are time-synchronous (and
>>>for GSM networks which have been made so), it uses Time of Arrival
>>>measurements exactly like U-TDOA.
>>
>> Proof? SnapTrack states "Enhanced Cell ID".
>
>I have other reasons to be familiar with how this works, however
>these will do:
>
> http://www.snaptrack.com/pdf/ion2002...ermination.pdf
> http://www.snaptrack.com/pdf/ion2002...ybrid_agps.pdf

What matters, of course, is what's actually in the field, and how well
it performs in the real world.

<http://www.snaptrack.com/technology/index.jsp>
<http://www.cdmatech.com/docs_details/tech_demos/demos/gpsone_hybrid.html>

Wireless Network

Base stations in the wireless network not only
provide communications coverage, but may
deliver adjunct locations information, such as
Enhanced Cell-ID that aids the location
process and ensures all-terrain availability of
location information.

<http://www.iec.org/online/tutorials/tcs/topic01.html>

Enhanced Cell-ID - Enhanced Cell-ID is a network technology that
combines Cell ID (CI) with one or more additional technologies. The
level of accuracy is increased over basic Cell ID, ranging from 75 -
500 meters. In GSM networks, CI can be combined with Timing Advance
(which measures handset range from the base station, including
whether or not the handset is connected to the nearest cell) and/or
Received Signal Level (which measures average signal strength). In
W-CDMA networks, CI can be combined with Round-Trip-Time (W-CDMA
version of Timing Advance) to improve accuracy.

>I do notice we've moved well beyond "doesn't work indoors".

On the contrary -- A-GPS simply doesn't work without GPS signals (e.g.,
in urban canyons, under tree cover, _indoors_) -- kindly refrain from
trying to put words in my mouth.

Hybrid A-GPS systems are a result of scrambling to overcome the serious
limitations of A-GPS-based positioning alone, which doesn't work well or
at all in many environments.

>Keep
>reading and you'll get up to speed.

Ditto.

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

On 2007-04-30, John Navas <[email protected]> wrote:
> On Mon, 30 Apr 2007 16:07:19 -0500, Dennis Ferguson
><[email protected]> wrote in
><[email protected]>:
>
>>On 2007-04-30, John Navas <[email protected]> wrote:
>
>>> As I wrote, read up on it. Also on sector antennas. Likewise position
>>> mapping.
>>
>>Exactly. Like I said, crap.
>
> In fact the position accuracy of TruePosition U-TDOA (as used by
> AT&T/Cingular) with two receivers and reception angle is good, on par
> with accuracy with three receivers (where angle data isn't needed).
> Angle data is what makes the difference.

If you say so. Hybrid A-GPS doesn't need the angle to handle the
two tower case (it can be done just with timing information), only
the one tower case.

>>Of course A-GPS systems can do this too,
>>and the measurements are just as crappy. They just don't need to do
>>it as often.
>
> A-GPS depends on reception of GPS signals by the handset, which is a
> problem in many locations (urban canyons, under tree cover, indoors,
> etc.). Because of this serious weakness, hybrid A-GPS systems (e.g.,
> SnapTrack) augment GPS, using Enhanced Cell-ID with CDMA200 that's
> relatively crude as compared to U-TDOA with GSM.

This would imply you've seen non-hybrid A-GPS implemented on some
cell phone (since that's what you said). Which one?

It's also wrong. In a CDMA network GPSone does TOA measurements
on the towers just like U-TDOA. The accuracy is 1/16 of a CDMA chip, or
about 15m for CDMA2000, though the vagarity of terrestrial RF paths
degrades this (just like U-TDOA).

>>So which A-GPS have you seen which doesn't work indoors?
>
> All of them. A-GPS requires GPS signals to work. Without such signals,
> accuracy depends on how much the handset has moved since the last
> position fix and on what other location data is available.

This would imply you've seen non-hybrid A-GPS implemented on some
cell phone (since that's what you said). Which one?

>>I didn't suggest any level of accuracy and reliability other than it
>>is at least as good as U-TDOA. Good luck proving otherwise.
>
> Enhanced Cell-ID has an accuracy of only 75-500 meters, far less
> accurate than U-TDOA as used in TruePosition U-TDOA.

Proof?

Again, in networks with time-synchronous transmitters (which includes
all flavours of CDMA, and could include non-standard GSM made to do
so) TOA measurements are used, just like U-TDOA.

Dennis Ferguson