911 Call location accuracy

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al - 28 Apr 2007 19:13 GMT

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.
The article can be seen at http://www.msnbc.msn.com/id/18294965/

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Evan Platt - 28 Apr 2007 21:24 GMT

>I read an article concerning the accurancy in determining a 911 caller's
>location. Two systems were compared, a "network based" system (ATT
[quoted text clipped - 5 lines]
>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.

Triangulation requires at least 3. The more, the merrier.

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

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John Navas - 29 Apr 2007 16:21 GMT

>>I read an article concerning the accurancy in determining a 911 caller's
>>location. Two systems were compared, a "network based" system (ATT
[quoted text clipped - 7 lines]
>
>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.

>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.

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

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SMS - 29 Apr 2007 04:12 GMT

> I read an article concerning the accurancy in determining a 911 caller's
> location. Two systems were compared, a "network based" system (ATT
[quoted text clipped - 4 lines]
> calculated by trianguation. Chances of contacting 2 or 3 towers in some
> areas is remote.

The problem is that even with 3 towers, the network based system isn't
accurate to a sufficient level for many location-based services.

See "http://eetimes.eu/wireless/showArticle.jhtml?articleID=193200680"

"ABI said it sees 2007 as the year the GSM carriers will issue requests
for qualifications and vendor selection and IC integration for the
handset OEMs will take place. By the end of 2008, a quarter of all 3G
handsets will have GPS ICs included, and the average selling price of a
GPS chipset will have dropped to $2.70, ABI said."

As usual, GSM lags CDMA by a few years.

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Todd Allcock - 29 Apr 2007 07:09 GMT

> The problem is that even with 3 towers, the network based system isn't
> accurate to a sufficient level for many location-based services.

So? The E911 "location" mandate was for safety- not delivery-truck
tracking. It's
accurate enough for it's intended purpose.

> See "http://eetimes.eu/wireless/showArticle.jhtml?articleID=193200680"
>
[quoted text clipped - 5 lines]
>
> As usual, GSM lags CDMA by a few years.

That's quite unfair. First, the advantage of tower locatation-based
positioning is that works with any phone registered on the network. I
can be tracked when dialing 911 on my six year-old Nokia 8290 just as
easily and as accurately as I can on my current PPC phone. GSM customers
never have to hear "I'm sorry- we can't let you use your perfectly good
old phone on our network because it isn't E911 compatible."

Plus, nothing has prevented integration of GPS chips in GSM phones.
Unlike with CDMA, GSM has let the marketplace decide if higher-accuracy
GPS was desired by customers, AND because of this, the carrier doesn't
have to be involved in the services- 3rd party companies can develop
tracking software because the GPS chips in GSM handsets "belong" to the
phone's owner- not the carrier! Can you pull your location out of your
GPS-enabled CDMA phone? No, but Verizon can, and then sell your phone's
own data back to you!

An HP 6515 owner, for example, can pull up his or her lat/long by
him/herself, and any number of 3rd-party Windows Mobile applications can
be written to read that info from the GPS and text it or upload it to
whoever without paying Cingular anything except the cost of the data
transfer.

Verizon or Sprint, on the other hand, wouldn't dare allow a "real" user
accessible GPS module to be built into a phone- that $10/month nav
software or $30/month tracking software subscription would be threatened.

GSM is certainly a few years "behind" CDMA in some aspects- like finding
new ways to milk a customer's wallet on a monthly basis for hardware
already built into the phone. Unfortunately, with the increased handset
crippling we're beginning to see from GSM carriers as well, it seems
they're trying to catch up, sadly.

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John Navas - 29 Apr 2007 16:15 GMT

>> As usual, GSM lags CDMA by a few years.
>
>That's quite unfair.

It's also dead wrong, like the rest of his anti-GSM mantra, endlessly
trolled in GSM newsgroups. He's obviously got way too much free time.
;)

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

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SMS - 30 Apr 2007 20:08 GMT

> Plus, nothing has prevented integration of GPS chips in GSM phones.

You're comparing apples and oranges.

The advantage of the Snaptrack system is that it's a hybrid system for
locating the phone.

The GPS applications you can run on a PDA phone are unrelated to LBS or
E-911. It's true that some of the GPS chip-equipped CDMA phones can run
other GPS applications, but there are also GSM phones with that capability.

It's in LBS services that require a high-degree of accuracy that the
CDMA carriers have an advantage. Personally I'm of the opinion that it's
really unethical to watch every move your employees make, but others
argue that since you're paying them, you have the right to track their
every move. Obviously the users of LBS and the service providers have
the latter opinion.

You'll get no argument from me that it sucks that you can't use you're
older phones on CDMA networks. Actually you can use them on some MVNO
networks, such as PagePlus. I also despise what companies like Verizon
do by defeaturing handsets to turn off functionality that the
manufacturer included. There are no saints here.

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John Navas - 30 Apr 2007 22:14 GMT

>> Plus, nothing has prevented integration of GPS chips in GSM phones.
>
>You're comparing apples and oranges.

That's what you're doing.

>The advantage of the Snaptrack system is that it's a hybrid system for
>locating the phone.

The advantage of U-TDOA is that it's a system that works with _any_
phone.

>It's in LBS services that require a high-degree of accuracy that the
>CDMA carriers have an advantage. ...

There isn't actually a meaningful difference in LBS.

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

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Todd Allcock - 01 May 2007 06:45 GMT

> You're comparing apples and oranges.

True- to a point. I was jumping on your comment that GSM was a "few
years behind CDMA." The two major US GSM carriers chose the less
accurate system for sound business reasons, not because of any
technological reason preventing a more accurate assisted-GPS system. IIRC,

the Feds required 95% of the handsets on the system to be E-911 compliant
by a certain date, and unless the GSM guys wanted to start excersizing
the same draconian control of handsets on their networks that Sprint and
Verizon do, the system they chose made sense.

> The advantage of the Snaptrack system is that it's a hybrid system for
> locating the phone.

I understand that. Verizon, Sprint and their resellers (like Disney
Mobile) are leveraging the more accurate system for addition revenue.
There's nothing wrong with that, (except every customer is paying for
those AGPS Qualcomm chips regardless of the fact that probably only 1% of
the customer base want or need L-B services.) My point was only that GSM
carriers could (and have) offered GPS capable handsets, so they could
choose to offer LBS (with the caviat that you'd be required to use
particular handsets instead of any handset, like with CDMA.)

> The GPS applications you can run on a PDA phone are unrelated to LBS
> or E-911.

You're missing my point- noth ing PREVENTS the GPS systems in those
phones from being used for LBS- look at Wherify, for example- they're a
Cingular reseller that puts a "real" GPS chip in a GSM "kiddle phone" so
parents can track location (sort of a prepaid version of Disney Mobile's
tracking service.) It's an overpriced service, IMHO, but it's an example
of how a 3rd-party can leverage LBS over cellular instead of only the
carrier.

> It's true that some of the GPS chip-equipped CDMA phones can run other
> GPS applications, but there are also GSM phones with that capability.

Again, building in a "real" non-carrier assisted GPS (like the Nokia N95)
allows for third parties to develop LBS apps and bypass or undercut the
carrier's (so far) virtual monopoly on LBS. I wouldn't be surprised to
see 3rd-party LBS software written for N95s shortly. You wouldn't even
need a monthly subscription to a carrier-based service if a 3rd-party
sold software for the N95 that reported position via SMS or GPRS every x
minutes and a desktop/server app processing that data at the employer's
location. The 3rd party opportunities are endless with an "open" system
like Nokia's and impossible with a closed system like Qualcomm's.

> It's in LBS services that require a high-degree of accuracy that the
> CDMA carriers have an advantage.

Agreed. My point was that if there was (or is) a large market for LBS,
phone manufactures would've exploited it outside of the carrier's system
(vehicle-mounted LBS units already exist that record data internally for
upload to a PC back at "base" or transmit via cellular- this is, obviously,

a niche market that GPS-enabled phones now compete with.)

> Personally I'm of the opinion that it's really unethical to watch every
> move your employees make, but others argue that since you're paying
> them, you have the right to track their every move. Obviously the
> users of LBS and the service providers have the latter opinion.

I agree with you completely, but like with drug-testing, it's another
place the market can decide- if you don't want to be tracked, (or tested)
get a job with an employer that doesn't track or test.

> You'll get no argument from me that it sucks that you can't use you're
> older phones on CDMA networks. Actually you can use them on some MVNO
> networks, such as PagePlus.

Yes- since they represent an infinitesmal number of customers compared to
Verizon's retail biz, they exist in the 5% of customers the Feds allow
Verizon to have using non-E911 handsets.

>I also despise what companies like Verizon do by defeaturing handsets
> to turn off functionality that the manufacturer included. There are no
> saints here.

Agreed. That is certainly an area where GSM IS "years behind CDMA."
;-)

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xPosTech - 02 May 2007 10:57 GMT

> the Feds required 95% of the handsets on the system to be E-911 compliant
> by a certain date, and unless the GSM guys wanted to start *excersizing*
> the same draconian control of handsets on their networks that Sprint and
> Verizon do, the system they chose made sense.

My emphasis.
Shouldn't that be *exorcising*? Merriam-Webster says it means (1b)to
get rid of something menacing. "Get Thee out, bitpim! Get Thee out, MPT!"

By the way, do you know what you get when you don't pay your Excorcist?
You get repossessed.

Via con Dios

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Ted
I wasn't born in Texas but
I got back here as soon as I could
(Don't forget to take out the trash)

No one can make you feel inferior without your consent,
but you'd be a fool to withhold that from your superiors.

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