Cell-companies today provide location-based services.
I would like to know how accurate is the location they can get (on
handsets that don't have a built-in GPS).
Is it a few meters? miles? track the cell you are connected to and
that's it?

Thanks.

Depends on the system:

from my notes:

3G Mobile
The Third-Generation (3G) Mobile World Summit-Asia Pacific
15-18th January 2002. Makuhan Messe (Nippon Convention Center)
Tokyo, Japan

Day 2 – Wednesday 16th January 2002
15:20 Chris Wado (Cambridge Positioning Systems)
-Location keeps families safe (i.e. emergency services know where you
are)
-North America requires all mobile operators to provide location data
to 911 emergency dial
-CPS delivers and licenses solutions to find you
-Competing technology GPS
-CPS uses E-OTD – Enhanced Observed Time Difference
-E-OTD is cheaper than GPS

Using 2G, achieved:
-24 meter trials in N. America
-36 meter trials in Europe
-12 meter trials in Asia Pacific
-EOTD requires hardware in base station and software in handset
-presently too expensive, working to reduce cost by eliminating
hardware

Drivers:
-Safety
-Corporate asset management
-Commercial buddy-finder (where are my friends now)
-Nearest hospital, cheapest gas station, etc.

-2G stations are different channels, so stranger signals don’t drown
out different stations
-3G is more challenging, weak signals drowned out by strong signals
-CPS breakthrough: RSSI software blanking
-Cumulative Virtual Blanking

Also see web site of Cambridge Positioning Systems:

CPS product and service overview:
http://www.cursor-system.com/products_services.asp

---

Request for Answer Clarification by ga4-ga on 12 Mar 2003 08:21 PST

I'm really sorry, but this does not answer my question.
It's a few notes about the trials of a specific solution (which looks
like is not widely used).
I know that TODAY there are location-based services in all major
operators, including custom-applications like allowing a company to
follow it's car-fleet, 911 applications etc.
My question was "...how accurate is the location they can get?...Is it
a few meters? miles?..."

Thanks again.

---

Clarification of Answer by maxhodges-ga on 12 Mar 2003 08:42 PST

ga4-ga,

Thank you for providing me with an opportunity to clariy my answer;
however, after requesting a clarification you immediately rated my
answer, which left me no time to respond to your request.

The information you are seeking is on the web site of the link I
provided:

"Cursor™ is a standards-compliant high accuracy mobile location
technology using the E-OTD (Enhanced Observed Time Difference) method.
Cursor™ technology can deliver accuracy results of 50m on GSM
networks, with even greater accuracy predicted for 3G (3rd
Generation)."

From CPS Web Page, How Cursor Works:
http://www.cursor-system.com/tech_how_cursor_works.asp

"...CPS has developed a new technology that will deliver sub-20 metre
accuracy.

"...Cumulative Virtual Blanking (CVB) builds on our innovatory work in
E-OTD to offer a simple to integrate solution for the wideband
wireless environment.

How it works:
Within current industry standards, E-OTD (or OTDOA as its known in 3G)
faces a challenge - that of “hearability", because the same radio
frequencies are used by base stations. Because measurements are needed
from three base stations, this can mean that distant signals can be
drowned out from nearby base stations.

Currently, the proposed solution is to use an Idle Period on the Down
Link (IP-DL), a way of momentarily turning off each network
transmitter in turn to allow a mobile handset to generate enough
location measurements to determine precise location. However, turning
off transmitters in turn needs coordination in the network, adds
complexity to the handset, and leads to a reduction in network
capacity.

CPS' 3G solution CVB removes the need for IP-DL and successively
blanks each signal in turn from the location calculation - without
physically switching off any of the network."

CPS Cursor 3G:
http://www.cursor-system.com/products_3g.asp

CPS the world leader in this market. You might be interested in their
white papers if you wish to understand this technology in detail:

CPS White papers:
http://www.cursor-system.com/innovations_doclibrary.asp

---

Clarification of Answer by maxhodges-ga on 12 Mar 2003 09:12 PST

Final note: wireless location performance varies widely depending on
hardware, software, landscape, weather, etc.

Here is another technology you might be interesting in knowing about:

SnapTrack Performance
http://www.snaptrack.com/Advantage/performance.html

I'm really sorry, but this does not answer my question. 
It's a few notes about the trials of a specific solution (which looks
like is not widely used).
I know that TODAY there are location-based services in all major
operators, including custom-applications like allowing a company to
follow it's car-fleet, 911 applications etc.
My question was "...how accurate is the location they can get?...Is it
a few meters? miles?..."

Just a suggestion, but perhaps the researcher could have turned his
"notes" into an intelligible answer. Something phrased in complete
sentences might have been nice.

The rate was a newbie mistake (premature e-rate-culation). How can I change it?

While it is courteous that you wish to reconsider your prior rating,
there is no mechanism for changing a rating once it has been given.

Don't worry, though, about not understanding the system. The system
permits customers to rate an answer prior to asking for clarification.
While we researchers have fragile egos, and thus like to see lots of
stars given for the answers we provide, you didn't do anything wrong.

The answers provided, as ga4 indicates, talk about possible ways very
accurate positioning could be obtained from cellphone networks. As far
as I am aware no operator has actually started using these
technologies commercially (which rely on triangulation and / or time
delay) to provide location based services.

The services that are available today rely only on the cell that the
phone is in.

They work like this. The phone company maps the normal service area of
each cell of its network, taking into account geographical variations
and base station antenna performance, power and directionality. The
central point of this coverage area is then taken to be the location
of the phone. Where companies sell location information to content
providers (eg maps, directories etc), they will provde an x,y
coordinate corresponding to the middle of the cell. They do not
provide information about the size of the cell, nor its shape, as this
is commercially sensitive. However, they will share this information
with emergency services if asked to locate a phone (eg they will give
emergency services an indication of the likely accuracy, whereas
commercial partners do not get this information).

The accuracy therefore is dependent on the size of the cell. In urban
areas cells may only be 100m or so in size, so accuracy is quite high.
In rural areas cells can be ten kilometers or so accross, so clearly
accuracy is very low.

Cell phone companies will usuaally store information about which cell
each call was made or received was in. The may vary by country, as it
is often a regulatory requriement. However, it is normal that a cell
phone company stores this information for several months, and can
provide this information to emergency services given the correct
authorisation. There is no way as a consumer to hide or withold this
information (although your cell phone network may allow you to
withhold your location from commercial partners who provide LBS).

Methods of improving the accuracy, as Maxhodges indicates, rely on
triangulating the phone from several masts. This requires software
both on the network and the phone that supports the service.

It may be posisble to improve the accuracy of the location without
needing new phone software by examining the power level that is output
from the base station. The base station (and the phone) will gradually
increase their radio output level in order to get an acceptable
signal. It woudl be possible to make an assumption about how far the
phone was from the base station by using this information, although it
would of course be subject to errors (for example a phone may simply
be in a basement, rather than a log way away from the mast). As far as
I know no network is using this information in its LBS products.



You can get more information about LBS services is Europe by signing
up to Vodafone's developed forum - http:/via.vodafone.com. There are
some documents avaiable to potential providers of LBS services that
may be useful. I don't have informaton about the situation in the US,
but I have no reason to suppose it is very different.