| Cell phone
calls to 9-1-1 have come a long way since the days when we had no
information about you or your actual location.
As of May 2005 we have Phase II 9-1-1
service with all cell phone companies (carriers).
Scroll down for a description
of how your location is determined. |
Want to Learn
More?
Federal Communications Commission
-
Many good links and resources
General Overview of 9-1-1
- at FCC site
Alabama Wireless Board
This group administers Wireless 9-1-1
in Alabama
Alabama Chapter of NENA
Our professional association, many good links.
ALNENA Wireless Page
National NENA -
Wireless Section |
| With Phase II
phones we get the latitude - longitude of the caller within the
requirements of the FCC rules.
Accuracy
Standards: The FCC
adopted the following revised standards for Phase II location accuracy
and reliability:
-
For
handset-based solutions: 50 meters for 67 percent of calls, 150 meters
for 95 percent of calls;
-
For
network-based solutions: 100 meters for 67 percent of calls, 300
meters for 95 percent of calls.
Phase II is
is not available in all areas when you travel...
There will
be errors in locations as noted above...
Be
prepared to give a location to the 9-1-1 Dispatcher!
Look around for
landmarks, street signs, mile markers, addresses on mailboxes, store
names, or anything else that will help us locate the emergency. |
|
|
Simplified
Description of Location Determination Technologies |
|
|
Handset or GPS Based Location |
Network or Triangulation
Location |
| |
|
The GPS system consists of 24 earth-orbiting satellites. A chip
embedded in the wireless phone receives signals from three or more
satellites and calculates the location as described below. |
 |
|
1 |
2 |
3 |
|
A Chip-equipped phone
measures the amount of time it takes for a satellite's radio
signal to reach the phone.
Since the speed of
radio signals is known, the distance from the satellite can be
calculated. |
The phone then
measures the time for a second satellite's signal to reach the
phone.
The phone is at
one of the two points where the first and second circle overlap. |
When the phone can
receive a signal from three or more satellites the location
becomes precise.
The location must
then be transmitted to the 9-1-1 center and displayed on a map so
the Dispatcher can determine the proper responders. |
|
|
The towers can be existing cell-phone towers, water tanks, tall buildings,
or other locations where receiving antennas can be mounted.
| Using the
known speed of radio signals, the distance from receivers can be
calculated. It takes at least three and preferably four to get a good
location. |
 |
|
