Fairly long article about being traced by cell phones with, and without GPS systems. This is the part of the article that explains how the Kim family was located. The rest of the article is very informative.
Turning cell phones into lifelines
http://news.com.com/Turning+cell+phones+into+lifelines/2100-1039_3-6140794.htmlAlways connected
So how does it all work? Mobile devices, when they are within range, constantly let cell towers and the mobile switching center, which is connected to multiple towers, know of their location. The mobile switching center uses the location information to ensure that incoming calls and messages are routed to the tower nearest to the user.
If a subscriber is unable to get service, this location information is usually purged from the mobile switching center. But some location information may remain in call detail records. Some mobile operators may store the most recent communication between a device and a mobile switching center for a certain period of time, usually 24 hours.
When someone is missing, even this small bit of information can prove useful in determining the approximate location of a device using the updates from the mobile switching center. If the mobile subscriber is still within cell phone range, authorities can track his or her general movement by following the sequence of towers the phone has contacted or pinged. And if the cell phone goes out of range or runs out of battery power, the mobile operator may be able to use the last recorded location before the cell phone either lost its signal or lost power.
But the most useful information for locating people when they are lost comes when someone has initiated or received a call or text message on their phone. Mobile operators keep records of these events for billing purposes in what is known as a call data record, or CDR. And they can go back to these records to get a historical account of the cell phone's location.
This is actually what authorities used to locate the Kims' phone, according to Eric Anderson, director of engineering for Edge Wireless, a regional mobile operator that provides cellular phone service in the area where the Kims were stranded. One of Edge Wireless' cell phone towers briefly connected with one of the family's phones at about 1:30 a.m. November 26 near Glendale, Ore. The phone was connected long enough to the network to send a notice that there was a voice mail or text message waiting. But the connection didn't last long enough for the Kims to retrieve the message or initiate a call for help.
Still, the connection was long enough that two Edge Wireless engineers, Eric Fuqua and Noah Pugsley, were able to find this information in the CDR to determine that the family was in sector "Z" in the southwestern portion of the cell site's 26-mile radius. Wolf Peak's "Z" sector provides coverage to remote areas with little population and very little cell phone traffic. Using this information, authorities sent out rescue teams, which eventually located Kati Kim and her children.
Anderson said that the family was lucky that they were Cingular Wireless subscribers. Edge Wireless uses the same GSM network technology that provides roaming coverage to Cingular customers. If the Kims' phone had been with a different provider that didn't have roaming coverage with Edge Wireless, then the company might not have received any signal at all after they left the major highway, and the cell phone would have been of little use to authorities trying to rescue them.
"Where the Kims' car was found was on the fringe of our coverage area as it was," Anderson said. "So it was a miracle that the phone was able to lock onto the network at all."
Anderson said that if people ever find themselves in a similar situation--lost and having difficulty getting cell phone reception--they should search for the highest ground or area that may be in the line of sight to a tower. They should hold the phone away from their bodies or high so it has no obstructions to a possible tower. It may take up to two or three minutes for it to synchronize or connect with the cell tower and mobile switching center. Even if they can connect for a second or two, it could be long enough to register a voice mail or text message, which could ultimately help wireless engineers track their location.
