Understanding Cell Phone “Pings”
Posted on March 14th, 2010 by JWG
Cell phone pings were an important part of the Caylee Anthony case during the period of time Caylee was first reported missing on July 15, 2008 up to the time her remains were discovered next to Suburban Drive on December 11, 2008. LE and many sleuthers were attempting to use the pings to decode Casey’s movements in an attempt to figure out where she might have dumped the body. After that the pings were pushed into the background while the forensic work on the remains jumped to the foreground. The actual phone calls recorded in Casey’s ATT records continue to come into play.
Recently some uber-sleuthers on Websleuths brought a certain set of pings to our attention once again as possibly being very important to the case. Before I post on what they have uncovered, I want to provide as-brief-as-possible explanation as to how the pings can be used to give a rough idea as to where a person might be. This will provide the necessary background needed to understand how Casey’s location and movements can be inferred.
First, let’s discuss a cell tower’s range. The range depends on a number of factors, such as the tower’s height, the size and power of the transmitters, obstructions (such as buildings, trees, and terrain), and the underlying communications technology supported by the transmitters (CDMA, GSM, etc.). Towers can have a range as short as 2 or 3 miles and as far as 45 miles.
Towers are typically placed such that their ranges overlap, ensuring a clean “hand-off” as a caller moves out of range of one tower and in range of another. Because of this overlap, a tower with a range of 5 miles might carry certain calls for only three miles because another, nearby tower will be close enough to a caller to pick up a call with higher quality. In the greater Orlando area we see towers spaced fairly close to each other such that calls are carried by a tower for only two or three miles in many cases before being passed off to another tower.
Another very important aspect of cell towers is the arrangement of the transmitters. To the left is an image of a tower that does a great job illustrating the typical arrangement of transmitters on a tower. The actual transmitters are not fully visible behind the shielding, but one can see immediately that the tower has two transmitter “layers” and each layer is arranged as an equilateral triangle. Not all towers have two “layers”. Some have one, some have three or more. The number depends on the amount of traffic the tower is intended to handle.
Each tower is responsible for the signals in a circle around its base, up to the specified range. Remember from your high school geometry class that a circle has 360 degrees? Well, because the transmitters are arranged as equilateral triangles, each of the three “sides” are responsible for the signals in a 120 degree sector around the tour’s base.
If you can forgive me for not giving a 100% precise example, here is one example that I hope might make sense. Suppose I have a tower with one set of transmitters facing North. That tower’s three sets of transmitters would then have responsibility for signals in the following directions:
Set one: northwest to northeast.
Set two: northeast to south.
Set three: south to northwest.
Casey’s ATT wireless records released as part of discovery in September, 2008 included the following information:
Date / Time of a call (I will use “call” to refer to both phone calls and texts)
Whether it was an incoming or outgoing call
The number being called (if Casey was being called, she would show here)
The number placing the call (if Casey was calling someone, she would show here)
The duration of the call
The local area code and cell ID
The cell tower latitude and longitude that handled the start of the call
Other less useful pieces of information I won’t get into here
If you don’t mind me going a little off-topic for a moment, please allow me to offer kudos to some hard-working sleuths. When those records were first released some folks went to work getting the scanned documents into a usable form: a spreadsheet. Their sole purpose was to see if they could offer insight into where Casey might have dumped little Caylee’s body. At the risk of missing some key names:
ElizaAvalon did the primary grunt work in using OCR software to convert the scanned copies into pass-1 of the spreadsheet. This was a thankless task as the copies were very noisy and resulted in many, many errors after the conversion process.
ElizaAvalon and TexasLil did the bulk of the quality-control work, manually reading the resulting spreadsheet, comparing with the released documents, and making the corrections by hand.
BondJamesBond added a wealth of bells-and-whistles to the spreadsheet, making it easy to find and sort calls.
GeorgiaPI generated Google maps showing every ping for every day recorded in the records.
Many unnamed people worked to determine who’s numbers were in the cell records, and I humbly submit that their records are far more complete than the records released in discovery.
The manually-generated version of the spreadsheet was in use until April of 2009, when a discovery release was made available that had Casey’s ATT records in spreadsheet form, as provided by ATT. Those records were used to replaced the OCR’d version in the sleuth’s spreadsheet, and are considered spot-on accurate.
Back to the topic at hand. The cell ID (CID) is a piece of data that gives us insight into the direction from the tower a caller was located when they placed / received a call (or text). A CID is 5 digits, such as 12345, but it is the last digit – the “5″ in the example given – that identifies which transmitter was involved in the call.
In a given geographic region, a cell provider will usually try to orient towers such that the last digit of the CIDs are oriented the same. In other words, a provider might ensure all “1’s” point north. This is not a guarantee, and one must check with the provider to be sure of the orientation.
Amateur sleuths don’t have subpoena power, but we have the next-best-thing. Techie sleuths who download obscure applications to their cell phones. One such sleuth – BreatheLife21 – had an application on his ATT phone that would constantly monitor the roaming signal and report the cell ID of the tower the phone was connected to. This sleuth happened to live in Orlando, and he was kind enough to drive around many towers of “Anthony interest” and record where the various cell IDs kicked in. From his various excursions we were able to produce the following diagrams that show the orientation of the Anthony towers of interest (up is north, and the single digit refers to the CID):
Referring to the diagrams above, when the last digit of the CID is “1″, the caller is located somewhere northwest to northeast of the tower. If the CID is “5″, the caller is somewhere north to southeast of the tower.
While the CID helps in narrowing things down quite a bit, it still presents a big target to anyone trying to truly narrow things down with respect to Casey Anthony. Fortunately, Casey helped out here because she used her phone a lot. Here are some rules of thumb we were able to figure out with respect to Casey and the CIDs:
If the tower and CID did not change during a span of 5 to 10 minutes, Casey was probably in one place. And most of those places were logical places, such as Tony Lazarro’s apartment.
If the tower did not change but the CID changed back and forth between the same two numbers, Casey was in one place at a location near the boundary of the two CIDs. This really narrows things. For example, if the CID bounced back and forth between “3″ and “1″, then Casey was northwest of the tower.
If the tower / CID pair changed back and forth between the same two combinations, Casey was in one place at a location near the boundary of the two towers. The Anthony home, interestingly, was at the boundary of three towers and we very often see Casey at home pinging from those three towers for several hours.
If the towers change, we can use that and the CID information to track Casey’s movement. In general I personally stick to major or semi-major routes when doing such analysis, but I accept that lesser-known shortcuts can produce the same results. Nevertheless, the density of cell towers is high enough in the Orlando area to give us a pretty good sense of where she was going and what route she was taking.
Generally I use Google Earth to produce my maps. Early on I was able to take much of the work done by GeorgiaPI and convert it to Google Earth KML files. Thus, on a future post when you see terrain images with routes and ping locations, all of that was done on Google Earth using the hard work of the folks mentioned above.
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