Oct 24 2014

More Than You Ever Wanted to Know about Cell Tower Technology

By Dana Chivvis

This seems like a good time for a primer on cell tower technology. This is basically all you need to know to make some sense of that call log we published yesterday.

First, cell towers have three sides: an A side, a B side, and a C side. Think of a pie with three slices. Each of those slices has a range. When a person is in that range and makes a cell phone call, the cell phone will talk to that side of the cell tower. So if you look at the call log, you’ll see some calls are noted as “L651A” or “L651C.” Same cell tower, different side. Generally speaking, the A side of the tower points north or northeast, the B side points south or southeast, and the C side points west.

Adnan's cell phone call log

The engineers who run these cell phone networks, like Abe Waranowitz, who testified at Adnan’s trial, can map out the basic ranges of all the towers in their network. These maps aren’t precise though, because a cell tower’s range can depend on a variety of factors. Foliage, for example, or buildings or hills can cast a shadow on the cell tower’s range. Plus, some cell towers have overlapping ranges. So you can be in one place and make a phone call and that phone call can trigger either cell tower. Not both cell towers, but one or the other.

Because the range maps aren’t precise, the prosecutors in Adnan’s case asked Waranowitz to do an origination test at a bunch of locations that were important to the case. What this means is that Waranowitz went to each location - the burial site, for instance, or the Park and Ride - and then made a cell phone call using special equipment. This equipment told him which cell tower was triggered by the call. In Leakin Park, at the burial site, it was L689B. At Gilston Park, it triggered L698A, L698B and L654C. But Waranowitz noted that L654C was the strongest signal there because of a mound of dirt in the park, which would have obstructed the other two.

CORRECTION: Earlier I wrote that the origination test at "Gelston Park" triggered L698A, L698B, and L654C. The place is actually called "Gilston Park." Well, officially it's Westview Neighborhood Park. This park stuff is a little strange. There is a Gelston Park, east of this one, sort of close to where Hae's car was found. But the park where Abe Waranowitz did this origination test - Westview Neighborhood Park - is west of I-695, off of Gilston Park Road. So it's referred to as "Gilston Park."

Follow Serial