The principle at the heart of cell phone location tracking is centuries old.(1) The partitioning of a city-scale map into polygon shaped regions dates back to the 17th century and philosopher Descartes. It was perfected in the early 1900s by Russian scientist George F. Voronoi and as a result, is commonly known today as the Voronoi diagram.
Signal Tower Maps
If a cell phone subscriber is using provider company A, then their location can at all times be determined by the position of their cell phone’s transmission signal, or “ping,” in relationship to an overall city map.
For each cell phone provider, a map of the same city can be cut up into small geometric diagrams, with a cell phone transmission tower sitting at the center of each.(2) The precise determination of an individual’s physical location based on their cell phone’s recurring pings involves a lot of complicated mathematical algorithms and nanosecond computerized calculations. But at the heart of the process is the Voronoi diagram, still to this day.
Each cell phone polygon, or sector, generally contains at least one transmit antenna, a pair of receiving antennas, and another operational antenna.(3) It is those two receiving antennas that constantly take receipt of a cell phone’s information, be it an active conversation, data transmission or simple regular “heartbeat”, and relay it back to the provider in question.
In real time, this information can be monitored, processed, and mapped to pinpoint a person’s location. It is the very same technology that is seen in Hollywood thrillers such as the Matt Damon trilogy of Bourne movies.
Each cell phone tower transmitter generally covers an area that is between two and ten miles wide. There are also smaller, targeted towers that may be put in place for a tunnel, or other specific roadway feature. As a cell phone user moves through a region, from one “cell” of the Voronoi diagrammed map to another, their equipment automatically detects and hands off the signal to the next-available strongest receiver.
(1) Wolfram Mathworld – Voronoi Diagrams, Retrieved August 16, 2011 from http://mathworld.wolfram.com/VoronoiDiagram.html
(2) Datalogic Institute – A Visual Implementation of Fortune’s Voronoi Algorithm, Retrieved August 16, 2011 from http://www.diku.dk/hjemmesider/studerende/duff/Fortune/
(3) PrivateLine.com – Cell and Sector Terminology, Retrieved August 16, 2011 from http://www.privateline.com/mt_cellbasics/