Cell tower signal-based technologies

Overview
Since the advent of consumer cellular technology, making and receiving mobile telephone calls has depended on the ability to determine a device's location from the constant radio communication between the device and the mobile carrier's cell towers that are spread throughout the carrier's service area. The ranges of the individual cell towers divide the service area into separate sectors.

As the towers are in fixed positions, determining a device’s current cell tower sector tells the carrier the device's approximate location. The precision of this method depends on how much space a particular tower covers. In general, urban areas have smaller sectors than rural areas because each sector can only manage a certain amount of cell traffic at any one time. Because of increasing cell traffic, the number of cell towers has proliferated to the point that there are now over three times more than there were 10 years ago. As a result, cell sector-based location data are increasingly accurate.

Companies can further improve accuracy by using triangulation methods, which determine location through the mathematical comparison of a device's signals that reach more than one cell tower. Cell tower triangulation can now yield results within 50 meters of accuracy.

Source

 * Mobile Device Location Data: Additional Federal Actions Could Help Protect Consumer Privacy, at 11-12.