I’m sure you have seen them. Up and down highways, tucked into corners of farmland, or maybe even right in the center of your town. Cell towers are everywhere and as most people know, they are essential to our everyday communication with our mobile phones. But have you ever wondered how exactly these towers work together to provide a blanket of coverage so you don’t lose your signal, even while moving at high speeds down the interstate?
How do we get our cell network? Think about a cordless phone you may use inside your home or office. There is a base station that is connected to your phone line and a cordless device that allows you to roam within a certain distance of that base station. For all intents and purposes, our cell networks are comprised of a plethora of cell sites or towers that work in a similar manner to your cordless phone base stations. These cell towers are built to provide service to our cell phones with, of course, much greater range and strength to withstand the variety of factors that stand between the tower antennas and our mobile devices.
A typical tower cell site consists of a number of antennas mounted at some elevation off of the ground (generally about 50-200 feet) and antenna feed-lines running to base station equipment protected by outdoor cabinets or a shelter at ground level. Most cell towers have three directional sectors that the tower top antennas service. These three sectors help form a network of “cells”, or a geographic coverage area. The tower locations are carefully selected to provide optimal coverage without too much overlap of coverage cells. A gap in coverage can serve as an indication to cell carriers that maybe they should investigate a new cell site to service that coverage gap.
What is the range of the cell tower signal? Although it is commonly thought that the coverage of one tower with directional antennas looks like a large circle with a 1-2 mile radius made up of three 120° wedges, cellular experts say that the coverage of one tower looks more like a blob [click for image] than a circle. They have also said that in some instances, one sector of antennas may reach up to 20 miles. Signals can be blocked by topography, and other obstacles, creating dead service pockets that may be picked up by another nearby tower. When a mobile device is in range of more than one tower, an algorithm may be used to select the service tower based on signal strength and current traffic of each tower.
The telecommunication industry is ever-developing and has started implementing “small-cell” sites that may not have the great range of a standard “macro” cell tower, but they serve a variety of purposes. Small-cell sites allow us to keep a strong signal even when we are attending an event with a high-density population or inside of a large office building. Additionally, these small-cell sites allow the carriers to provide more capacity, by creating an alternate space to offload some of their “macro” network traffic.
From New York City to San Francisco, cell towers are working together in one big network to make sure you have the service you need. Now hopefully next you pass one of these towers with a friend, you can enlighten them a bit on how they actually work!
About James Marooney, PE
James Marooney, PE, is a Regional Leader for Wireless Services in Washington D.C. at Foresite Group. He graduated from University of Maryland with his Bachelor’s degree in Civil Engineering and a minor in Project Management. James enjoys working with a communicative team in order to get the job done on time. He has a special interest in working with a variety of carriers, especially learning how each carrier implements their systems and methods to complete a job.