Nuts and bolts look at how cell networks work

  • Hundreds of cell towers dot the Central Florida landscape, including this cross behind the Gracepoint at the Cross church in Orlando.
Hundreds of cell towers dot the Central Florida landscape,… (JACOB LANGSTON/ORLANDO…)
October 11, 2010|By Sarah Lundy, Orlando Sentinel

We rely on our cell phones for nearly everything — from calling mom or dad to sending funny photos to friends or pounding out work memos over lunch.

But how does it all work? AT&T recently gave the Orlando Sentinel a behind-the-scenes look at its cell-phone technology and network. Here's what we learned.

The backbone of the system is the hundreds of cell towers spread throughout Central Florida.

Often built by a third party, the towers can hold antennas for various wireless carriers, such as AT&T, T-Mobile and Verizon. They share space on a tower, which can vary between 50 feet to 150 feet or higher in rural areas.

Towers can stand alone or be disguised as flag poles, trees or church steeples. Antennas can be added to rooftops in high populated areas. For example, AT&T added more antennas around the new Amway Center in preparation of all the people using their cells outside the building. The company installed an in-building system to handle traffic inside the arena.

The data speed and voice quality of your connection can be affected by signal strength. This can be impacted by distance to a cell tower and how many people are using the tower at the same time.

Your cell phone sends radio-frequency signals to a cell tower's antenna, which then sends it through wires within the tower to cell site inside a small building near the tower's base. Each carrier attached to the tower will have its own building.

A phone call and a photo being e-mailed follow the same path.

If you have a 2G cell phone (the second-generation mobile network), your signal will go to specific 2G channels, which are stored inside a box.

From there it's sent — via copper telephone lines or fiber optics — to another building called a wireless switching office. They are usually nondescript buildings the location of which are often kept hush-hush for fear of network sabotage.

At the switching office, the phone call follows one platform while the data, such as the e-mailed photo, takes the path on another.

Earlier this year, Verizon Wireless finished construction on a 45,000-square-foot switching building in South Florida. The hurricane-hardened, $50 million facility became the call-processing hub for Broward, Miami-Dade and Monroe counties.

The switching office holds the "brains" of the wireless systems and routes your call to where it's supposed to go — wireless or landline — all in a matter of seconds.

A 3G cell phone (the third-generation mobile networks and used by most cell phones today) operate on different types of channels that have more bandwidth, which is how more information can be transmitted.

Wireless carriers are prepping for the fourth-generation of mobile networks. Nextel Sprint kicked off its 4G technology earlier this month.

It will have even more bandwidth to provide faster transmissions of data, such as downloading a photo, sending an e-mail or browsing online. Many wireless companies are prepping their cell sites for 4G.

If you are moving about, such as in a car, your cell signal is transmitted from one antenna to another attached to a second cell tower, which will continue to transmit the signal through a site and to the wireless switching office. All the wireless providers have their own switching offices throughout Florida.

Your call is transmitted from one switching office to the switching office nearest to the person you are calling — no matter if that person is across the street or halfway around the world. That switch will send your signal to a cell tower nearest to the person you are calling.

The next part is easy. Say, "hello.''


Dropped calls

Dropped calls are annoying and can occur for various reasons.

•The cell tower handling your cell-phone signal is overloaded with other voice and data transmissions. That basically means it can't handle your call at that moment.

•Equipment failure at the cell site.

•Obstructions, such as mountains, trees or dense concrete buildings, can cut off the signal to the nearest cell tower.

•Your cell-phone power is too low to keep a signal.

•There's an outage because of weather or problems with the wireline network, such as construction worker cutting the fiber optics cable that connect the cell site to the switch building.

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