The Telephone Zone

Cell Phones


How Cellphones Work – Answering the Call to your Questions

Do you have a cellphone? Or are you considering buying a cellphone? Do you ever think about the technology of a cellphone? Or do you just make that call and take it for granted that it’ll work? Have you ever made a cellphone call to someone on the other side of the world? Did you wonder how that signal traveled all that way around the earth? These are all questions most people don’t ask themselves. Most of us take cellphones for granted. As long as we can talk to who we want, when we want, then we don’t need to be concerned about how the call is made. So we’re going to talk about how cellphones work. We believe that if you have a knowledge of something you’re using, you somehow appreciate it more.

Cellphones – radios, what’s the difference?

Cellphones are actually radios. They broadcast their signals on radio frequencies. So what’s the difference? Let’s compare. First, we’ll look at how radios work. You’re probably familiar with CBs or walkie-talkies. And you probably know that only one person can talk at once, and the frequency is shared by just the two of you. This system of transmitting radio signals on a single frequency is known as a simplex system.

Cellphones operate on a duplex system, which uses two frequencies – one for talking or sending, and one for listening or receiving. That’s the basic difference between radios and cellphones. Another difference worth noting is that CB radios have 40 channels. Cellphones can use up to 1,664 channels. Its obvious that cellphone technology, although basically similar to radio technology, is much more sophisticated.

Cellphones transmit signals over the airwaves

To understand the transmission of radio signals, you’ll need to understand frequencies. Think of the entire width of the airwaves, referred to as the spectrum, as being split up into numerous strips. Each strip is a frequency, capable of transmitting electric currents containing signals. Blocks of frequencies, referred to as the bandwidth, are designated for various transmissions. Cellphones have been assigned a bandwidth in which to transmit their signals. But with the number of cellphones, and the number of calls competing for airtime, something needed to be done to expand their airspace.

Digital technology – an improvement over analog

Because expansion of the airwaves wasn’t an option, cellphone technologists had to come up with another solution. So what they did was split the available bandwidth. And the way they did that was to convert the analog signal into a digital signal. To understand the scope of this change, think of audio cassettes compared to CDs – cassettes are analog; CDs are digital. And look at how much more data you can store on a CD than on a cassette. That’s how cellphones can send more digital signals without interference.

Cellphone signals “get around”

A cellphone transmission does indeed get around. And this is how it goes. Cellular systems are made up of a series of geographical areas, called cells (thus the name of the phone). Within these cells are a number of assigned channels. These channels can be used by different cells, as long as they’re not too close to each other. If two cells were using the same channel at the same time, and if they were too close to each other, they would interfere with each other. That’s why the channels are carefully assigned, so as to minimize interference. So the big advantage to this is that the same channel can be used all across the country, without interference. In that way, use of the available bandwidth is maximized.

The technology behind the transmission of cellphone signals is fairly-easily understood. Remember analog systems, that split their assigned bandwidth into channels; each channel can be used by only one caller at once. The next advancement of this technology digitally splits the calls using different frequencies and times, thus allowing you to transmit three calls within one channel.

Now, the latest digital technology doesn’t use channels at all. What it does, is send out the signals in code, which can be scattered throughout the whole spectrum, using only the piece that it’s currently occupying. The receiver, the cellphone at the other end, can gather up this data by decoding it and translating it back to its original sound – your voice.

And remember that call that goes all the way around the world? It gets there using the same technology that it does to go around the block. The difference is that signals that travel around the world are sent and received by satellite. Satellite technology is touching every part of our lives these days, and cellphones are no exception.

How your cellphone recognizes the caller

When your cellphone is manufactured, it’s assigned an Electronic Serial Number (ESN). This number stays with your phone for it’s whole life. No matter what phone number is actually assigned to your phone, the ESN remains the same. The ESN is important because that’s how the cellphone system knows it’s you that’s placing a call, or that you’re the one someone else is calling.

Every time you phone somebody, a central system identifies you as the caller. The identification process includes making sure your account is in order – like if you’ve paid your bill). If everything checks out, then the system connects you and assigns your signal to any frequency that’s open at the time, and off it goes.

What happens when there’s no signal?

Sometimes, when you’re traveling with your cellphone, you go through “dead spots” where you get a “No Service” message. Remember the cells in each area? Well, these cells are connected by towers that send and receive signals. As you travel, the system automatically transfers your cellphone from one cell to another, so that you’re always in range of a tower. However, there are a few areas where there’s too much distance between towers, usually in remote areas. When you get caught in one of those areas, the signal from your phone cant find a tower to receive it, and you have “No Service”.

This also brings up “roaming”. Your phone is programmed to operate toll-free within a certain area. If you leave that area, the tower that receives your signal doesn’t recognize your phone as belonging to that area. So it makes your connection, notifies you on the display of your phone that you’re “roaming”, and automatically charges you extra for it.

Today’s cellphones are amazing!

So that’s the basics of how cellphones work. And cellphone technology is rapidly advancing. Now you can do all kinds of things with your cellphone. You can send text messages. You can download ring tones. You can even buy a cellphone camera and take pictures with it, which you can then send to your family and friends. As cellphone technology advances even further, you’ll soon be able to operate half your life from your cellphone.

There are hundreds of online cellphone merchants; the Internet has become the place to shop for a cellphone. Check out all the new models and options available. And next time you’re making a call on your cellphone, think of how cellphones work – it’ll make you appreciate it more.

About The Author

Gareth Marples is a successful freelance writer providing valuable tips and advice for consumers purchasing free nokia ring tones, international phone cards, and low cost web hosting. His numerous articles offer moneysaving tips and valuable insight on typically confusing topics.

This article on "How Cell Phones Work" reprinted with permission.

© 2004 - Net Guides Publishing, Inc.

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