Custom Search

Cellphones (Mobile phones)

Nokia cellphone with keypad extended

Last updated: May 22, 2009.

Walking and talking, working on the train, always in contact, never out of touch—cellphones have dramatically changed the way we live and work. No one knows exactly how many little plastic handsets there are in the world, but the best guess is that the total is approaching one billion. That's almost one for every six people on the planet! In developing countries, where large-scale landline networks (ordinary telephones wired to the wall) are few and far between, over 90 percent of the phones in use are cellphones. Cellphones (also known as cellular phones and, chiefly in Europe, as mobile phones or mobiles) are radio telephones that route their calls through a network of masts linked to the main public telephone network. Here’s how they work.

Photo: A typical Nokia cellphone.

Cellphones use wireless technology

Typical Motorola flip cellphone

Photo: A simple Motorola cellphone from the late 1990s.

Although they do the same job, land lines and cellphones work in a completely different way. Land lines carry calls along electrical cables. Cut out all the satellites, fiber-optic cables, switching offices, and other razzmatazz, and land lines are not that much different to the toy phones you might have made out of a piece of string and a couple of baked bean cans. The words you speak ultimately travel down a direct, wired connection between two handsets. What’s different about a cellphone is that it can send and receive calls without wire connections of any kind. How does it do this? By using electromagnetic radio waves to send and receive the sounds that would normally travel down wires.

A man using a cellphone in a street in Iraq

Photo: Phones to go: you can use a mobile phone wherever you can get a signal, even in war-torn Iraq. Photo by Tammy Grider courtesy of Defense Visual Information Center (DVIC).

Whether you're sitting at home, walking down the street, driving a car, or riding in a train, you’re bathing in a sea of electromagnetic waves. TV and radio programs, signals from radio-controlled cars, cordless phone calls, and even wireless doorbells—all these things work using electromagnetic energy: undulating patterns of electricity and magnetism that zip and zap invisibly through space at the speed of light (300,000 km or 186,000 miles per second). Cellphones are by far the fastest growing source of electromagnetic energy in the world around us.

How cellphone calls travel

When you speak into a cellphone, a tiny microphone in the handset converts the up-and-down sounds of your voice into a corresponding up-and-down pattern of electrical signals. A microchip inside the phone turns these signals into strings of numbers. The numbers are packed up into a radio wave and beamed out from the phone’s antenna (in some countries, the antenna is called an aerial). The radio wave races through the air at the speed of light until it reaches the nearest cellphone mast (often mounted on a hill or tall building).

The mast receives the signals and passes them on to an exchange building, from where they are routed onward. Calls made from a cellphone to another cellphone on the same network travel to their destination by being routed to the mast nearest to the destination phone, and finally to that phone itself. Calls made to a cellphone on a different network or a landline follow a more lengthy path. They have to be routed into the main telephone network before they can reach their ultimate destination.

Photo: Engineers repair a cellphone mast. Photo by Brien Aho courtesy of US Navy.

How cellphone masts help

Cellphones are a bit like two-way radios. A cellphone handset contains a radio transmitter, for sending radio signals onward from the phone, and a radio receiver, for receiving incoming signals from other phones. Because the radio transmitter and receiver are not very high-powered, cellphones cannot send signals very far. This is one reason why cellphone masts are necessary: with their huge high-powered antennas, they can pick up faint signals from many cellphones and route them onward to their destination. If we didn’t have masts, we’d need cellphones with enormous antennas and giant power supplies—and they’d be too cumbersome to be mobile.

What cells do

There’s another reason for having masts too. Suppose several people in your area all want to use their cellphones at the same time. If their phones all send and receive calls in the same way, the signals would interfere and scramble together and it would be impossible to tell one call from another. One way to get around this is to use different radio waves for different calls. If each phone call uses a slightly different frequency (the number of up-and-down undulations in a radio wave in one second), the calls are easy to keep separate. They can travel through the air like different radio stations that use different frequency bands.

That’s fine if there are only a few people calling at once. But suppose you’re in the middle of a big city and millions of people are all calling at once. Then you'd need just as many millions of separate frequencies – more than are usually available. The solution is to divide the city up into smaller areas, with each one served by its own cellphone mast. These areas are called cells and they look like a patchwork of invisible hexagons. Each cell has its own mast and all the calls made or received inside that cell are routed through its mast. Cells enable the system to handle many more calls at once, because each cell uses the same set of frequencies as its neighboring cells. The more cells, the greater the number of calls that can be made at once. This is why urban areas have many more cells than rural areas and why the cells in urban areas are much smaller.

How cellphone cells handle calls

Artwork showing how cells work in a hexagonal arrangement

This picture shows two ways in which cells work.

If a phone in cell A calls a phone in cell B, the call doesn’t pass directly between the phones, but from the first phone to mast A, then to mast B, and then to the second phone.

Cellphones that are moving between cells (when people are walking along or driving) are regularly sending signals to and from nearby masts so that, at any given time, the cellphone network always knows which mast is closest to which phone. If a car passenger is making a call and the car drives between cells C, D, and E, the phone call is automatically "handed off" (passed from cell to cell) so the call is not interrupted.

Types of cellphones

The first mobile phones used analog technology. This is pretty much how baked-bean can telephones work too. When you talk on a baked-bean can phone, your voice makes the string vibrate up and down (so fast that you can’t see it). The vibrations go up and down like your voice. In other words, they are an analogy of your voice—and that’s why we call this analog technology. Some landlines still work in this way today.

Cellphones abandoned by students before an exam

Photo: No cheating! These naval reservist students had to check in their phones before sitting an exam. Photo by Brien Aho courtesy of US Navy.

Most cellphones work using digital technology: they turn the sounds of your voice into a pattern of numbers (digits) and then beam them through the air. Using digital technology has many advantages. It means cellphones can be used to send and receive computerized data. That’s why most cellphones can now send and receive text (SMS) messages, Web pages, MP3 music files, and digital pictures. Digital technology means cellphone calls can be scrambled using a mathematical code before they leave the sender’s phone, so eavesdroppers cannot intercept them. (This was a big problem with earlier analog phones, which anyone could intercept with a miniature radio receiver called a scanner.) That makes digital cellphones much more secure.

The world of cellphones

Cellphones are changing the way the world connects. In the early 1990s, only one per cent of the world's population owned a cellphone; today nearly a quarter of people make their phone calls this way. In developing countries, there are on average only five telephones (either landlines or cellphones) per hundred people and cellphones are much more popular; in Cambodia, over 90 percent of all phones are cellphones.

Cellphones are also used in different ways around the world. In the United States, mobiles are still mostly used for voice conversations. In Europe, more people send "texts" (text messages, also known as SMS) from mobile phones than use the Internet on personal computers. In Asia, where high-speed "third-generation" (3G) mobile networks and cutting-edge phones are more widely available, more people surf the Web and send emails from mobile phones than in any other way; over a quarter of all Japanese people now use the Internet like this.

A mobile broadband dongle (USB HSDPA modem)

Cellphones and mobile broadband

If you want to find out how cellphone networks have evolved from purely voice networks to form an important part of the Internet, please see our separate article on mobile broadband. It also covers all those confusing acronyms like FDMA, TDMA, CDMA, WCDMA, and HSDPA/HSPA.

Photo: Mobile broadband with a USB modem is an increasingly popular form of wireless Internet.

A brief history of cellphones

How did we get from landlines to cellphones? Here’s a quick history:

1873: British physicist James Clerk Maxwell (1831-1879) published the theory of electromagnetism, explaining how how electricity can make magnetism and vice-versa.
1876: American inventor Alexander Graham Bell (1847-1922) invented the telephone. Later, Bell developed something called a "photophone" that would send and receive phone calls using light beams. It was really a distant ancestor of the mobile phone.
1888: German physicist Heinrich Hertz (1857-1894) made the first electromagnetic radio waves in his lab.
1894: British physicist Sir Oliver Lodge (1851-1940) sent the first message using radio waves in Oxford, England.
1899: Italian inventor Guglielmo Marconi (1874-1937) sent radio waves across the English Channel. By 1901. Marconi had sent radio waves across the Atlantic, from Cornwall in England to Newfoundland.
1906: American engineer Reginald Fessenden (1866-1932) became the first person to transmit the human voice using radio waves. He sent a message 11 miles from a transmitter at Brant Rock, Massachusetts to ships with radio receivers in the Atlantic Ocean.
1920s: Emergency services began to experiment with cumbersome radio telephones.
1940s: Mobile radio telephones started to become popular with emergency services and taxis.
1946: AT&T and Southwestern Bell introduced their Mobile Telephone System (MTS) for sending radio calls between vehicles.
1960s: Bell Laboratories (Bell Labs) developed Metroliner mobile cellphones on trains.
1973: Martin Cooper (1928-) of Motorola made the first cellphone call using his 28-lb prototype DynaTAC phone.
1975: Cooper and his colleagues were granted a patent for their radio telephone system.
1978: Analog Mobile Phone System (AMPS) was introduced in Chicago by Illinois Bell and AT&T.
1982: European telephone companies agree a worldwide standard for how cellphones will operate, which is named Groupe Speciale Mobile and later Global System for Mobile (GSM) telecommunications.
1984: Motorola DynaTAC becomes the world’s first commercial handheld cellphone. You can see a picture of it.
1995: GSM and a similar system called PCS (Personal Communications Services) were adopted in the United States.
2001: GSM had captured over 70 percent of the world cellphone market.
2000s: Third-generation (3G and 3.5G) cellphones were launched, featuring faster networks, Internet access, music downloads, and many more advanced features based on digital technology.