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Mobile telephones

Mobiles phones have changed our lives since the first ones appeared in 1985. Today's mobile phones are triumphs of miniaturisation - there's nothing else you own that's likely to fit so much technology into such a small package.

It's a great combination of electronics and design, but what makes it work behind the scenes is just as important. The widespread use of mobile phones has meant huge additions to the old telephone system in the form of base stations, transmitters and antenna towers, as well as clever techniques for getting the most out of the electromagnetic spectrum. And the network also has to know where you are ...

Cells and base stations

Cells and base stations : wireless on the move

Mobile telephone networks are organised in geographic cells, and each cell has an antenna that transmits to all the mobile phones that are in its geographic area. For this reason the network must know exactly where you are as you move around.

When you move from one cell to another your identity (which is contained inside your SIM card) and your new location are automatically reported to the network's control system. Your telephone also 'reports in' to the local network every couple of minutes. You can sometimes hear the communication, as interference, if your mobile is near a loudspeaker or landline telephone.

Conversations on the move are transferred without a break from one base station to the next. And because the network knows at all times where you are (as long as you're in range of one of its base stations and switched on), you can always be contacted if someone calls you.

Frequency allocation and reuse

Frequency allocation and reuse : getting the most from the electromagnetic spectrum

Each network operator - such as Vodafone, 02, Orange and so on - has been given a share of the electromagnetic spectrum - a band of frequencies - for their network and their customers. But this band is not enough to give everyone a permanent connection, so advanced techniques are used to make sure that it's all being used as well as it can be, to ensure there's a slot available when you want to make a call.

When you make a call you're allocated a channel - a small part of the frequency band - but it's not permanent. When you move around and change from one cell to another this frequency may not be available, so you are changed to a vacant slot. And when you finish the call, the slot you've been using is made available for someone else. This is called frequency reuse and the concept forms the basis of having a workable cellular system. Unfortunately there's a fixed maximum capacity for each cell so sometimes you can't get a connection when all frequecy slots are already in use.

Inside your mobile phone : which bit does what?

Inside your mobile phone : which bit does what?

How the cell system works

How the cell system works
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