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Wednesday, 25 April, 2001, 09:29 GMT 10:29 UK
How do 3G phones work?
by BBC News Online's technology correspondent Mark Ward

As technology develops it gets harder and harder to work out what has changed when a new gadget or widget goes on sale.

This is especially true of mobile phones. The first mobile phones were as bulky portable and attractive as a breeze block.

Now they are all slinky, shiny and interchangeable. The improvements made to each one only become clear when you start to use them.

Third-generation, or 3G, networks are going to continue this trend. The phones will look the same as ever but the uses to which they can be put will simply explode.

Routing networks

In the old days, when all phones were fixed rather than mobile, making a call involved establishing a direct electrical connection between your handset and the one you were calling.

The same happens with GSM mobiles, but instead of setting up a dedicated circuit, a small portion of the airwaves are reserved for your call.

This is a really bad way of dividing up the available airwaves because it means that the spaces and pauses in speech get the same priority as the words.

3G networks change all this. Instead of reserving airspace each conversation is chopped up into packets, each one of which is labelled with a code denoting which dialogue it is from.

New flavours - high speeds

There are different flavours of these sorts of networks. The flavour that many GSM networks are expected to adopt is known as Universal Mobile Telecommunication Services (UMTS), but the US is adopting a different flavour in a move that could preserve existing incompatibilities.

This radical change means 3G mobile networks can support lots more subscribers and let them download data much faster. On current GSM networks data chugs around at 9.6 kilobits per second (kbps).

By contrast the upper limit for 3G networks is 2 megabits per second if you are standing still and 384 kbps for those on the move.

These are maximum rates and possible speed will fall as more people download data in any particular cell. It is possible that at peak times phone users will be lucky to do better than the 56kbps possible over a fixed phone.

Always connected

Using packets of information to carry voice and data also means that your phone is effectively always connected to the network. This means that SMS messages, e-mails, video clips, or whatever can be delivered any time, you don't have to dial-up to check mail.

This will mean a huge change in the way that you pay for your phone. Mobile operators will have to stop charging on the basis of talk time and move to a model based on the packets you download or a single charge per month covering anything and everything you do.

The move to 3G networks means you will be able to do many more things with your mobile phone. It could become a wallet holding train or cinema tickets, discount vouchers for shops or even a key to unlock your house.

Handset problems

All these extra tasks will put something of a burden on the handset. At the moment screens on phones are small, they are difficult to type or get data into and they typically only work with one mobile phone technology.

Third-generation networks might require bigger screens, especially if you download video clips, better ways to move data in and out of them, and bigger memories if you want to carry your MP3 files with you.

The handsets themselves are likely to get slightly bigger to hold batteries to support these new uses and to include chipsets for existing mobile networks as well as the new ones.

Until UMTS is ubiquitous you'll be forced to use the best network available in your location. Because the cells that make up 3G networks are much smaller than those of existing network technologies you could be stuck with your 2G phone outside the big cities.

The day of 3G may be dawning but it will be a long time before the sun sets on our existing mobile phones.

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