FORGET the concept of the phone. And while you鈥檙e at it, forget about phone
numbers, too. Both will vanish when the third-generation mobile phone networks
arrive in the next year or two. Your mundane mono-tasking mobile will be
replaced by do-everything devices more like the communicators of Star
Trek.
The big idea behind 3G is to give you 鈥渢he same services on mobiles as you
get on desktop computers today鈥�, says H氓kan Eriksson, head of research at
Swedish cellphone maker Ericsson. On your mobile you鈥檒l be able to watch colour
video, download CD-quality music from your collection at home, buy a plane
ticket, send e-mail, browse the Web, use positioning services鈥攁nd make
old-fashioned phone calls, too.
To make all that happen 3G networks will need to run a lot faster than
today鈥檚 inefficient GSM digital cellphone system. GSM sets up a dedicated
channel for every call鈥攚asting a lot of valuable transmission capacity.
And sending or receiving data on this single channel can be painfully slow, as
any WAP user knows.
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Pass the parcel
The 3G networks will be much more flexible. They will send signals from many
mobiles over a single channel, moving voice, text, video and audio using a
technique called packet switching鈥攖he same way data is sent around the
Internet. Packet switching slices up information into packets of data that are
sent as separate chunks to their destination. Every packet is treated like a
parcel going through the postal system: it is routed through the network
according to the address written on its front. Because of this, says Eriksson,
we will have Internet-style addresses instead of phone numbers. Your phone will
be like an e-mail box or a website, with its own unique address.
Doing things this way means that when a 3G mobile is switched on, it will be
like an 鈥渁lways-on鈥� Internet connection鈥攑ermanently ready to use. This
will revolutionise the way we pay for the service. 鈥淐harging will not be per
minute, it will be per byte or per data packet. If you don鈥檛 send anything, you
don鈥檛 pay anything,鈥� says Jan Uddenfeldt, chief technology officer at Ericsson.
Again, it鈥檚 like the postal service, Eriksson adds. 鈥淵ou don鈥檛 pay to have a
mailbox on your front door鈥攜ou only pay when you send a letter.鈥�
Japan has already had a taste of always-on technology with its hugely
successful鈥攂ut very slow鈥攊-mode system.
Right now, GSM is being upgraded to a system called the General Packet Radio
Service. GPRS gangs together GSM channels to move data packets fast. 鈥淕PRS
mobiles can handle up to 100 kilobits per second,鈥� says Uddenfeldt. 鈥淚n fact it
may be limited to 56 kilobits per second, like standard PC modems. But that鈥檚
still four or five times faster than a WAP user gets today鈥攁nd it鈥檚 coming
out this year.鈥� GPRS speeds will be limited by the need to keep down the
radiation dose to the head and to stop overheating
(快猫短视频, 7 October, p 21).
An enhanced version of GPRS, called EDGE, due out in two years
time, will push speeds up to 380 kilobits per second.
But GPRS and EDGE will be left standing by 3G devices. Each will have access
to a 5-megahertz channel, against GSM鈥檚 puny 25 kilohertz. 鈥�3G will ultimately
provide users up to 2 megabits per second,鈥� claims Uddenfeldt. 鈥淓ven in the
early days it will provide up to 384 kilobits. So the changes are going to be
诲谤补尘补迟颈肠.鈥�
Several engineering challenges need to be overcome before 3G becomes a
reality. One of the biggest is maintaining an always-on Internet connection
while you are on the move, and keeping it live as you move from one base station
cell to another. This switch-over, called the 鈥渉and-off鈥�, is far from perfect on
today鈥檚 networks.
The GSM network measures the strength of a phone鈥檚 signal received at every
nearby base station, and locks on to the strongest. But as anyone who鈥檚 used a
mobile in a car or train knows all too well, calls have a habit of dropping out
in mid-sentence when the link is lost.
To minimise the chance of this happening to always-on links, 3G networks will
adopt standards such as the Universal Mobile Telecommunications System. This
uses a trick called soft hand-off. 鈥淚f a 3G mobile detects two good base
stations, it sets up connections to both of them at once,鈥� says Uddenfeldt. This
makes it much less likely you will lose the call, and means signal quality
should improve as well, because the network can always listen to the best
available station.
The 3G development teams are also collaborating to re-engineer the data
packets the networks will carry. One problem is the Internet packet
header鈥攖he 鈥渆nvelope鈥� on which are written the source and destination
addresses. On the Net, more than half of every packet is devoted to this kind of
information. 鈥淭hat鈥檚 a tremendous waste of network resources,鈥� says Eriksson. It
effectively halves the network鈥檚 capacity. Today, it takes 40 bytes of header to
carry 33 bytes of data. In 3G networks, compression will bring this down to just
3 bytes of header.
It won鈥檛 just be the network that will benefit from new ideas. The 3G mobiles
themselves will be packed with ultrafast signal processors to handle the
expected new applications, like streaming video. Says Uddenfeldt: 鈥淚t will be
great for watching news flashes or soccer highlights, and a lot of kids would
love to be able to store all their music somewhere and stream it online.鈥� At the
promised 2 megabits a second, it should also be possible to stream video from a
3G camcorder back to your video recorder at home, perhaps making tiny tapeless
camcorders a reality. Ericsson is even thinking ahead to when it will enhance 3G
to 8 megabits a second, anticipating the arrival of 4G.
鈥淧eople are going to stop carrying around things like laptops,鈥� Uddenfeldt
predicts. 鈥淢ore and more devices are going to fit in your pocket. People will
discover that their mobile can handle video, work like a Palm Pilot and be a
phone. It鈥檚 much more powerful than what they have at home.鈥�
And what will we call these new non-phones? 鈥淲e鈥檙e calling them
communicators,鈥� says Uddenfeldt. James T. Kirk would have been proud. Next stop,
presumably, the tricorder.
