EARLY next year, a hundred lucky households in Cardiff will get a free
glimpse of the future. They will be the first in the world to plug into a new
type of high-capacity wireless network called mesh radio. It will let them watch
movies on demand, hold broadcast-quality video chats with their neighbours, and
download from the Internet at a blistering 4 megabits per second鈥攎any
times the speed of wired broadband delivery systems like ADSL and cable
modems.
Even better, says its developers, mesh radio won鈥檛 slow down when a lot of
people try to use it at the same time. Home ADSL services typically provide a
maximum data rate of 500 kilobits per second, but the bandwidth available to a
user is much lower if several people in the street are online at the same time.
Cable modems are similar.
Conventional wireless data systems, known as multipoint video distribution
services (MVDS) networks, use a powerful base station with a tall antenna to
broadcast to homes over a wide area. Also dubbed 鈥渨ireless cable鈥� networks, they
are often used in rural areas in the US where it鈥檚 uneconomic to lay cable. But
any tall buildings in the way, or even a tree, absorbs the signals, creating
blind spots where homes cannot communicate. As a result, a base station may
鈥渟ee鈥� only one-third of the homes in its area.
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Mesh radio achieves nearly 100 per cent cover by turning each home into a
mini base station. A stubby unit on the roof, hides four directional antennas
with motors that automatically align them with other antennas on other houses.
This allows each node to communicate with several others at the same time. If
contact is lost, it can automatically readjust its antenna to point to a
different one.
A network control centre鈥攐r master node鈥攃onnects to an
optical-fibre trunk line connected to video and Internet resources. The data
flowing round the network is labelled so that each home has its own private,
indirect connection to the trunk. The system on trial in Cardiff, and further
trials planned for the US, Spain and Germany, works at 28 gigahertz鈥攊n the
millimetre waveband. Later systems will work at 40 gigahertz. Two-way data rates
of 4 megabits per second are said to be possible for up to 600 subscribers per
square kilometre.
The mesh radio idea has been developed and patented by Cambridge company
Radiant Networks, but it鈥檚 a conventional telecoms company, BT, that鈥檚 running
the Cardiff consumer trial. BT already runs an ADSL service, and wants to see if
the mesh idea works as well as Radiant predicts.
Compared with cellphones, mesh technology may raise fewer concerns over
radiation health effects. It operates at higher frequencies than the microwaves
used by cellphone networks, allowing the signals to travel high in the air in a
tight line-of-sight beam. Power levels will be less than 1 watt鈥攚hereas
cellphone masts push out 8 watts.
But the World Health Organization is reserving judgement. It recently
rebutted reports in the Australian press that it had declared mobile phones and
base stations to be safe. Not so, says the WHO: 鈥淭here are gaps in knowledge
which need three to four years of research.鈥� The WHO was unaware of mesh radio
and Britain鈥檚 other 28 gigahertz trials, and has now asked for full technical
details on the systems.
