http://www.newscientist.com/news/news.jsp?id=ns99991593
"Mesh radio" can deliver super-fast internet for all 19:00 21 November 01
Barry Fox
A new type of high-capacity wireless network called mesh radio will get its
first users early in 2002 - a hundred lucky households in Cardiff, Wales.
>>It will let them watch movies on demand, hold broadcast-quality video chats
with
their neighbours, and download from the internet at a blistering four
megabits
per second - many times the speed of wired broadband delivery systems like
ADSL
and cable modems.
Even better, says its developers, mesh radio will not 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 "wireless cable" networks,
they
are often used in rural areas in the US where it's 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
"see" only one-third of the homes in its area.
Mini base station
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 - or master node - connects 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 - in the millimetre waveband. Later systems
will
work at 40 gigahertz. Two-way data rates of four megabits per second are said
to
be possible for up to 600 subscribers per square kilometre.
Health effects
The mesh radio idea has been developed and patented by Cambridge company
Radiant Networks, but it is a conventional telecoms company, BT, that's
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 one watt, whereas
cellphone masts push out eight watts...<<
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