New transmission technology promises a powerful revolution in radio signal strength.
- From: Grappler <grappler@xxxxxxxxxxxx>
- Date: Thu, 10 Nov 2005 22:22:33 +0000
>From Guardian Online
New transmission technology promises a powerful revolution in radio
signal strength
I'm standing at the bottom of a radio tower in the Everglades. The top
of the tower, 850ft above me, seems to sway in the clouds. All around
are trees, ravaged and felled by hurricanes. No one sensible would go
up that tower, but I want to, because I have just been told that up
there, the limits of radio transmission technology are about to be
broken.
At the top, we are told, is a radio transmitter no stronger than the
base station of a cordless phone. Normally, its signals would struggle
to reach me at the tower's base. But we are about to drive 18 miles,
and pick up those signals, as clear as a bell.
This all happened last Thursday, when a company called xG Technology
(www.xgtechnology.com) took the wraps off a new radio scheme, showing
it to three UK journalists and a bunch of investors. We are all asking
ourselves the same question: is this for real?
xG says that xMax is a thousand times more efficient than other
wireless systems, including current mobile phone systems, and even
those still to be widely implemented, such as WiMax.
The transmitter in the 900MHz band used in some cordless phones is
only using 50mW of power. Both the transmitter and the receiver
antennae have fairly high gain, but not enough to boost it that far -
especially as this is not a focused beam. A radio enthusiast with a
Pringles tube can coax a Wi-Fi signal a few miles, but this is
broadcasting in every direction at once.
Under those conditions, any conventional signal would be impossible to
pick up at 18 miles. And yet we saw a 3.7Mbps data stream, enough to
send video with sound. If this is real, it is very new.
xMax uses something called single-cycle modulation. Most radio systems
use a carrier signal, and alter it to send data. The transmitter
changes the amplitude, the frequency or the phase of the carrier, and
the receiver locks on to the signal, and detects those changes.
Normally, it takes several oscillations of the carrier to send one bit
of data, but xMax changes each wave cycle individually. "While other
modulation schemes take a thousand cycles to send one bit, we can send
a bit in a single cycle," says Joe Bobier, the inventor
(http://tinyurl.com/a5jx7). The technology also operates on many
frequencies simultaneously.
That means xMax needs much less power to send data. One xMax base
station can cover an area that would take 90 WiMax transmitters, and
would cost a fraction of the price, says Bobier.
A lot depends on the receiver, which Bobier says is clever, but simple
to build: it's just a "50-cent circuit", he says, but it synchronises
closely with the transmitter and somehow manages to filter out much
louder conventional radio signals.
At the demonstration, the receiving equipment was, literally, a black
box, hooked up to an antenna and an oscilloscope that showed the
signal was being received. Bobier wouldn't describe it in detail until
his patent is issued, next month.
Bobier has convinced one scientist: "xMax is unconventional," says
Stuart Schwartz, professor of electrical engineering at Princeton
University, and one outsider to get a full explanation. "It is clever
and innovative, but it is not magic."
According to Schwartz, the xMax modulation scheme could be used on any
radio system. It would allow a home wireless Lan using nanoWatts of
power (a few billionths of current levels), so devices could run for a
year on small batteries. It could even be used on signals travelling
on copper wire, making everyone's broadband go further at much faster
data rates.
"What Joe built is so broad, we had to focus on one thing," said Rick
Mooers, head of Mooers Branton, the bank that is backing xMax, and
also xG's chief executive. "The demo we've seen is purpose-built to
show xMax as a powerful alternative to the two hottest wireless
technologies around: 3G cellular services and the WiMax wireless
broadband technology."
It's also, we suspect, designed to persuade the companies behind those
technologies to buy into xG. "We're in discussion with channel
partners, to make a shrinkwrapped package that would allow anyone to
set up as a wireless service provider," says Mooers.
But before that happens, someone will have to give this a more
detailed check. The UK journalists tested the system as well as we
could. Rupert Goodwins, of ZDNet (http://tinyurl.com/7ed7x), tested
the connections on the receiver, and agreed the signal was coming from
outside. Adrian Mars, researching future radio technologies for the
Cambridge-MIT Institute, checked xG's distance claims against his own
global positioning system receiver. But none of us got to go up the
tower. Schwartz has seen the transmitter and he's convinced. If xG is
going to revolutionise radio, someone is going to have to go up and
take a look at it.
.
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