As
a youth reading about the history of radio propagation, I always liked the idea
of the “ether”. It was
comforting to imagine that there was some mysterious substance throughout space
that supported radio wave propagation. I
would watch the water ripple when I threw a rock into a pond, and I would have
some understanding of how it must be with this substance they called the ether.
I had a hard time getting used to the fact that radio signals propagate
through empty space. What a miracle
it is that we can speak and send signals through nothingness!
As
I write, I’m looking out a window at the blue sky above and thinking about
what a lot of empty space there is. Surely
there is enough for everyone. I
sometimes imagine how Marconi must have felt when his coherer detected the first
pulses from the spark transmitter across the hill.
The possibilities were infinite; a whole new universe had been opened for
mankind.
Immediately
following Marconi’s experiments there was a decade at the beginning of the
last century when any amateur could build a spark transmitter and get on the
air, blasting radiation across the whole radio frequency band.
In 1911 there were an estimated 10,000 radio amateurs in the country and
thousands of stations on the air. But
the end of that radio anarchy was precipitated the night of April 14th,
1912 when the Titanic sunk. Hundreds
of lives were saved because the sister ship Carpathia received the radioed SOS
from the sinking Titanic. On the
other hand, hundreds of lives were lost because the radio operator in the
nearest ship, the Californian, had gone to bed.
Within a month, a bill was introduced into the US Congress to regulate
the use of the radio frequency spectrum. Maybe,
after all, there wasn’t enough for everyone.
Now
I’m still looking at that blue sky above and thinking how full it must be of
radio waves. If we could see those
waves, like some kind of laser show, then the sky would be brilliantly lit with
a rainbow of bright colors. It
seems as if in that vastness of space there is almost no capacity left, and what
little there is has become extraordinarily precious.
Last
year when the European nations auctioned off the spectrum for the third
generation wireless (3G) spectrum, the auctions brought about $190B.
The governments exulted in having raised such incredible amounts, but the
carriers who bid these prices were saddled with huge debts.
In the UK the companies who bought the 3G spectrum paid enough money to
have put a fiber into every home in the country
-- and all they got was the right to use this spectrum.
Which would you rather have – a broadband fiber into your home or a tax
on the use of wireless devices? Such
was the bizarre consequence of the auction rules, the 3G hype, and the market
bubble that preceded the auctions.
Meanwhile,
engineers have been designing more efficient methods for the wireless
transmission of information. New
algorithms for signal processing and the inevitable progress in electronics
dictated by Moore’s Law have opened up the possibility of orders of magnitude
improvement in efficiency. Some
people are even saying that the wireless capacity is actually infinite, and that
there is no reason for regulation at all.
Among
the new technologies are adaptive antennas and the concept of space-to-space
transmission, where only a narrow corridor of that empty space is occupied.
Then there is the array processing of multipath signals, where all of the
echoes of all the signals present are collected and optimally disentangled in
space and time. Another technique
uses successive interference cancellation, detecting and then subtracting out
potentially interfering signals.
While
all of these signal processing algorithms promise much greater utilization of
the radio spectrum, probably the most revolutionary concept is packet relay, in
which each wireless device cooperatively forwards packets received from its
neighbors toward their intended destinations.
Much research has been done on these so-called ad hoc networks.
Interestingly, such networks scale to infinite capacity; as the density
of devices increases, each device lowers its transmitted power accordingly.
While 3G moves ponderously forward, a quiet revolution is happening
around IEEE 802.11, the wireless packet standard.
But
all this technology is theory, not practice.
In practice the spectrum is full of legacy devices, blasting energy in
the old ways over spectrum bought and owned by watchful tenants.
After paying billions for the right to use a small slice of spectrum,
owners are unlikely to embrace new invaders with non-standard formats.
The problem with spectrum is that we gave most of it away and then sold
the rest.
So
is wireless capacity extremely limited and expensive, or is it infinite and
free? And how do we get from here
to there?
Robert
W. Lucky