[IP] Re: ur comments appreciated: Beyond White Spaces

[David Farber <dave@farber.net>]

Begin forwarded message:

From: Lars Poulsen <lpoulsen@afar.net>
Date: October 27, 2008 12:06:27 PM EDT
To: dave@farber.net
Subject: Re: [IP] WORTH READING  ur comments appreciated: Beyond White  
Spaces

> From: "David P. Reed" <dpreed@reed.com>
> Date: October 27, 2008 9:57:47 AM EDT
> To: dave@farber.net
> Cc: ip <ip@v2.listbox.com>, Brett Glass <nnsquad@brettglass.com>
> Subject: Re: [IP] Re:   Your comments appreciated: Beyond White Spaces
>
> ...  Not that the other side conveys the physics correctly, either.   
> Here's the real scoop:
Like everything else in engineering, choice of spectrum is a matter of  
trade-offs.
As someone who works in equipment design, mostly for unlicensed  
applications,
I have spent 10 years slowly gaining an appreciation of which bands  
are good
for what. It is very hard to untangle which properties of various  
bands are
created by physics, and which by culture, licensing and engineering  
traditions.

Short wavelengths are more strictly line-of-sight, longer wavelengths  
(lower
frequencies) tend to "flow" around minor obstacles. Higher frequencies  
are
attenuated more by fog, rain, leaves and other diffuse obstructions.
Shorter wavelengths are easier to focus (i.e. same size antenna is  
more wave-
lengths, and thus more dB of antenna gain).

Higher frequencies can be modulated with more bits per second, and  
additionally,
you tend to get allotted a wider channel at higher frequencies. But  
signals
with a higher modulation require better S/N ratio to demodulate. To  
improve
S/N ratio at the same signal strength, one needs more antenna gain (more
sharply focused beam) requiring better aiming of the antennas (and a  
more rigid
antenna mast).

The result of these factors has been that the abundant spectrum  
available
above 26GHz is not much used. 2-3GHz in many ways is a "sweet spot".
5-6GHz is more challenging to deploy, and not very useful for mobility
applications where antenna gain is not practical on the mobile end of  
the
link.

It seems to me that the unlicensed bands at 2.4 and 5.x have been a  
great
public good. In urban areas, however, outdoor use of these is  
challenging
because of overuse. It would be useful to have 500 MHz available under a
"light licensing" scheme, where users would be required to register and
reserve a modest slice (10-20 MHz per user) for a couple of years at a  
time,
with auctions to resolve contention if and where contention arises, but
with free use in areas of no contention. In the current debate, I hear
lots of players wanting "free access" which I think prevents many  
valuable
services from viability. I agree that current (US) licensing schemes are
unwieldy, but I would prefer to see the system improved, rather than
thrown out.

/ Lars Poulsen
Afar Communications Inc





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