more on WiMax

[David Farber <dave () farber net>]

------ Forwarded Message
From: Brett Glass <brett () lariat org>
Date: Tue, 08 Feb 2005 11:20:57 -0700
To: <dave () farber net>, Ip <ip () v2 listbox com>
Subject: Re: [IP] WiMax

[Dave: This is slightly long-winded, but it's important; please post. -BG]

As an actively operating WISP, I'd like to chime in on this thread.

There's nothing that special about WiMAX. It incorporates technological
elements of other systems that are as old as 5 years -- nothing novel
about it. And there are plenty of technologies now that can do similar
things. Even 2.4 GHz Wi-Fi (with the settings adjusted for greater
distances) is quite usable to deliver wireless broadband. (I do it.)
And at least one manufacturer is now rolling out outdoor point-to-multipoint
equipment for the 5.8 GHz band based on -- you guessed it -- 802.11a.
It works and works well.

WiMax won't help with interference problems; providers will still
bump into one another on the unlicensed spectrum as they did before.
And it won't vastly increase range or efficiency. Some current systems
are already approaching the theoretical maximum, especially in noisy
environments.

The only potential benefit of WiMax -- and I DO mean its one and only
advantage -- is its potential to reduce equipment costs. Because many
radio manufacturers will able to use the same chipsets, and the use of
the same standard by many vendors will make equipment interoperable and
interchangeable, we can expect to see economies of scale that will bring
the cost of a non-Wi-Fi broadband radio down to a level that customers are
willing to pay. (Currently, the single biggest obstacle we face when
trying to persuade potential customers to hook up is the cost of the radio.)
The benefit will be limited, however, because FCC-approved Wi-Fi radios --
at least ones that will work well if the user is half a mile or less
from the access point -- can already be had for between $100 and $200.

Thus, WiMax is a "solution" to a problem which is relatively minor compared
to the others faced by wireless broadband -- the biggest being the lack of
dedicated spectrum and appropriate rules governing how it should be used.
WiMAX is thus, in many ways, a mere rearrangement of the deck chairs on the
proverbial Titanic.

While WiMAX will be a welcome option, the things that are needed to make
wireless broadband a truly practical option for consumers are as follows.

* Dedicated unlicensed spectrum. Currently, wireless broadband systems share
the unlicensed bands with devices ranging from cordless phones to baby
monitors. Consumers do not realize that -- because the wireless devices they
use are allowed to emit as much power on the same frequencies as wireless
broadband devices -- they can take down their own broadband connections, or
those of their neighbors, by innocently purchasing and using a perfectly
good,
FCC-approved household device. And they cannot be expected to be able to
identify 
devices might interfere. (We have one client whose Internet connection died
when
his teenage daughter went out on the porch with a cordless phone -- directly
in
front of the antenna.) Because many customers may ultimately use wireless
broadband
as their way of obtaining essential telephone service as well as Internet,
we cannot
allow consumer devices to interfere with wireless broadband at random, or to
raise
the noise floor to the point where it is unreliable. The FCC is now
considering
a rulemaking to open up spectrum in the 3.6 GHz range to unlicensed use.
Just as
some unlicensed frequencies are dedicated for other purposes (cf Part 15),
these 
should be dedicated for outdoor wireless broadband.

* Mandatory spectral efficiency. Currently, manufacturers make their radio
systems
more robust -- and thus more likely to be the "last system standing" in a
noisy
environment -- by reducing their spectral efficiency. (Motorola's Canopy
system
is a good example; it uses the least efficient modulation schemes to blast
through
a crowded band, ruining it for others while at the same time failing to use
it
efficiently.) To avoid a "race to the bottom" in which vendors make their
systems
slower and less efficient to obtain more energy per bit (and, hence, drown
out
other systems), the FCC should include in the rules for new unlicensed bands
a
requirement that all equipment use a modulation scheme with spectral
efficiency
at least equal to that of 16-level QAM (quadrature/amplitude modulation). No
specific technology should be mandated, but a minimum spectral efficiency
should.

* Power limits should be set so as to allow a professionally installed
wireless
broadband access point to have a usable range of 10 or more miles in the
presence
of heavy precipitation. The current FCC limits, together with local
restrictions
on the placement of towers, often make it impractical to serve all users
within
a geographic area. 

* Some amount of unlicensed spectrum should be reserved for outdoor
point-to-point 
links only. The reason for this is that wireless broadband access points
often require
"backhauls" -- links back to the Internet -- which are also wireless. (In
fact,
such links will increasinglly become a necessity as the Bells are allowed to
evict
competitors from their lines.) Interference among point-to-point links is
rare,
and antennas can be aimed to overcome it. But a point-to-multipoint system
can generate
strong interference that may come from any direction at any time (for
example, if
a new subscriber on one system appears next to a radio tower used by a
different one). 
Thus, to ensure the reliability of backhauls (which, if interrupted, could
knock out 
Internet telephone service to hundreds of subscribers), separate spectrum
should be 
available for them.

* Because omnidirectional antennas make it more economical to erect access
points 
and make it possible to serve a wider area with less spectrum, the rules for
new 
unlicensed bands should not impose a penalty on their use in
point-to-multipoint
systems (as they effectively do now). However, the rules should require the
use of 
antennas with narrow beamwidths (no more than 15 degrees) at subscriber
sites
to avoid interfering with other systems in the vicinity.

* The rules should also limit the density of access points deployed by any
one
provider, so as to prevent monopolization of the band a la Metricom.
(Metricom's
Ricochet system deployed thousands of access points atop street lights,
effectively
smothering the 900 MHz spectrum on which it operated and making that band
unusable
by anyone else for most outdoor applications.)

In summary: If WiMAX helps a small bit by making equipment less expensive,
so much 
the better. However, the biggest hurdles faced by wireless broadband involve
not 
equipment standards but sensible oversight of, and appropriate use of, the
radio
spectrum. Hopefully, the FCC -- now under new leadership -- will meet this
challenge.

--Brett Glass


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