WiMax: Wrong For Urban Areas?

Bernard Herscovich, President and CEO of Reston, Va.-based BelAir Networks, said that the traditional wireless Internet architecture will eliminate all of the advantages of WiMax in urban settings.


Herscovich described the standard outdoor wireless Internet architecture as
the “big stick” approach: find a tall tower or pole, and put your antenna on it.

This approach works in rural areas. WISPs across North America and around the
world are excited about the possibilities that WiMax offers: longer range and
lower CPE costs would reduce expenses at both ends, with fewer APs serving more
customers at a lower up front cost.

But these cost savings would be impossible in urban areas. The urban
environment is unique, Herscovich noted. “Tall buildings block signals, and
create lots of shadows. The service competes with cable and DSL, and it has to
offer something they cannot. It can compete by offering mobility.”

Celling wireless service

But to offer mobility,
the wireless service must be as pervasive as cell phone service.

The answer, Herscovich said, was to create small cells instead of trying to
cover large areas with a single antenna. He did some basic math to prove the
point:


Let’s say, to simplify things, that WiMax enables a 10 mile radius of
coverage. If you’re using a sectorized antenna, each antenna covers 1/4 of the
area (or 1/6 with some systems). So the number of square miles covered by an the
access point is pi times the radius squared, or approximately 3.14 x
102, or 314 miles. Each antenna covers 1/4 of that, or 78.5 square
miles. Even with 100 Mbps of bandwidth per sector (which may or may not be
attained outside the lab), that leaves a little in any square mile.>/p>

But drop the coverage radius to a half mile, and the equation changes
completely. 3.14 x 0.52 = 0.785 square miles. Each sector is 1/4 of
that, or about 1/5 of a square mile.


So you need smaller cells.

Combine this with a mesh architecture, and you can abandon the big stick,
drop the antennas down into the urban canyon, and use LOS for short hops between
the APs. You’re no longer relying on a reflected signal, so signal quality
increases.

But would it work in real life? A group of vendors not affiliated with BelAir
were at the conference, showing that it could be done. The group that wired the
city of Cerritos, Calif. had just announced the unwiring of another city,
Chaska, Minn., on May 25. Representatives from Woodland Hills, Calif.-based ISP
Aiirmesh
Communications
and equipment makers Tropos Networks (based in Sunnyvale,
Calif.) and Pronto Networks (based in Pleasanton,
Calif.) spoke in a separate session
covering the Cerritos mesh deployment
.

For urban ISPs, Herscovich noted, “the cellular LAN architecture takes Wi-Fi
downtown.” In most cases, urban ISPs will use Wi-Fi to create hotzones of
connectivity. Such ISPs might, Herscovich conceded, use WiMax to serve massive
amounts of bandwidth to valuable large enterprise customers, but hotzones will
not require Wi-Max.

Phil Belanger, BelAir vice president of marketing, told us that at the moment
BelAir is having its greatest success in serving the hospitality industry (i.e.,
hotels). The company is selling slimmer two radio versions of its standard four
radio unit at a cheaper price to complete a local mesh architecture that can
reach upward, providing access in the hotel lobby and to hotel rooms. Mesh Wi-Fi
is especially effective in hotels that have an open atrium through which the
signal can travel directly to every hotel room.

Whatever the scale of the deployment, it seems that Wi-Fi and the mesh
architecture will be there, from smaller deployments serving individual tall
buildings to larger deployments covering entire cities.

WiMax will play a role, but Wi-Fi’s advantages will tell: Wi-Fi is cheaper
and equipment is easy to acquire. But, Herscovich noted, the primary
consideration for deployers of hotzones may be that almost everybody will have a
Wi-Fi client in the near future, whether they have an embedded client in their
Intel Centrino laptop or use a Wi-Fi card.

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