WiMax: Wrong For Urban Areas?

By Alex Goldman

June 15, 2004

In a controversial keynote at the Wi-Fi Planet Conference, an industry CEO said WiMax would be inappropriate for dense urban areas. He proposes a different architecture.

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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