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Interference and Bandwidth

Whenever I talk to advocates of 802.11a, they inevitably point out that the 2.4-GHz spectrum is home to many technologies, making the risk of interference a serious concern. They're right, to a degree, but their solution is merely a quick fix. It's no surprise that some congestion will accompany market success with any unlicensed wireless technology. But interference often can be managed effectively. If 5-GHz technology proves as successful as 2.4 GHz, we'll have problems in those bands as well. While you may get some temporary relief by moving to a less popular band, the benefit is often short-lived, and the costs can be quite high.

So exactly what are the costs associated with moving to 5 GHz? The most obvious is simply the price of the products. The volumes we're seeing in the 802.11b WiFi (Wireless Fidelity) market make it easier for vendors to accept smaller margins. And the competition between Intersil Corp., Agere Systems and Asian producers is just enough to ensure continued competition on price. 802.11b chipsets now cost about $35 in quantity. In the 11a market, vendors will need to accept lower margins from the start or else hope that users will pay more for "premium" features such as higher speed.

There's no debating that 11a products will offer higher speed. Even at 60 percent efficiency, getting 30 Mbps of throughput out of 54-Mbps products will enable new bandwidth-intensive applications. However, this added performance comes at a cost: Range will be reduced. The laws of physics that control wave propagation will not be suspended anytime soon, so 5-GHz products will require smaller cell sizes than their 2.4-GHz cousins. Improved modulation schemes may provide 5-GHz products with a range equivalent to 11b systems at equal performance levels. I've seen conflicting reports on this topic, but the bottom line is we won't know the truth until products ship.

If you're expecting the maximum speed of 54 Mbps, be prepared for tiny cell sizes and higher build-out costs for access-point infrastructure. That's why dual-slot access points don't provide a truly effective migration path from 11b to 11a. However, minimizing cell size reduces user density, which improves performance. Even WiFi vendors have recognized this point, and some now allow power levels on access points to be reduced to limit cell size.

The uncertain future of wireless probably has you scratching your head, and there's still one more variable to consider. In 2002, you may see 2.4-GHz products breaking the 20-Mbps barrier. As I write this, there is ambiguity regarding standards, and a fair amount of vendor politicking is taking place in standards committees. But you can bet on one thing: Products will be available next year. So what are the real questions? Will those products be affordable, and will they maintain backward compatibility? Stay tuned.