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Wi-Fi: Pumping Up The Volume


In radio's early days, engineers learned that signals bounce off obstacles between the transmitter and the receiver and often arrive at the target antenna via multiple paths. Because these paths vary in length, the waves arrive slightly out of sync. The resulting babble of overlapping signals can confuse the receiver. But this curse has now been turned into a benefit that can extend the range of your Wi-Fi network.

The secret is the amazing processing power that can now be built cheaply into almost any gizmo. For a century, radios have been designed to reject so-called multipath signals. New smart antennas and microprocessor-enhanced radios can combine the out-of-sync radio waves to create a single, much stronger signal. The result, in products now hitting the market, is souped-up Wi-Fi gear that lets a single router or other "access point" provide wireless coverage throughout the home, including spots that normally get poor coverage or none.

The new technology is called MIMO, short for its less sonorous technical name: multiple in, multiple out. MIMO is going to be part of a new extended-range specification for wireless networks, known as 802.11n in the Wi-Fi alphabet soup. While formal approval of this standard is still two years off, gearmakers are already bringing preliminary products to market. To get the maximum range, you have to pair one of them with a receiver of the same brand. But even older Wi-Fi devices that don't use MIMO will stay connected at greater distances when used with one of these new routers.

I TRIED OUT TWO MIMO ACCESS POINTS, a Linksys Wireless-G Broadband Router with SRX (around $200) and a Netgear RangeMax Wireless Router (around $130), which take different approaches. The Linksys uses technology from Airgo Networks -- also found in products from Belkin and Buffalo Technology -- that employs three vertical antennas to create a more robust signal. The Netgear relies on an array of seven antennas to create a focused beam that it aims at the receiver -- a concept also used in some radar systems.

Linksys claims triple the range of a standard access point, while Netgear boasts of a "1,000% increase in coverage." By themselves, these claims are as meaningless as the 100-foot range you're supposed to get with standard Wi-Fi. Tests are done under ideal conditions that have little bearing on the real world, where signals have to get through walls or between floors.

Whatever the claims, however, both of these new access points proved to be splendid performers when I placed a matching PC card adapter in my laptop. They maintained good signal strength even with considerable distance and several walls between the access point and the laptop. Of course, if you already have a Wi-Fi laptop, it's annoying to cough up an extra $100 or so for an adapter that's clumsier than the built-in wireless. And on some devices, such as Wi-Fi Pocket PCs, you don't have the option of using a PC card.

The good news is that the MIMO access points are not only compatible with existing Wi-Fi receivers (802.11b or g) but they also extend the range even when talking to these older devices. I tested such an arrangement using signal-measuring software and found that the signal from the new Linksys and Netgear access points at the edge of normal Wi-Fi range was about twice as strong as with a conventional Linksys access point. That's enough to make the difference between a slow, marginal connection and a fast, solid one.

There's one disadvantage to extended range: The signal is far more likely to reach well outside your home or office. This means you should take care to secure your network. Following the instructions in your manual, make sure, at a minimum, that Wired Equivalent Privacy (WEP) is turned on, and if all of the devices on your network support it, go for the stronger Wi-Fi Protected Access (WPA). Also ensure that each computer has firewall software running. Otherwise you may find yourself providing access to your Internet connection, and maybe your data, to the whole neighborhood.

For a collection of past columns and online-only reviews of technology products, click here

By Stephen H. Wildstrom


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