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Hearing Multiple Signals

MIMO, the new wireless technology, promises faster and more powerful Wi-Fi. But just how well does it work?

Anyone who uses wireless anything – a Wi-Fi network at a hotel, cellular phones, BlackBerries – knows some of the problems with the technology: Wireless networks transmit data much more slowly than most wired ones, they don’t always work, and they have a maddening tendency to disconnect without warning. There’s a constant worry of being out of range or having a bad connection.

Still, each new generation of wireless gadgets gets better, generally cheaper, and seemingly more popular. Now an emerging wireless networking technology called MIMO promises real breakthroughs in speed, accessibility, and reliability. That has implications for today’s corporate networks, home Wi-Fi networks, and cellular networks.

MIMO stands for “multiple input, multiple output.” Wi-Fi routers based on the technology use a series of radios in conjunction with several “smart” antennas to send and receive signals simultaneously. Handling multiple signals makes possible much stronger, more reliable, and faster transmissions – in theory.

Consumers will see MIMO in a new class of wireless networking products categorized as “pre-n,” after the nomenclature of the Institute of Electrical and Electronics Engineers’ 802.11 wireless Ethernet standards committee. The IEEE wireless standards with the broadest impact have been, in the order in which they reached market, 802.11b, 802.11a, and 802.11g.

There is not yet an 802.11n, but the consumer market for pre-n products is already flourishing. One of the leading manufacturers, Airgo Networks, a Palo Alto, CA, startup, has already sold more than four million MIMO chipsets, which appear in wireless networking routers and adaptors from LinkSys, Belkin, and other vendors.

Indeed, while MIMO has not yet become a Wi-Fi standard, routers and PC cards based on it are easy to find, both online and in stores. Samsung has even put MIMO on the motherboards of two of its notebook computer models selling in Asia and Europe (most U.S. electronics companies are expected to wait until the IEEE approves its standard before integrating MIMO into their systems). Meanwhile, Orthogon Systems, a British startup, has begun offering networking equipment aimed at long-range networks that uses a method similar to MIMO.

To see how well MIMO actually works, I bought a Belkin router that uses the Airgo chipset. The router is equipped with three radios and three antennas, which are intended to increase its range, reliability, and speed. In fact, Belkin claims an 800 percent improvement in coverage area over the best of current Wi-Fi routers and a 600 percent improvement in speed.

I had not previously set up a wireless router. And since my technical skills mostly involve breaking things in ways their makers had not imagined, I expected a challenge. I popped the installation CD into my notebook’s drive and followed the instructions. When it came time, I plugged in the router, which boasted four Ethernet ports to connect to PCs, one port for the modem, and a plug for a power cord on one end and three nubby antennas sticking out of the other. Windows XP Home Edition, which I use, protested that I was installing an unknown device that could destabilize my system. Nevertheless, I pressed on.

To get Internet access, I ran a cable from my DSL modem to the router, which sits in my basement office, and then another cable from the router to my notebook computer. That worked fine. But when I installed the MIMO notebook card and pulled the cable, I lost my connection. It took a bit of poking around in the software that comes with the system to realize I needed to tell it to activate. (Okay, so the truth is, I was on the phone interviewing someone for this story and complained about the lost connection. He asked me whether the radio was on. One right-click of the mouse later, it was.)

Including the basement, our house is about 3,000 square feet, but even in the farthest point from the MIMO router, I have no connectivity problems and no drop-off in download speeds. In fact, Belkin claims good connectivity over 250,000 square feet (the fastest current version of Wi-Fi, 802.11g, generally covers less than one-fifth that), so I could probably read e-mail while mowing my lawn, if I felt like it. And the MIMO notebook card works fine in the local coffee shop, using the existing Wi-Fi standard.

In short, MIMO looks to be a good thing for people and businesses whose connectivity is spotty and unreliable or who experience slow data transmission for PCs at the extreme ends of their current Wi-Fi networks’ reach. That’s nice, but the importance of MIMO goes far beyond improving the performance of Wi-Fi. It is, in fact, “the most significant radio technology ever,” claims wireless consultant Craig Mathias, principal at the Farpoint Group in Ashland, MA. The reason for such excitement is that MIMO appears to be an excellent answer to a wireless problem that’s existed since Marconi.

“In wireless communication, the biggest problem has always been multipath interference – signals taking different paths and canceling each other out or blurring the signal,” explains Ira Brodsky, president of Datacomm Research in St. Louis. The result of this interference is familiar to anyone who’s ever had trouble tuning in a station over a car radio: signal drops – the very thing wireless networks must be engineered to prevent.

MIMO is designed to turn this inherent problem with wireless into an advantage. In a sense, MIMO is to wireless what multiprocessing is to computing – a way to move data faster by sending it through multiple channels. Each of the radios on the MIMO chipset pulls in a signal, and all the signals are then run through digital signal-processing algorithms and re-formed into a single transmission. This use of redundant multiple signals allows MIMO to increase the reliability and range of transmissions. Indeed, the strategy is widely applicable, and over the next several years, MIMO technology may make its way into cellular networks and products that might benefit from wireless transmission, like camcorders and televisions.

The exact origins of today’s MIMO technology are disputed, which seems fitting, since there is no agreement on its exact definition, either. There are various versions of the technology with such esoteric names as “spatial diversity multiplexing,” “beamforming,” “antenna diversity,” and “channel beaming.” What is clear is that Airgo, headed by CEO Greg Raleigh, who as a graduate student at Stanford University in the 1990s helped pioneer MIMO, is the first company to come up with a version cheap enough to make it onto the consumer market.

Adding to the confusion around MIMO is that it is to be the basis for the IEEE’s 802.11n standard, which is not yet a standard and is not expected to become one until at least 2007.

The bottom line for consumers? People who buy MIMO products before 2007 will eventually have to buy new products to get the full speed advantages of the technique when the standard has finally been finished, predicts Robert W. Heath, an assistant professor in electrical and computer engineering at the University of Texas at Austin. Still, if MIMO keeps improving, it might be well worth it.

A wireless network’s performance isn’t based on just one factor, of course: my router can’t download data from the Web any faster than my DSL connection allows. Network speed is measured in megabits, or millions of bits, per second, and my DSL on a good day hits two megabits a second. My router’s claimed top speed is 108 megabits a second. So though I knew the MIMO router wouldn’t let my laptop access the Internet any faster, I did hope that I could use it to enhance my house’s feeble wireless capabilities.

Having noticed new televisions with built-in Wi-Fi, I imagined using MIMO to zip downloads from digital video cameras to the TV, or even to take stuff from the digital video recorder and zap it to one of our other TVs. In fact, I was letting my imagination run amok, warns Mathias. MIMO isn’t yet fast enough to handle large amounts of video.

And MIMO won’t be a universal solution. In some kinds of wireless networks, such as sensor or radio frequency ID networks, single radios will always be adequate – and cheaper. But for anything that involves data or voice, MIMO is likely to be adopted. For those uses, speed of data transfer is important. And MIMO looks like the technology that will finally let wireless networks start to close the gap between their speed and reliability and those of wired networks.

Wireless Wonders
Belkin Wireless Pre-N Router ($150)
Wireless Pre-N Notebook Network Card ($100)

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