Wow, what a year. Camera phones. Local-number portability. 802.11g. More spectrum for both licensed and unlicensed use. WLAN prices falling through the floor. Centrino.

But this being an engineering publication, I feel compelled to recognize one technology as having the farthest-reaching influence over our little corner of the electronics world. The award goes to MIMO-multiple input, multiple output.

What's being input and output is the radio channel itself. MIMO adds a third spatial dimension beyond frequency and time and, via an array of transmit and receive antennas and some fancy signal processing, yields much higher spectral efficiency than is otherwise possible. Most people exposed to MIMO for the first time are skeptical at best (reminds me of CDMA in 1992), underscoring the adage that any sufficiently advanced technology is indistinguishable from magic. But MIMO works, and it's going to be perhaps the most influential radio technology of the next few years.

I predict the 802.11n WLAN standard will include MIMO as a key component. Granted, 802.11n is at least 18 months away, but there's just no other practical way to push the performance envelope at this point. In fact, Airgo Networks is now shipping MIMO-based WLAN products with 108-Mbit/second single-channel throughput. And this is a relatively simple implementation. Installation in a notebook would allow even more antennas, resulting in even more throughput. And, of course, one can trade off throughput for more range or greater reliability.

I've always expected MIMO to play a major role in radio systems, but my assumption was that we'd see it first in wide-area wireless data systems, not WLANs. And, in fact, we can now look forward to the application of MIMO in WWANs and wireless systems of all forms.

MIMO in cell phones? Sure. MIMO getting us to 200 Mbits/s and beyond in WLANs? I'd bet on it.

One thing is always true in networking: More performance is never enough. MIMO, though, is our best hope to meet the throughput and range demands that are certain to materialize shortly.

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