A MIMO primer

Multiple-input multiple-output (MIMO) wireless uses different waveforms on typically two, but sometimes three or more transmitting antennas inputting to the channel carrying radio waves from Point A to Point B. Multiple antennas and radios (typically, two or three) also are applied to the output of the radio channel at the receiver, along with a lot of signal processing, which ideally improves range and throughput compared with simpler or traditional radio designs operating under similar conditions.

MIMO is sometimes referred to as spatial multiplexing, because it users a third, spatial dimension - beyond frequency and time - as a carrier for information. The multiplicative effect of properly designed MIMO systems can be dramatic: As our tests show, the 100Mbps barrier (application-layer throughput) in wireless LANs has been broken. Indeed, the upcoming 802.11n standard will likely specify raw (physical layer) performance as high as 600Mbps via a 4-by-4 MIMO array.

MIMO is also likely to have an influence on so-called 4G cellular designs, but that's a different story.

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Copyright © 2006 IDG Communications, Inc.

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