This phase differential introduces noise and distortion that you can hear as the car moves within the city, in the form of signal fading, intermittent reception (also called picket-fencing) and sudden signal dropouts. In digital communications, these factors can cause a reduction in data speed and an increase in the number of errors.

Adding antennas, as some wireless systems do, helps sort out signals, allowing the receiver to pick the antenna getting the strongest signal at any given point. How many antennas? Netgear Inc. in Santa Clara, Calif., has recently offered products using seven internal antennas, which combine to create up to 127 different antenna patterns. This is called diversity reception, and though it's not a true MIMO, it's just the beginning of what can be done with multiple antennas.

MIMO can use the additional signal paths to transmit more information and recombine the signals on the receiving end. It's analogous to our ability to readily localize, using just our two ears, the origin of specific sounds or to isolate and understand one conversation fragment from the midst of assorted cocktail party chatter. Using multiple receivers in this way isn't a newly discovered phenomenon; it's been used in some radio transmission for at least half a century. But until recently, the amount of signal processing needed has been too expensive to be practical. An important factor driving MIMO acceptance today is the advent of inexpensive, high-speed chips with millions of transistors.

MIMO systems can use spatial multiplexing to distinguish among different signals on the same frequency. Moreover, we can encode these transmissions so that information on each can be used to help reconstruct the information on the others. Called space-time block coding, you can think of this as akin to parity or other error-detection and -correction schemes -- they allow us to increase reliability in addition to pure throughput.

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