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802.11n - technical definition

The developing IEEE standard (estimated March 2009) for an 802.11 wireless local area network (WLAN) operating in the 2.4-GHz band and operating at a signaling speed of up to 108 Mbps, with an option to increase speed to as much as 600 Mbps. 802.11n will be backward-compatible with 802.11a/b/g, building on them by introducing antenna technology known as multiple-input multipleoutput (MIMO), which is based on the concept of spatial diversity.The transmitter splits the signal among multiple transmit antennas separated by some amount of space, but operating on the same frequency at the same time. The multiple receive antennas gather the signal, which has suffered from the effects of multipath propagation. Some signal elements will be stronger than others and will arrive ahead of others. Sophisticated signal processing software combines and correlates many signal elements arriving at different times into one linear combination of a stronger, synchronized, intelligible signal derived from each of the receive antennas and reconstitutes the original data stream. See also 802.11a, 802.11b, 802.11g, IEEE, frequency, MIMO, multipath propagation, and spatial diversity.

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An IEEE 802.11 wireless network standard that increases transmission speeds to 100 Mbps and beyond. The final standard is expected in 2009. Because 802.11n works in both the 2.4 GHz and 5 GHz frequency bands, it is compatible with legacy 11a and 11b/g users (see dual-band router).

Multiple Antennas (MIMO)
The key to the 802.11n standard is the use of multiple antennas. "Multiple input/multiple output" enables two data streams to be sent simultaneously over longer distances. See MIMO.

Pre-N and Draft-N
In 2004, Belkin was the first vendor to introduce a "Preliminary-802.11n" access point and laptop card using its own ingenuity and the latest drafts from the IEEE. Both access point and laptop cards had to be from Belkin. Other vendors followed with their own proprietary "Pre-N" equipment.

In 2007, the Wi-Fi Alliance launched its certification system to validate 802.11n equipment using Draft 2.0 of the specification so that different vendors' equipment could work together. Referred to as the "Draft-N" standard, firmware upgrades may be required to bring Draft-N devices up-to-date when the final standard is ratified. See MIMO and 802.11.

Pre-N Equipment

Introduced in 2004, this Belkin wireless router uses two transmitters and three receivers to deliver a maximum speed of 108 Mbps. (Image courtesy of Belkin Corporation, www.belkin.com)

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