Wireless 802.11 N and MIMO

Demand for wireless LAN networks has experienced exponential growth during the past several years, evolving quickly from novelty into necessity. As a measure of this expansion, WLAN equipment shipments in 2008 surpassed the 400-million-unit mark.

The newest wifi network standard is 802.11n (sometimes you can see this referred to as wireless-N). It is considered the Next-Generation standard of wireless network technologies since it improves both data speed and coverage range.

All previous wifi 802.11 standards were working mostly at 2.5 GHz (or 5 GHz for 802.11a) with 20 MHz channel bands. Now, the new 802.11n standard still works at 2.5 GHz, but it uses 40 MHz band channels, resulting in greater data speeds. The data transmission rate supported by 802.11n is 248 Mbps, although the standards talks about even higher data rates.

The MIMO technology used in the standard (MIMO = Multiple In Multiple Out), exploits a radio-wave phenomenon called multipath: transmitted information bounces off walls, doors, and other objects,  reaching the receiving antenna multiple times via different routes and at slightly different times. MIMO harnesses multipath with a technique known as space-division multiplexing. The transmitting WLAN device actually splits a data stream into multiple parts, called spatial streams, and transmits each spatial stream through separate antennas to corresponding antennas on the receiving end. The current 802.11n draft provides for up to four spatial streams, even though compliant hardware is not required to support that many. This technique helps to increase both the data rate and the wireless distance coverage.

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