Sunday, July 15, 2012

Wi-Fi latest Standards -802.11n

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Wi-Fi Alliance logoWi-Fi Alliance logo (Photo credit: Wikipedia)802.11n:
IEEE released the first Wi-Fi standard in 1997 and has since adopted 802.11a, b, g, and n versions. 802.11n, approved in 2009, operates in the 2.4- and 5-GHz frequency bands and offers a theoretical maximum throughput of 150 Mbits per second per data stream.

Although IEEE 802.11n was released more than two years ago, Wi-Fi equipment has not advanced enough to use all of the approach’s capabilities.

Multiple data streams
802.11n is designed to work with multiple-input, multiple-output technology. MIMO increases throughput by using multiple antennas on both transmitters and receivers, enabling more than one data stream.
IEEE 802.11n allows up to four data streams at a time by enabling the use of four antennas on the transmitter and four on the receiver, a configuration known as 4 × 4. This would yield a theoretical maximum data rate of 600 Mbps per chip (150 Mbps per data stream), and increase the maximum transmission range.

Vendors such as Qualcomm have announced chips that enable 4 × 4 but haven’t shipped any products yet, noted Craig Mathias, founder of the Farpoint Group, a wireless communications advisory firm.

Numerous vendors, such as Hewlett-Packard, have released 3 × 3 systems already, though, for use in products such as APs. These chips let the APs either offer 50 percent more bandwidth or handle 50 percent
more clients at the same bandwidth than products offering just two data streams.

Beam forming
802.11n enables Wi-Fi to use beam forming to improve performance. With this technique, the Wi-Fi infrastructure sends out multiple signals and analyzes client feedback to determine the optimal path that signals should take to reach the client. It then shapes the signal beam appropriately.
Vendors are selling equipment for large corporations that use beam forming, said Mathias, but the approaches are typically proprietary.
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