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802.11n Theory of Operation

Formation of 802.11n group

Even though the maximum PHY layer rate is around 50 Mbps, the net throughput obtained is only 60 percent in indoor applications. To increase the net throughput on par with Ethernet, the task group 'n' was formed in January 2004 and many proposals were reviewed to achieve this goal.

The three main proposals are WWiSE, TGnsync and EWC (WWISE 2005, TGnsync 2005 and EWC 2006). All three proposals utilize multiple transmit and multiple receive antennas called as multiple-input multiple-output (MIMO) technology. This technology allows one to transmit multiple independent data streams simultaneously to increase the spectral efficiency. This is also known as spatial multiplexing. To counter the multipath nature of the channel, OFDM coding is used along with MIMO technology.

Therefore, the final system is categorized as a MIMO-OFDM system. The three proposals mandate 20 MHz operation and support for 40 MHz operation. They also mandate the interoperability with the legacy 802.11a/g systems.

The maximum PHY data rate that can be achieved with four transmit antennas in 40 MHz is approximately 500 Mbps. On the MAC side, all the proposals support frame aggregation, block acknowledge (BACK) and MAC header compression.

In January 2006, the EWC proposal was finalized as the draft for the 802.11n standard. Apart from the above features, this supports advanced techniques for optional modes. They are adaptive beamforming, space time block coding (STBC) and low density parity coding (LDPC) for increased range and reliable communications.

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