802.11n has many new features including Space Time Block Coding (STBC), Spatial Multiplexing (SM), Cyclic-Delay Diversity (CDD), Maximal Ratio Combining (MRC), and Transmit Beam Forming (TxBF). A great summary of these features is found in an Atheros whitepaper here: http://www.atheros.com/pt/whitepapers/MIMO_Pwr3_whitepaper.pdf

Not all of these features are found in all 802.11n equipment, and not all of these features are tested in the Wi-Fi Alliance's (WFA) new 802.11n-draft2.0 certification. For example, STBC Tx 2x1 is manditorily tested by the WFA for the AP only, and Rx is optionally tested. TxBF will optionally be tested, but at a later date. MRC and CDD are not mentioned at all. With so many new enhancements in 802.11n, some of which are not implemented in some products, some of which are not compatibility tested, and most of which are confusing to most users and buyers, my guess is that there's going to be lots of fear, uncertainty, and doubt (FUD) in the market for a while. My suggestion is to do your homework. Don't take anyone's word for interoperability, performance, or features. Build your own pilot for every implementation.

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