What is Cyclic-Delay Diversity (CDD)?
In addition to actively forming beams towards the receiver, the 802.11n draft standard also includes a scheme for preventing unintentional beamforming. This can occur if the data being transmitted down the various spatial streams inadvertently forms correlated patterns, i.e., similar data sequences that are synchronized to each other; for example, a binary sequence such as ‘10101010…’ will split among the antennas such that the signals emitted from all the antennas are phase-aligned. In a situation where the transmitted signals from multiple antennas are coherent in amplitude and phase, the radiation pattern will form beams. This is much like the manner in which antenna arrays obtain their directive characteristics by feeding multiple antennas with phase-shifted copies of the same signal. Unlike intentional beamforming, however, the pattern of lobes and nulls may not be oriented in such a way as to maximize the effect at the receiver, and thus unintentional beamforming can be detrime
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- What is Cyclic-Delay Diversity (CDD)?
