This occurs in 802.11n when a transmitter and receiver work together to educate each other about the characteristics of the MIMO channel. The transmitter will make phase adjustments based on the information that is returned from the receiver. When using explicit feedback, the beamformee makes a direct estimate of the channel from training symbols sent to the beamformee by the beamformer. The beamformee takes that information and sends additional feedback to the beamformer. The beamformer then transmits based on the feedback from the beamformee.