A method comprising: (a) receiving a radio signal transmitted from a transmitting device over a wide channel by a receiving device in an OFDMA wireless system, wherein the radio signal is transmitted over multiple sub-channels of the wide channel; (b) estimating channel quality information based on the received radio signal for each sub-channel; and (c) sending feedback information to the transmitting device, wherein the feedback information contains individual estimated channel quality information for each sub-channel of selected sub-channels from the wide channel, wherein the selected sub-channels comprise all sub-channels or the best sub-channel or sub-channels with a signal to noise ratio, in the following referred to as SNR, over a predefined threshold or N best or N worst sub-channels, where N is a predefined number, and the channel quality information comprises an average SNR over all spatial streams of said each sub-channel or the feedback information contains the sum throughput of all spatial streams on each sub-channel; and the feedback information for said each sub-channel is piggybacked into a corresponding acknowledgement, in the following also referred to as ACK, frame or a corresponding block acknowledgement, in the following also referred to as BA, frame sent by the receiving device, characterized in that the ACK frame or the BA frame comprises a sub-channel feedback element, and the feedback information is embedded into the sub-channel feedback element of the ACK frame or the BA frame, and the method further comprises: receiving a channel state information, in the following also referred to as CSI, feedback request for an MU-MIMO sub-channel from the transmitting device by the receiving device, wherein the MU-MIMO sub-channel is selected by the transmitting device based on the received feedback information; and sending a compressed channel matrix report of the MU-MIMO sub-channel from the receiving device to the transmitting device. (a) receiving a radio signal transmitted from a transmitting device over a wide channel by a receiving device in an OFDMA wireless system, wherein the radio signal is transmitted over multiple sub-channels of the wide channel; (b) estimating channel quality information based on the received radio signal for each sub-channel; and (c) sending feedback information to the transmitting device, the feedback information contains individual estimated channel quality information for each sub-channel of selected sub-channels from the wide channel, wherein the selected sub-channels comprise all sub-channels or the best sub-channel or sub-channels with a signal to noise ratio, in the following referred to as SNR, over a predefined threshold or N best or N worst sub-channels, where N is a predefined number, and the channel quality information comprises an average SNR over all spatial streams of said each sub-channel or the feedback information contains the sum throughput of all spatial streams on each sub-channel; and the feedback information for said each sub-channel is piggybacked into a corresponding acknowledgement, in the following also referred to as ACK, frame or a corresponding block acknowledgement, in the following also referred to as BA, frame sent by the receiving device, characterized in that the ACK frame or the BA frame comprises a sub-channel feedback element, and the feedback information is embedded into the sub-channel feedback element of the ACK frame or the BA frame, and the method further comprises: receiving a channel state information, in the following also referred to as CSI, feedback request for an MU-MIMO sub-channel from the transmitting device by the receiving device, wherein the MU-MIMO sub-channel is selected by the transmitting device based on the received feedback information; and sending a compressed channel matrix report of the MU-MIMO sub-channel from the receiving device to the transmitting device. receiving a channel state information, in the following also referred to as CSI, feedback request for an MU-MIMO sub-channel from the transmitting device by the receiving device, wherein the MU-MIMO sub-channel is selected by the transmitting device based on the received feedback information; and sending a compressed channel matrix report of the MU-MIMO sub-channel from the receiving device to the transmitting device.