may be transmitted after it is transformed by inverse fast fourier transform ifft circuit 135 the receiving unit 150 may be configured to separate the received signal after processing by fast fourier transform fft circuit 180 data separator circuit 185 is provided to separate the received signal into three branches common pilot dedicated pilot and data the common pilot signals are sent to channel estimation circuit 170 where the wireless channel response is estimated the estimated channel is sent to pmi selector circuit 165 pmi validation circuit 175 and data detection circuit 190 which receives the data branch of the received signal from data separator circuit 185 in pmi selector circuit 165 an optimum precoding matrix is selected from codebook table 155 according to channel conditions the selected precoding matrix is represented by a pmi which is transmitted via transmitter 160 of receiving unit 150 back to transmitting unit 100 for the next data transmission the estimated channel is also sent to pmi validation circuit 175 where the dedicated pilot signal is used to identify the precoding matrix that was actually used to precode the data while the ideal precoding matrix should be identical to the matrix that was sent back to transmitting unit 100 in reality these.