Reference signals for validation in a MIMO downlink channel wireless multicarrier

A method comprising: determining (92) a matrix link beam for a transmission device (12) to use for precoding data for transmission to a receiving device (14) via a MIMO channel multicarrier where determination is made at said receiving device, said matrix link beam a plurality of columns comprising; transmitting (94) data from said receiving device to said transmitting device, identifying said parent link beam; receiving (96) signals dedicated pilots (82) and data signals from said transmission device, through said channel MIMO multicarrier, which were supposed to have been precoded by said transmission device using said matrix link beam, with said pilot signals dedicated including known information; and processing said pilot signals dedicated to validate (98) if said transmission device has actually used such parent link beam for precoding said signals dedicated pilots and said data signals; wherein processing said pilot signals dedicated to validate whether said transmission device actually used said matrix link beam for precoding said signals dedicated pilots and said data signals includes using a maximum likelihood detection for processing said pilot signals dedicated; using the maximum likelihood detection for processing said pilot signals dedicated involves searching codebook reduced complexity which includes a search column as follows: said method characterized by ** Formula ** where vi * is the estimate of the i-th column of the matrix link beam actually used by the transmitting device, Yi is the ith column of the pilot signal dedicated received Y, H is the channel matrix and Codebook is the book code possible matrices link beam and Ns is the number of spatial streams.