1. Process for selecting a Precoding Matrix Index (PMI) in a Multiple In Multiple Out (MIMO) receiver of a wireless communications comprising a base station communicating with User Equipments through a downlink and uplink channel, said base station applying a precoding on the transmit symbol vector based on a matrix W i being selected from a set of predefined matrices and identified by a PMI index computed by said UE and forwarded to said base station via said uplink; said process involving step of: estimating the MIMO channel matrix H of a given set of resources blocks comprising received symbol vectors; computing for each particular matrix comprised within said set of predefined matrix a cost function F i (W i , H) being representative of the orthogonality of said matrix MIMO channel matrix H; comparing the values of said cost function Fi; and transmitting to said base station the index i maximizing or minimizing said Fi cost function.