Patent ID: 8750404

Claim:
A method, comprising: in a mobile communication terminal, holding a definition of a sub-sampled codebook identifying precoding matrices to be used for providing precoding feedback by the terminal, wherein the precoding matrices in the sub-sampled codebook are selected from a master codebook that is made-up of a first sub codebook and a second sub-codebook, wherein the first sub-codebook represents a first precoding component and the second sub-codebook represents a second precoding component that varies more rapidly than the first precoding component, and wherein the definition defines a first subset of the first sub-codebook and a second subset of the second sub-codebook; receiving in the terminal a Multiple-Input Multiple-Output (MIMO) signal via multiple receive antennas; and based on the received MIMO signal, selecting from the sub-sampled codebook a precoding matrix for precoding subsequent MIMO signals transmitted to the terminal, and calculating the precoding feedback indicating the selected precoding matrix by choosing one of the precoding matrices from the first subset and combining an indication of the chosen precoding matrix with a Rank Indication (RI) to produce four or five bits of the precoding feedback, wherein the combined indication of the chosen precoding matrix and the RI comprises five bits, wherein the first sub-codebook is formed of sixteen precoding matrices having indices {0 . . . 15}, and wherein choosing the precoding matrix comprises choosing the matrix from among the precoding matrices having the indices {0,2,4,6,8,10,12,14}.