METHOD, APPARATUS AND COMPUTER PROGRAM FOR CONTROLLING A WIRELESS DEVICE

A double structured codebook is described that has a wideband codebook portion C(W1) and a frequency-selective codebook portion C(W2). Portion C(W2) is characterised in that for at least one rank index RI, each codeword of C(W2) is uniquely distinguished over all other codewords of C(W2) by at least two beam selection vectors per layer. A device (UE, eNB, etc) utilises the at least two different beam selection 10 vectors per layer to uniquely select a codeword W2 from C(W2) (404); and constructs a pre-coder W from the selected codeword W2 and from another codeword W1 selected from the wideband codebook portion C(W1) for signalling channel conditions (406). An additional co-phasing term for ensuring orthogonality can be utilised with the beam selection vectors per layer to uniquely select the codeword from C(W2), and the two different beam selection vectors per layer correspond to different polarizations (410).