rted for the entire reporting bandwidth (wideband feedback). In con- trast, the matrix W2 encompasses short-term frequency-dependent characteristic of the chan- nel. Thus the precoder matrix can be selected and reported on a subband basis where a subband covers a fraction of the overall reporting bandwidth. Alternatively, the device may decide not to report W2 when subsequently selecting CQI. In that case, it should assume that the network randomly selects W2 on a per physical resource block group basis. New Radio Access Physical Layer Aspects (Part 2) 505 Note that this does not impose any restrictions on the actual precoding applied at the gNB side, rather it is only about the assumptions that the device would make when selecting CQI. The matrix W1 can be considered as defining a beam or a group of beams pointing toward a specific direction. More specifically, the matrix W1 can be written as where each column of the matrix b defines beam. The 2 of a structure the matrix corresponds to two polarizations. Note that, as the matrix W1 is assumed to rep- resent long-term frequency-independent channel characteristics, the same beam direction can be assumed to fit both polarization directions. Selecting matrix W1 or equivalently b can be seen as selecting a specific beam direction from a large set of possible beam direc- tions defined by the full set of W1 matrices within the codebook. In the case of rank 1 or rank 2 transmissions, either a single beam or four adjacent beams are defined by the matrix W1 (see Fig. 4.42). In the case of four adjacent beams corresponding to four columns in matrix b, matrix W2 would select the exact beam to be used for the transmission. Since W2 can be reported on a subband basis, it is possible to adjust the beam direction per subband. In addition, W2 provides co-phasing between the two polarizations. In the case where W1 only defines a single beam corresponding to b being a vector, matrix W2 would only pro- vide co-phasing between the two polarizations. For transmission ranks R>2 the ma