Here, en is a 4-element selection vector with all zeros except for the nth element with 1.
In Equation 14, W2 is configured by vertically concatenating two Y vectors, and the lower Y vectors is multiplied by one of 1, ?1, j, and ?j to compensate for phase rotation between a horizontal beam group and a vertical beam group in an X-pol antenna. In general, 1, ?1, j, and ?j are referred to as a co-phasor factor. Similarly, in Equation 15, (1, ?1) and (j, ?j) are considered as a co-phasor factor.
Hereinafter, an index of W is defined as i1, and i1 is the same as index n of W1 in the aforementioned equation of 4Tx codebook.
An index of W2 is defined as shown in the following table.