 Number of No Small Ports Used Layers V Delay {0,1} {0,1,2,3} e-j2n-38 where the precoding matrix W(i) is of size P X V and i = 0,1, Maymb-1 layer symb* The diagonal size UX V matrix D(i) supporting cyclic delay diversity and the size UX V matrix Uare both given in Table 5.1 for different numbers of layers V. The values of the precoding matrix W(i) should be selected from among the pre- coder elements in the codebook configured in the eNodeB and the UE. The eNodeB can further confine the precoder selection in the UE to a subset of the elements in the codebook using codebook subset restriction. The configured codebook should be selected from Table 5.5 or Table 5.6. Table 5.4 Large-Delay Cyclic Delay Diversity Number of Layers V e-j2n/2 e-j2ril2 1 e-j2n/3 e-j4r/3 e-j81/13 e-j4n/4 e-j6r/4 e-j2ri/4 e-j12/4 e-j6n/4 e-j18t/4 e-j6ri/4 C 2009 by Taylor & Francis Group, LLC MIMO OFDM Schemes for 3GPP LTE Table 5.5 Codebook for Transmission on Antenna Ports {0,1} Number of Layers V Codebook Index 11/11/19 5.2.3.5 Codebook for Precoding The precoding is used to convert the antenna-domain MIMO signal processing into the beam-domain processing. For two transmit antennas, it was decided that the unitary precoding matrix is to be used for support of SU-MIMO. Also, UE feedback is based on the codebook-based precoding for frequency-domain duplexing (FDD). For transmission on four antenna ports, the quantity Wist denotes the matrix de- fined by the columns given by the set {s} from the expression Wn=I = - where I is the 4x4 identity matrix and the vector un is given by Table 5.6. The codebooks for various ranks for four antennas are constructed as follows [5]: Choose rank-one codebook. The rank-one codebook consisting of some N unit-norm 4 X 1 complex vectors is chosen. Note that the codebook can be chosen to satisfy any metric. We evaluate two codebooks here: one is a Grassmanian-based codebook optimized to achieve high throughput for correlation antennas; the other is a constant-modulus Grassmanian code- book optimized to achiev