coefficients in W2 is also included in W1. Therefore, the amplitude component of the linear combination coefficients comprises wideband and subband components. The phase compo- nent is per subband and configurable as QPSK or 8-PSK. Due to large degrees of freedom offered by Type II CSI, the number of precoder hypotheses is large. However, exhaustive codebook search, which is prohibitively complex, is not needed. Due to high spatial resolu- tion, the precoder can be efficiently determined by performing scalar quantization of each of the channel eigenvector coefficients. Since Type II CSI is configurable in terms of its basis set size Le {2, 3, 4}, the amplitude frequency granularity, that is, wideband-only or wideband + subband, and phase shift (QPSK or 8-PSK), a range of performance-overhead trade-offs would be possible [57]. There are two subtypes of Type I CSI that are referred to as Type I single-panel CSI and Type I multi-panel CSI, corresponding to different codebooks. These codebooks are designed assuming different antenna configurations on the gNB transmitter. The codebooks for Type I single-panel CSI are designed assuming a single antenna panel with NH X Nv cross-polarized antenna elements. In general, the precoder matrix W for Type I single-panel CSI can be constructed as the product of two matrices W1 and W2 where the information 504 Chapter 4 selection Co-phase selection b0,b1,b2,b3 Type-I CSI: The UE selects beam and co-phase; i.e., the relative phase difference between cross-polarized antennas, coefficients P2 = e.jup Bupbi Type-II CSI: The UE selects multiple beams, amplitude scaling, and phase coefficients for linear combination among the beams Beam group selection Amplitude scaling Co-phasing and linear combination Wideband Per subband Figure 4.42 Illustration of Type-l and Type-II CSI in NR (57,69]. about the selected W1 and W2 is reported separately in different parts of the PMI. The matrix W1 captures long-term frequency-independen characteristic of the channel. A single W1 is selected and repo