trix W1 defines Nbeams orthogonal beams where Nbeams = [R/2]. The Nbeams beams, together with the two polarization directions in each beam, are then used for transmission of the R layers, with the matrix W2 only providing co-phasing between the two polarizations. The NR sup- ports transmission of up to eight layers to the same device [14]. In contrast to single-panel CSI, codebooks for Type I multi-panel CSI are designed assum- ing the joint use of multiple antenna panels at the network side considering that it may be difficult to ensure coherence between transmissions from different panels. More specifically, the design of the multi-panel codebooks assumes an antenna configuration with two or four two-dimensional panels, each with NH X Nv cross-polarized antenna elements. The opera- tion principles of Type I multi-panel and single-panel CSI are similar, except that the matrix W1 defines one beam per polarization and panel, whereas matrix W2 provides per-subband co-phasing between polarizations as well as panels. The Type I multi-panel CSI supports spatial multiplexing with up to four layers. Type II CSI provides channel information with significantly higher spatial granularity com- pared to Type I CSI. Similar to Type I CSI, Type II CSI is based on wideband selection and reporting of beams from a large set of beams. However, while Type I CSI selects and reports a single beam, Type II CSI may select and report up to four orthogonal beams. For each selected beam and each of the two polarizations, the reported PMI then provides an amplitude value (partly wideband and partly subband) and a phase value (subband). This allows constructing a more detailed model of the channel, capturing the main rays and their 506 Chapter 4 respective amplitudes and phases. At the network side, the PMI received from multiple devices can be used to identify a set of devices with which transmission can be done simul- taneously on a set of time/frequency resources, that is, MU-MIMO, and what precoder to use for each transmission. Since Ty