eam widths will be smaller. Therefore, even for large numbers of UEs, there will be much fewer UEs within a certain beam, so larger CB sizes will be required. Up to now in the LTE, single-sector MU-MIMO or SDMA has been inves- tigated. In that case, there is a good chance that one beam selection fits for the full frequency band or all RBs. If we take a look at Figure 7.12 (bottom), there are two beams. As it is depicted, it fits in an open-loop scenario because beam separation is kept at all locations. In reality, multi- path effects will intermix both beams, generating some mutual beam inter- ference. From a cooperation perspective, it is more important that in the case of, for example, inter-eNB cooperation, AEs will be placed at different locations, generating generalized beam patterns. These are by no means orthogonal and show fast fluctuation from RB to RB, SO feedback per RB will be required. For our approach, the precoding matrix W is selected from a ZF or MMSE codebook, which means that W is the Morse Penrose pseudoinverse of the quan- tized channel matrix = WA,PHI =H+; PMI-A = quant(abs(b);)); PMI- quant(angle (bi,i)); i = 1,...,2; j = 1, 2. The quantize operation is "quant," which uses A bits for the amplitude value PMI-A, and phi bits for the angle PMI-o, i,j' SO the accuracy under the assumption of normalized radio channels his is for PMI-A, equal to 1/2^A and of the angle PMI- i,j equal to 1/2^PHI. Normalization includes the adaptation to different path loss values on each UE link, which can be estimated and corrected from wideband received signal strength indication (RSSI) measurements. The pertinent codebook, CA,PHI, consists of (2^A 2 2 PHI)^2 complex valued 2x2 matrices. The squaring is due to the fact that UE1 and UE2 feed back one value each, which leads to a combined codebook that is of higher dimension. Amplitude as well as phase values are fed back separately. Our own investi- gations as well as those of other research groups have shown the importance of amplitude in addition to that of phas