een used. The data rate of 300 Mb/s per site or 100 Mb/s per sector is a rough estimate for a baseline LTE implementation with 2 AEs per sector. In DL, peak data rates of almost 170 Mb/s per sector would be possible, but the averaging of cell center and cell edge users will reduce the mean data rate per cell significantly; 100 Mb/s is just a rough estimate allowing for easy calculation. In Figure 7.11a, a conventional network as benchmark for data traffic on S1, X2 and WL links is given. In this simple case, each site with three eNBs has to transmit 300 Mb/s over the S1 interface and no traffic over X2 or WL. Figure 7.11b assumes availability of fiber connections, over which RRHs are attached to the CU. In this case, it might even be possible to support the very high data rates of more than 10 Gb/s per site, which result from the OBSAI interface for several AEs. Figure 7.11c is a solution where the CU receives all data for all eNBs over the S1 interface. Over the X2 interface, the CU receives CSI information from all eNBs, calculates proper precoding matrices, performs the precoding, and quantizes the resulting Tx (transmit) signals before these are transmit- ted to the neighboring sites. With optimum quantization and selection of cooperating UEs, the data rate over the X2 interface might be reduced significantly compared to solution 7.11b. In the case of 7.11b, RF signals have to be transmitted to the RRHs, but here just the quantized baseband signals are used. In Figure 7.11d, the benefits of mirror CUs are being evaluated. This concept reduces data traffic for the X2 significantly. All data for all UEs are multi- casted to all sites SO that overall data traffic on S1 interfaces is tripled. In Figure 7.11e, the concept of mirror CUs is extended to the previously described DSO system, where control and channel information is also exchanged over the air SO that there is no data traffic on X2. At the same time, UEs must exchange and broadcast control and CSI information in the form of PMI values over the air on th