ing from UEs to the CU. A baseline 2 X 2 (two UEs and two eNBs) system leading to an overall 4 X 4 distributed MU-MIMO system is assumed: each UE feeds back PMIs full band, highest granularity 100 RBs per UE and subframe quantization/CB size QCB =<5 bit/10 bit (rank + PMI/increased SINR) dcb = 100 QCB/1 ms=0.5...1 Mb/s per UE Control data rate dControl is the data rate for exchange of scheduling informa- tion between different mirror CUs if distributed schedulers have to be synchronized: 10-30% control overhead (see Chapter 8) dControl = 8...30 Mb/s per cell (24...) Mb/s persite) rate dco is the data rate for feeding back CQI information from UEs to the CU and informing the NBs about possible MCSs for different data streams. The assumption is a baseline 2 X system SO that, at maximum, two data streams can be supported. Adaptation and highest CQI feedback per subframe and for each RB: 100 RBs per data stream and subframe quantization Qcii 5 bit (see LTE R8: 5-bit entry to CQI table) dcQ = 100 * Qcq/1ms = 0.5 Mb/s per data stream QAM data rate dQAM is the data rate in case of a subcarrier (SC)-wise quantiza- tion of the baseband Tx-signals. These signals have to be sent from the CU to each cooperating radio station: full band 1,200 SCs for 14 symbols per antenna port and subframe (APs 1 and 2) quantization QQAM = 2-6...10 bit (QQAM depends on MCS and intended SINR) dQAM = 1200 Mb/s per antenna In Figure 7.11a-f, six different network and COOPA concepts are depicted. For each solution, the data traffic on S1, X2 and the traffic that can be sent wirelessly (WL) have been calculated based on the preceding data rates for dOBSAI dcsp dCB dControl dco and dQAM For each solution, data and control traffic (e.g., for CSI information) are given. For some scenarios, upper bounds and achievable data rates, which can be expected after proper optimization, © 2009 by Taylor & Francis Group, LLC Cooperative Transmission Schemes are given as X2min- or WLopt-values. In this case, lower and upper values for quantization levels have b