ined, X2 provides latencies of less than 20 ms and allows for fast tunneling of user data over GTPs (GPRS tunneling protocols; for more information, see 3GPP 36 series of specifications). The main targets are gigabit Ethernet lines, SO data rates in the order of 1 Gb/s should be possible. For comparison of the different COOPA concepts, some simplifying basic assumptions have been made: Each cooperation area consists of three eNBs. The two strongest out of three eNBs cooperate (2 X 2, 2 X 2) MIMO. RF bandwidth is 20 MHz or 100 RBs. Mean data rate per eNB is dNB = 100 Mb/s. Three sectors with two antenna elements each per site data rate per site: dsite = 300 Mb/s. S1 = gigabit Ethernet preferred solution. X2 interface = <20 ms latency; GTP tunnel over gigabit Ethernet. Typical scheduling overhead is based on rough estimation (10-30% for one to three control symbols per subframe). For a more accurate estima- tion, see Chapter 8. The following data rates will be used for comparison of the different proposals: Data rate dOBSAI is the data rate on the OBSAI interface between the baseband processing unit and RF-FE. The sampling rate is 20 MSps with four times oversampling and a quantization QOBSAI of 16-20 bit per data stream or per antenna dOBSAI = 1.3 Gb/s per antenna element. CSI data rate dCSI is the data rate for the feedback of CSI estimates from UEs to the CU. Similar signal and IF power for all scheduled UEs is assumed, allowing for a reduced CSI quantization. Note that, together with path loss © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3GPP LTE Radio and Cellular Technology information, this restriction can always be fulfilled. Full-band CSI for all RSs is assumed: 200 RSs in four symbols per antenna and subframe (APs 1 and 2) and 200 RSs in two symbols for APs 3 and 4 subframe length of 1 ms quantization QCSI = 2-6...10 bit (depends on MCS and intended SINR) dCSI = 200 4 * Qcs1/1 =1.6...8 Mb/s per antenna CB-based precoding data rate dCB is the data rate for feeding back PMI val- ues for precod