quences to occupy a total of 564 (Rel-10 MU-MIMO/CoMP with 6 MBSFN subframes per 10 ms) and 528 (Rel-8 downlink SU-MIMO) resource elements per radio frame for downlink eight- and four-layer spatial multiplexing, respectively. In addition, the UL/DL configuration 1 (2 DL subframes, 1 special- subframe, 2 uplink subframes) and special-subframe configuration 4 (12 DwPTS, 1 GP, 1 UpPTS, UpPTS is used for SRS transmission) are assumed for the TDD mode. The results shown in Table 12-22 suggest that the 3GPP LTE Rel-8 already fulfills the ITU-R requirements for downlink peak 12.10 3GPP LTE-advanced link-level and system-level performance 50% Point of Uplink SINR CDF Uplink SINR (dB) FIGURE 12-20 Statistical distribution of the uplink SINR in various test environments [42] spectral efficiency. The table also shows the additional performance that can be achieved using advanced technical features, e.g., downlink eight-layer spatial multiplexing. The uplink peak spectral efficiency is calculated assuming a 20 MHz bandwidth, PUCCH occu- pying two pairs of resource blocks per subframe, and PRACH consuming six resource block pairs per radio frame. The same UL/DL and special-subframe configurations are assumed for the downlink peak-spectral efficiency calculation. Table 12-22 shows that the extension of the 3GPP LTE Rel-8 with two-layer spatial multiplexing can fulfill the ITU-R requirement in the uplink. 12.10.5 User-Plane/Control-Plane Latency and Handover Interruption Time The LTE user-plane one-way access latency for a scheduled UE consists of fixed node processing delays, which include radio frame alignment and 1 ms TTI duration. Using the latency calculation model shown in Figure 12-21, and assuming that the number of HARQ processes is eight for the FDD mode, the one-way latency is given as TUSER-PLANE = 4 + 8p where p is the probability of HARQ re- transmissions or the error probability of the first HARQ re-transmission. While the minimum latency of TUSER-PLANE = 4 ms is achieved for p = 0, a more realistic value of TUSE