essing delay in the UE (L2 and RRC) Transmission of RRC Connection Set-up complete Processing delay in eNB (Uu -> S1-C) S1-C Transfer delay MME Processing Delay (including UE context retrieval of 10ms) S1-C Transfer delay Processing delay in eNB (S1-C-Uu) Transmission of RRC Security Mode Command and Connection Reconfiguration + III alignment Processing delay in UE (L2 and RRC) C-Plane Delay The calculation of the user-plane latency was carried out for synchronized (or pre-scheduled) UEs. In the case where the UE is not pre-scheduled or when the UE is required to synchronize in order to be allocated uplink resources, a reduced RACH scheduling period, a shorter PUCCH cycle, and reduced processing delays can be applied to satisfy the user-plane latency requirements. The 3GPP LTE-Advanced general handover procedure is based on that of 3GPP LTE, which was described in Chapter 6, and is illustrated in Figure 12-23. The model shown in the figure has been used for calculation of the handover interruption time. As shown in Figure 12-14, once the handover command has been processed by the UE, the UE detaches from the source eNB and stops receiving data. This marks a point in time where the user-plane connectivity is interrupted. The UE then performs frequency synchronization with the target eNB, depending on whether the target cell is 12.10 3GPP LTE-advanced link-level and system-level performance Serving Target eNB HO Preparation HO Command Data Forwarding Processing 1) Radio Synch 2) RACH Waiting 3) RACH Preamble 4) Processing 5) Grant 6) Processing 7) Data Transmission FIGURE 12-23 Model for calculation of handover interruption time [40] operating on the same carrier frequency as the currently served frequency. Since the UE has already identified and measured the target cell, the corresponding delay will be negligible. The UE then performs downlink synchronization. Although baseband and RF timing alignments are part of the delay budget, since the UE has already acquired downlink synchronization with the target cell in 