e mainly placed near the tallest buildings, in order to offload Small Cell Optimization Europe Tokyo 3 kmph 30 kmph 60 kmph Figure 8.13 Handover failure (HOF) percentage for different scenarios without DC and carry more traffic where the radio signal from macro cells is typically weaker and there is higher traffic. For the site-specific scenarios, the users move along the streets, while users are free-moving for the 3GPP scenario as defined in Reference 7. We focus on the RRC connected mode downlink performance. The mobility management is based on UE measurements and controlled by eNodeBs. The UE measurement quantities are reference signal received power (RSRP) or reference signal received quality (RSRQ). The RSRP is essentially a measure of the received power of the transmitted reference signal from a cell, while the RSRQ equals the RSRP/RSSI ratio, where RSSI is the received signal strength indicator, or equivalently the total wideband received power. The UE can be configured to perform measurements of RSRP and RSRQ from its serving and surrounding cells. The RSRP and RSRQ are measured at the physical layer, followed by additional time-domain filtering at Layer-3 using a first-order auto regressive filter. For additional details and background on the assumed RRM measurement events for PCell and SCell mobility/cell-management events, see References 8 and 9. Figure 8.13 shows the HOF rate for the case without DC, while Figure 8.14 shows the corresponding performance results when DC is enabled. In this context, a HOF event is declared if RLF occurs after TTT expires, during the handover execution time as defined in [8]. Note that RLF is only declared based on radio link monitoring of PCell connection quality by the UE. As observed from Figure 8.13 (results without DC), the probability of experiencing HOFs is relatively low at the different speeds. The lowest HOF probability is observed for the generic 3GPP simulation scenario, while higher HOFs are found for the site-specific cases. A closer inspection of the HOF 