n 12.5, the handover success rate has a strong impact on the dropped call rate. Good neighbour plan is the basis for high handover success rate. Good neighbour plan means that each cell has all the main handover target cells defined as neighbours. The most optimal neighbour plan can be achieved with the 3GPP-defined ANR feature. The ANR feature operation is introduced in [8]. The ANR feature can automatically add neighbours based on the UE measurements provided that this neighbour is good enough target cell. There can be several unnecessary neighbours added as well and therefore the ANR feature requires additional neighbour relation removal which can then remove seldom used neighbours or neighbours that have very low handover success rate. Enabling the ANR feature shows significant improvement in dropped E-RAB rate caused by the handover execution problems (basically handover signalling problem) and improvement in handover success rate as shown in Figure 12.34. LTE Key Performance Indicator Optimization Change in RRC setup attempts Change in E-RAB drop rate 0.00% -0.01% -0.02% -0.03% -0.04% -0.05% -0.06% After, day 1 After, day 2 After, day 3 After, day 4 Figure 12.33 PUCCH closed-loop power control decision window tuning gain. Network-level statistics 2 days before the parameter tuning are compared to the statistics samples taken on four consecutive days after the parameter tuning E-RAB drop rate Handover execution success rate enabled Figure 12.34 E-RAB drop rate caused by handover signalling problems and handover execution success rate before and after enabling ANR feature. Network-level hourly statistics collected for 11 days LTE Small Cell Optimization enabled Figure 12.35 Handover decision success rate before and after enabling the ANR feature. Network-level hourly statistics collected for 11 days Another gain from ANR is the improvement in handover decision success rate, that is, the ratio between started handover procedures to sum of started and not started handover procedures. In case source eNodeB recei