ves measurement report that indicates handover to a target cell (target eNodeB) that is not known by the source eNodeB, that is, no mapping from reported PCI to E-UTRAN cell global identifier (ECGI) exists, without ANR activated the source eNodeB rejects the handover attempt. With ANR this mapping can be verified by eNodeB ordering the UE (that reported the unknown PCI) to decode the ECGI from the target cell and reporting that to the source eNodeB. Therefore, the handover decision success rate is improved from around 60% to below 90% when ANR is activated as shown in Figure 12.35. Allowing ANR feature to add all measured cells by UE as neighbours will not be optimal. Having too many adjacent cells as neighbours may lead to a situation where radio conditions for handover target cells are not optimum for handovers to be successful, for example, minimum radio conditions are fulfilled in limited area or duration only. Therefore, the ANR feature use needs to be limited. This can be observed from Figure 12.36. As it can be seen right after the ANR feature was enabled the handover decision success rate improved a lot but the handover execution success rate did not improve enough. Therefore, after ANR was enabled and it added several neighbours some of the neighbours were deleted (or blacklisted) based on handover attempts statistics. This caused the handover decision success rate to decrease but at the same time the handover execution success rate improved further. It should be noted that ANR can easily add neighbours which are extremely far away from the reporting UE but just happen to provide very good coverage for certain location, for example, high-rise building, but then the handover execution can simply fail due to the random access preamble configuration (random access preamble cyclic shift length is too small). So at around day 180 further neighbour cell blacklisting was executed and handover decision success rate degraded further but at the LTE Key Performance Indicator Optimization Handover execution success 