rer setup challenges are not considered. The E-RAB setup success rate is only marginally impacted by the increase in traffic (and inter-cell interference) compared to random access setup success rate and RRC connection setup success rate as can be seen from Figure 12.19. The RB setup LTE Small Cell Optimization Evolved-UTRAN Evolved packet core Internet End-to-end service Evolved packet system bearer External bearer E-UTRAN radio access bearer S5/S8 bearer Radio bearer S bearer Radio S5/S8 Figure 12.18 LTE bearer architecture [3] success rate in Figure 12.19 also includes incoming handovers (HO) for which the RB is established in the target cell whereas the E-RAB setup success rate does not contain any HO scenarios hence the difference. The increased inter-cell interference causes RRC connection reconfiguration message decoding challenges in the UE and RRC connection reconfiguration complete message decoding challenges in the eNodeB. E-RAB setup success rate improvement after parameter optimization (explained below) is shown in Figure 12.20. RRC connection setup success rate RB setup success rate E-RAB setup success rate Random access setup success rate Day 1 Day 2 Day 3 Figure 12.19 Average E-RAB setup success rate, radio bearer (RB) setup success rate, RRC connection setup success rate and random access setup success rate per cell in a cluster during moderate traffic (15 minutes statistics collection period) LTE Key Performance Indicator Optimization E-RAB setup success rate (%) Figure 12.20 Average E-RAB setup success rate improvement after parameter optimization for coverage-limited cluster, day-level statistics The improvement in E-RAB setup success rate after day 31 comes from link adaptation parameter optimization. This includes minimum resource allocation size optimization together with UE transmission power control for coverage-limited scenarios, that is, minimizing the number of PRBs and MCS in order to minimize the UE transmission power while maximizing the E-RAB setup success rate. Figure 12.21 shows 