 impact on Cell 1 CQI the physical layer optimization actions can be targeted to cells 3, B, C and E whose slope was between -0.53 to -0.95 compared to others ranging from -0.45 to -0.02. Drive testing can be conducted for coverage verification. In typical cluster optimization cases only downtilts are needed to be optimized. Example of physical layer optimization improvement (for 10 MHz FD LTE deployment) in terms of drive test is shown in Figure 12.7. y = -0.528x + 11.92 Downlink data volume (GB/hour) - cell 3 Figure 12.3 Interference caused by Cell 3 to Cell 1 = -0.906x + 12.04 Downlink data volume (GB/hour) - cell B Figure 12.4 Interference caused by Cell B to Cell 1 -0.953x + 11.96 Downlink data volume (GB/hour) - cell C Figure 12.5 Interference caused by Cell C to Cell 1 -0.630x + 11.98 Downlink data volume (GB/hour) - cell E Figure 12.6 Interference caused by Cell E to Cell 1 LTE Small Cell Optimization Drive test result Diff. (antenna tilting) Experienced improvement DL throughput 5 Mbps Handover attempts Average SINR 2.3 dB Average CQI Figure 12.7 Performance improvement in a cluster based on drive test results before and after changes (10 MHz bandwidth FD LTE deployment) Physical layer optimization impact on the KPI values is shown in the following sections. 12.4 Call Setup The call setup signalling is shown in Figure 12.8. It should be noted that some of non-access stratum (NAS) messages and security messages are omitted. The downlink control information (DCI) formats indicated in Figure 12.8 are according to [1]. The call setup signalling is initiated by the UE that is in RRC_IDLE state (no signalling connection with the network) due to received paging message or due to the NAS procedure initiated by the higher layers in the UE. The NAS message transmission or paging response transmission triggers the RRC connection setup procedure. The RRC connection setup proce- dure is the signalling connection establishment between the UE and the eNodeB enabling the E-RAB setup signalling for requested service. The