gets worse. There is room for optimization, but knowing that generally only small percentage of the calls experience one SRVCC and that 300 ms interruption is hardly noticeable, the performance is good for the purpose. SRVCC Success The purpose of SRVCC is to handover the VoLTE call to the target system, for example, WCDMA, before the LTE coverage runs out. Therefore, in order to guarantee sufficiently high VoLTE call quality the SRVCC must have very high success rate. The source (LTE) cell must have good enough coverage to deliver the necessary signalling between the UE and the eNodeB for measurements as well as for the handover execution command itself. The field and laboratory measurements of SRVCC handover to WCDMA have indicated that the MOS (POLQA) decreases rapidly when the LTE coverage runs out as well as the HARQ BLER increases rapidly indicating delays in successful PUSCH packet delivery from the UE. The laboratory measurements in Figures 14.39, 14.40 and 14.41 are done with enhanced pedestrian A fading channel 3 km/h UE velocity Doppler shift. The reference signal transmission power from eNodeB was boosted by 3 dB, eNodeB transmission power for 2 X 2 MIMO was set to 15 W+15 W and 10 MHz bandwidth was used. The used measurement tool averaged the UE-measured RSRP and PUSCH HARQ BLER over 1 second and the voice samples for the used 12.65 kbps wideband AMR codec for POLQA MOS evaluation were PUSCH BLER POLQA MOS Figure 14.39 Laboratory measurements of RSRP, PUSCH BLER and POLQA MOS without TTI bundling. Used fading channel is enhanced pedestrian A (EPA) with 3 km/h UE velocity and 3 dB reference signal boosting. Used AMR codec bitrate = 12.65 kbps and target block error ratio of transport blocks for first transmission = 10% LTE Small Cell Optimization PUSCH BLER POLQAMOS Figure 14.40 Laboratory measurements of RSRP, PUSCH BLER and POLQA MOS with TTI bundling. Used fading channel is enhanced pedestrian A (EPA) with 3 km/h UE velocity and 3 dB reference signal boosting. Used AMR codec bitrate = 12.65 kbps an