d target block error ratio of transport blocks for first transmission = 10% taken on 12 seconds intervals. Figure 14.39 shows the results without TTI bundling (TTI bundling explained in Section 14.4.2) and Figure 14.40 shows the results with TTI bundling. The laboratory testing in Figure 14.39 shows how the PUSCH HARQ BLER rapidly increases when RSRP decreases to around -114 dBm level. POLQA MOS decreases after PUSCH BLER increase when the path loss is further increased and RSRP falls to around -116 dBm level (-119dBm without 3 dB RS boosting). The 70% PUSCH BLER is reached at about Successful SRVCC Failed SRVCC -130-125-120-115-110-105-100 -95 -90 -85 -80 -75 -70 -65 Target RSCP (dBm) Figure 14.41 Successful and failed SRVCC attempts as a function of WCDMA CPICH Ec/No and CPICH RSCP. Used fading channel is enhanced pedestrian A (EPA) with 3 km/h UE velocity. Used AMR codec bitrate = 12.65 kbps in LTE and 5.9 kbps in WCDMA VoLTE Optimization RSRP -120 dBm (~-123 dBm without RS boosting) which is similar result as indicated in the measurement results in Section 14.4.2. As can be seen from Figure 14.40 the TTI bundling greatly helps to maintain the voice quality (POLQA MOS) and PUSCH HARQ BLER until about -118 dBm (-121 dBm without 3 dB RS boosting) RSRP level, that is, performance gain from TTI bundling is around 2-3 dB. Also Figure 14.40 indicates that the SRVCC should be triggered latest at around -118 dBm (-121 dBm without 3 dB RS boosting) RSRP level in order to maintain the voice quality. The target system measurements should be started couple of decibels earlier (from RSRP point of view) at around -115 dBm (-118 dBm without 3 dB RS boosting) RSRP level in order to guarantee fast delivery of measurements (PUSCH HARQ BLER still <30%). The field and laboratory measurements of SRVCC handover to WCDMA have indicated that SRVCC failure rate increases rapidly once the target WCDMA common pilot channel (CPICH) Ec/NO falls below -16 dB with varying target CPICH RSCP conditions. The results of the testing as shown in 