n Semi-persistent Dynamic Total number of CCEs in use per TTI Figure 10.19 Distribution of used CCEs per TTI. © 2009 by Taylor & Francis Group, LLC Radio Access Network VolP Optimization function of the used control channel elements (CCEs) per TTI. As control channel limitation becomes a bottleneck for VoIP UL system performance with fully dynamic PS, especially if a very high number of users are accessed into the system, that is, as is the case with AMR 7.95. Due to the control channel limitations, fully dynamic PS can support only 230 users per sector in Casel with AMR 7.95, whereas with semi-persistent scheduling, control channel limitations can be avoided and 320 users with a gain of 40% can be supported. However, with AMR 12.2, the impact of control channel limitations is much smaller for the fully dynamic PS due to bigger VoIP payload sizes and hence a smaller number of supported users at 5% outage. Therefore, the capacity gain of semi-persistent PS over fully dynamic PS is only about 14%. Finally, when comparing the performances of DL and UL together, it is con- cluded that the VoIP performance in LTE is UL limited, similar to HSPA. This is mainly due to the coverage limitation in UL, which is caused by the relatively low maximum transmit power of the UEs. The extra DL capacity is not wasted but can be used, for example, for supporting additional best effort traffic (web browsing, etc.), which is typically asymmetric and geared more toward DL. VolP performance with mobility in LTE Figure 10.20 shows the average behavior of different UE mobility scenarios in LTE. The simulations were run with dynamic scheduling, but it is assumed that similar behavior would result with semi-persistent scheduling. Average VolP capacity loss from mobility 30 km/h 120 km/h Speed Figure 10.20 Average VolP cell capacity with different UE velocities and han- dover delays. (Source: T. Henttonen, K. Aschan, J. Puttonen, N. Kolehmainen, P. Kela, M. Moisio, and J. Ojala, "Performance of VolP with mobility in UTRA long term evolution,