" IEEE VTC Spring, Singapore, May 2008.) © 2009 by Taylor & Francis Group, LLC Long Term Evolution: 3 GPP LTE Radio and Cellular Technology AMR 12.2 kbps Uplink Downlink WCDMA R99 CS HSPA R6 VolP HSPA R7 VolP LTE R8 Voice Figure 10.21 Voice capacity with WCDMA/HSPA/LTE. Mobility clearly degrades VoIP capacity. With high speed, the loss (compared to the case with the pedestrian speed of 3 km/h) is about 63%, SO the capacity is roughly only one-third of the nonmobility case. The loss in capacity is caused by several fac- tors: First, the CQI measurements become less accurate as the speed increases, which causes the scheduler to lose most of the efficiency of frequency-dependent schedul- ing. Link adaptation also performs badly as it is tied to the CQI reports, leading to an increase in retransmissions. And the faster the users move, the more handovers are done, with all the resulting effects (L1 packets flushed when a handover is done, delays due to handover execution delay) also affecting the VoIP capacity [43]. 10.7.3 VolP Performance Comparison between HSPA and LTE The voice capacity comparison among WCDMA, HSPA, and LTE is summarized in Figure 10.21 for 5 MHz bandwidth. From the comparison, it is obvious that HSPA Release 7 provides a clear improvement to the voice capacity compared to the CS voice. When comparing voice capacities between HSPA and LTE, it is observed that LTE achieves more than 100% higher capacity than HSPA Release 7. Furthermore, it can be noted that both VoIP capacity is UL limited in both HSPA and LTE. 10.8 Summary and Conclusion The potential for simplifications in the core network and the cost benefits that an "All IP network" can provide are clear. However, the VoIP solution has to work well to enable a stand-alone cellular system with all the commonly used services. © 2009 by Taylor & Francis Group, LLC Radio Access Network VolP Optimization The network has to be able to guarantee the same service quality and higher voice capacity with VoIP than has been required from CS-based voice sys