capacity drops by roughly 20% when going from 3 km/h to 30 km/h, and with higher velocity the capacity drops even further. This is because the radio channel is changing more rapidly and scheduling is thus more challenging. Moreover, the number of han- dovers is increased significantly when UE velocity increases. The results show that the handover delay is critical to the performance of VoIP service over HSDPA, especially when the UE velocity gets higher. This is caused by the fact that with high UE velocities the performance is already greatly affected by the radio channel conditions, and thus it is required to have fast response to the handover procedures. 10.7.2 LTE 10.7.2.1 Simulation Methodology and Assumptions The performance evaluation for LTE is conducted with a quasi-static system level simulator [11]. The simulated network is composed of 19 cell sites with 3 sectors each. The scheduling algorithm and other radio resource management (RRM) © 2009 by Taylor & Francis Group, LLC Radio Access Network VolP Optimization Table 10.6 Summary of Main Simulation Parameters Description Settings Number of cells 19 Sites with 3 cells Carrier center frequency 2.0 GHz Simulation scenarios Macro case 1 and macro case 3 System bandwidth 5 MHz Path loss According to [27], minimum coupling loss (MCL) 70 dB Standard of log-normal shadowing Velocity 3 km/h Channel SCM-C with correlations for spatial channels Link to system model DL EESM (realistic ChEst), UL AVI (realistic ChEst) PDCCH modeling Realistic functions are explicitly modeled in 3 center cells, and statistics are also gathered from these 3 center cells. The remaining cells generate intercell interference with full load. The propagation characteristics of the physical link as a distance depen- dent path loss, shadowing and frequency selective fast fading are modeled in the system simulator, whereas the link performance is fed to the system simulator through an Exponential Effective SNR Mapping (EESM) interface [25] or, alterna- tively, through an Actual Value Interfa