. A fixed overhead model for the uplink control channels was used. The IEEE 802.16m VoIP capacity results in various test environments are given in Table 12-10. Since the downlink-to-uplink ratio is for the TDD and FDD modes, and from Table 12-8 the uplink control overhead is less than that of the downlink, the VoIP capacity in the uplink direction is higher than in the downlink direction; however, the system VoIP capacity is the least of the downlink and uplink capacities due to the symmetrical property of VoIP traffic. 12.9.3 Mobility Following the methodology for evaluation of the mobility requirement [6] in the first step, the system- level simulation was performed for each test environment in the uplink to obtain the uplink SINR distribution. From the uplink SINR distribution, the 50th percentile value was obtained for each test environment. In the second step, link-level simulation was run to generate the spectral efficiency versus SINR curves for each test environment. The spectral efficiency values included the effect of the control channel overhead from the uplink system-level simulations for each test environment. The 12.9 IEEE 802.16m link-level and system-level performance TABLE 12-10 IEEE 802.16m VolP Capacity in Various Test Scenarios [2] Downlink Uplink VolP System ITU-R VolP Capacity Capacity Capacity requirement Duplex (Active Users/ (Active Users/ (Active Users/ (Active Users/ Environment Scheme MHz/Cell) MHz/Cell) MHz/Cell) MHz/Cell) mobility requirement is met, if the spectral efficiency values from the link-level curves, obtained for the median SINR value from the system-level simulations, are greater than the target values. These values were obtained assuming an antenna configuration of 4 X 2 in the downlink and of 2 X 4 in the uplink. The statistical distribution of the uplink SINR for various test scenarios based on the IEEE 802.16m is simulated and is shown in Figure 12-8. The median uplink SINR is extracted from the distribution and is used in the calculation of the link-level spectral e