-17) The (normalized) user throughput is defined as the average user throughput, i.e., the number of correctly received bits by users delivered to upper layers at the MAC SAP over a certain period of time, divided by the channel bandwidth and is measured in bits/s/Hz. The cell edge user spectral efficiency is defined as 5% point of the cumulative distribution function of the normalized user throughput. Let di, Ti, and B denote the number of correctly received bits by user i, the active session time for user i, and the channel bandwidth, respectively. The (normalized) user throughput of user i, is defined as: (12-18) The cell spectral efficiency and cell edge user spectral efficiency of IEEE 802.16m have been evaluated based on system-level simulations, and the results are shown in Table 12-9. It is shown that the IEEE 802.16 exceeds the IMT-Advanced requirements by a large margin. 12.9 IEEE 802. 16m link-level and system-level performance TABLE 12-9 IEEE 802. 16m Cell Spectral Efficiency and Cell Edge User Spectral Efficiency [2] Test Environments Duplex Requirements Scheme DL/UL Cell spectral efficiency (bits/s/Hz/cell) ITU-R requirement Cell edge user spectral 0.260 0.092 0.069 0.093 efficiency (bits/s/Hz) 0.075 ITU-R requirement Cell spectral efficiency (bits/s/Hz/cell) ITU-R requirement Cell edge user spectral 0.253 0.097 0.069 0.091 efficiency (bits/s/Hz) 0.075 ITU-R requirement Cell spectral efficiency (bits/s/Hz/cell) ITU-R requirement Cell edge user spectral 0.426 0.111 0.109 0.119 efficiency (bits/s/Hz) 0.015 ITU-R requirement Cell spectral efficiency (bits/s/Hz/cell) ITU-R requirement Cell edge user spectral 0.444 0.119 0.114 0.124 efficiency (bits/s/Hz) 0.015 ITU-R requirement 12.9.2 VolP Capacity While most of the modern packet-switched air interface systems do not specify voice codecs, the calculation of VoIP capacity requires explicit assumptions about a particular voice codec and its parameters, such the frame rate, RTP payload size, DTX capability, etc. The VoIP capacity of the IEEE 802.16m was ca