Praise for Fundamentals of WiMAX

12.3 System-Level Simulation Results 419Table 12.6 Average Throughput per Sector for Band AMC with PF and RR SchedulersPed BPed ADL (Mbps) UL (Mbps) DL (Mbps) UL (Mbps)Proportional-fairness scheduler 14.61 2.35 15.54 2.50Round-robin scheduler 11.96 1.92 12.66 2.04receive diversity and transmit diversity improve the average throughput of a WiMAX network.By increasing the number of transmit antennas from two to four, the per sector throughputimproves by 50 percent. Similarly, by increasing the number of receive antennas from two tofour, the per sector throughput is increased by 80 percent. However, based on Figure 12.11 andFigure 12.12, it is evident that for the basic 2 × 2 open-loop configuration, the fifth and tenthpercentile DL data rates are not improved by increasing either transmit or receive diversity order.Thus, one can conclude that transmit diversity with antennas in DL is not sufficient to improvethe cell-edge data rate in the case of (1,1,3) reuse. Although receive diversity with four antennassomewhat improves the tenth percentile data rate, it is still not sufficient to improve the cell-edgedata rate when (1,1,3) frequency reuse is implemented.However, when closed-loop MIMO with four antennas at the BS is used, the per sector throughputand the fifth and tenth percentile data rates are significantly improved. The average per sectorthroughput is improved by 130 percent, and the cell-edge data rate per subchannel is highenough to provide reliable broadband services.Clearly, the 4 × 2 closed-loop MIMO feature provides significant improvement in the persector throughput and percentile data rates, compared to both the open-loop 2 × 4 and open-loop4 × 2 MIMO modes, because the transmitter is able to choose the optimum precoding matrix orbeamforming vector, in order to increase the link throughput. In this case, we assume that a singleprecoding matrix or beamforming vector is chosen for each 2 × 3 band AMC subchannel. 5The DL simulation results shown in Figure 12.9–Figure 12.12 assume that feedback for thequantized MIMO channel is provided by the receiver once every frame (5msec). (See Section8.9 for the quantized channel-feedback-based closed-loop MIMO solution). The UL enhancedconfiguration 3 uses a 2 × 4 open-loop MIMO. The increased performance over other enhancedprofiles comes from increasing the number transmit antennas in the UL from one to two. TheUL throughput results do not account for the fact that a part of the UL bandwidth is used by theclosed-loop MIMO feedback.Table 12.7 and Table 12.8 show the average throughputs per cell site and the percentile datarates for the various profiles. The biggest impact of the closed-loop MIMO appears to be on thepercentile data rate (Table 12.8). Based on the system-level performance of a WiMAX network,one can conclude that a (1,1,3) frequency reuse will not be able to provide carrier-grade reliabilityand guaranteed data rate unless closed-loop MIMO features of IEEE 802.16e-2005 are used.5. See Chapter 9 for a more detailed description of the band AMC subcarrier permutation mode.