System Level Modeling and Optimization of the LTE Downlink

5. Performance Evaluation of Fractional Frequency Reuse in LTE1.8(i)(i)Edge throughput [Mbit/s]1.61.41.210.80.6opt. RR fairnesstrade-offopt. PF fairnesstrade-off(ii)2.5 3 3.5 4 4.5Mean throughput [Mb/s](ii)Peak throughput [Mbit/s]98765opt. RR fairness trade-off(i)opt. PF fairness trade-off(i)(ii)(ii)4round robin schedulingproportional fair scheduling2.5 3 3.5 4 4.5Mean throughput [Mb/s]Figure 5.14: Edge (top) and peak (bottom) UE throughput vs. mean UE throughput: roundrobin and proportional fair scheduling.In Figure 5.14, analogous plots are shown for the relationship of the mean UEthroughput vs. edge and peak UE throughput, respectively. As expected fromthe relationship imposed between mean, edge, and peak throughput by the fairnessconstraint, the same effects observed in the results shown in Figure 5.13 are observedin Figure 5.14.The most desirable situation would be that of a “free” gain also for the proportionalfair scheduler, where the throughput accomplished in target (i) is higher than thatof the reuse-1 case or when in (ii), higher fairness values can be achieved withoutdecreasing throughput. However, as seen from the results in Figures 5.13 and 5.14,this is not possible.While 30 UEs per cell can be considered a big enough number to be consideredanalogous to a continuous distribution, it is also necessary to evaluate the performanceof FFR in less loaded situations. To this effect, for the optimum trade-offpoints listed as (i) (maximum fairness) and (ii) (maximum throughput without fair-78