System Level Modeling and Optimization of the LTE Downlink

5. Performance Evaluation of Fractional Frequency Reuse in LTEFigure 5.2 shows example results for the FFR configuration employing β FR = 0.75and Γ thr = 3.20 dB FFR configuration. As presented in [133], this configuration wasfound to maximize capacity density and resulted in an improvement compared tothe reuse-1 case of: 8.68 % in terms of average performance, 61.81 % in edge capacitydensity, and 5.21 % in peak capacity density. As the focus of this thesis is on L2Smodeling, the details on the previous work regarding the optimization of capacitydensity have been excluded from this chapter. However, the obtained results, whichemploy a β FR -dependent SINR threshold, are shown in Figure 5.3.capacity density gain over reuse−1 [%]120100806040200−20reuse-1 referencemaximum :+61.85%+8.68%+5.21%−400 0.2 0.4 0.6 0.8 1(edge)(peak)Figure 5.3: FFR mean, edge, and peak capacity density gains relative to reuse-1 [133].As seen in Figure 5.3, FFR can potentially be employed to simultaneously boostmean, edge, and peak throughput. However, results were based on capacity calculations,and not actual throughput. Furthermore, a homogeneous distribution ofPHY resources was assumed, which may not be the case in a more realistic network,where typically proportional fair scheduling would be employed. In the remainingof this chapter, LTE FFR performance is analyzed in terms of throughput by meansof LTE system level simulations, concluding that when combined with scheduling,FFR provides no tangible additional gains in terms of optimum performance.5.3. System ModelPerformance has been evaluated for a 4 × 4 MIMO antenna configuration employingCLSM. In order to be able to evaluate the complete space of FFR configurations,an exhaustive search over all possible FFR configurations has been performed. Theconfiguration parameters taken into consideration are as follows:ˆ Bandwidth partitioning β FR : values from reuse-1 (β FR = 1) to practically reuse-3 (β FR = 0.01). As the frequency partitioning in LTE is based on RBs, theβ FR frequency allocation is constrained to allocate an integer and zero-modulo-68