System Level Modeling and Optimization of the LTE Downlink

5. Performance Evaluation of Fractional Frequency Reuse in LTE5. Performance Evaluation of FractionalFrequency Reuse in LTEFractional Frequency Reuse (FFR) has been investigated as a method to combinethe peak spectral efficiency of a reuse-1 scheme and the edge spectral efficiency performanceof higher-order frequency reuse schemes [123] by simultaneously employingdifferent reuse factors within a cell. Ultimately, FFR aims at improving cell edgeperformance when compared to a reuse-1 scheme while maintaining cell center performance.Although LTE is a reuse-1 scheme, the use of OFDMA as the PHY layerin the standard enables easy implementation of frequency partitioning schemes suchas FFR.FFR performance is typically assessed in literature [124–131] by means of threeKey Performance Indicators (KPIs) derived from the throughput ecdf. These are (i)mean throughput, (ii) edge throughput, and (iii) peak throughput. Here, the terms“peak” and “edge” refer, as widely employed in literature, to the the 95% and 5%points of the UE throughput ecdf. These can be interpreted as the performance ofan UE at the cell center and at cell edge, respectively.Over the course of this chapter, an analysis of the achievable throughput improvementof applying FFR to LTE is performed and, based on the results, argued thatthe mean, edge, and peak throughput KPIs need to be combined with a fairnessmeasure [57] to suitably be able to quantify the trade-off between reuse-1 and thehigher-order reuse in FFR.65