As large energy consumers, base stations need energy-efficient wireless access networks. An advanced energy efficiency measure was developed in this paper, considering throughput, the number of served users, and actual coverage area. The actual coverage area considered in the proposed measure is also in harmony with the measured network coverage area proposed by ETSI ES 203 228 V1.1.1 standard [1] which has been published by 3GPP. It is emphasized by 3GPP that to evaluate the actual coverage area, coverage probability should be taken into account in relation to the quality of service (QoS) definitions. However, coverage probability is not considered in all of the existing measurement methods. Hence, the developed measure turns out to be more effective than them as shown from the analysis and simulation results. Based on the developed measure, energy efficiency of Round Robin (RR) and Maximum SINR (MSINR) scheduling strategies for fractional frequency reuse (FFR) Schemes in orthogonal frequency division multiple access (OFDMA) Cellular Networks was investigated through closed-form expressions. The optimal power threshold of a base station (BS) and the optimal distance threshold of a cell were obtained from the results and the optimal distance threshold of MSINR is higher than that of RR while the optimal power threshold is not affected by scheduling strategies. Simulation also demonstrates that energy efficiency increases and the optimal distance threshold decreases with the number of users. However, the number of users has little impact on the optimal power threshold.

Fractional frequency reuse (FFR) is an efficient management technique to eliminate inter-cell interference (ICI) in multi-cell orthogonal frequency division multiple access (OFDMA) networks through inter-cell coordination. Generally, the derivations of throughput and coverage probability are treated as separate problems or investigated in different ways. In this paper, we derive average cell throughput and coverage probability expression for both round robin (RR) and maximum SINR (MSINR) scheduling strategies with different subcarrier allocation schemes from the same starting-point, the cumulative distribution function (CDF) of the instantaneous SINR . Results of static and dynamic subcarrier allocation schemes are compared to verify that latter is more reasonable because it takes both throughput and fairness into consideration. Analytical and simulation results also show that average cell throughput increases and coverage probability decreases with the distance threshold. Based on this, we investigate the optimal distance threshold to attain as good balances between throughput and coverage with different number of users in a cell. In terms of base station (BS) power control, we demonstrate that there exists an optimal power to satisfy coverage probability and obtain maximum throughput no matter what scheduling strategy is applied.

Inter-Cell Interference (ICI) is always a key problem in Fractional Frequency Reuse (FFR) system to be focused on, which should be well resolved to pursue higher throughput and better power efficiency. In this paper, we investigate throughput and power efficiency of RR scheduling in FFR system by both closed-form expression and Monte Carlo trials method. We improve a previous throughput model by applying variable subcarrier distribution scheme and upgrading expression for the Cumulative Distribution Function (CDF) of SINR. Then we propose a new closed-form expression of average cell throughput. The fairness performance of this model is better than that using fixed subcarrier distribution scheme. Meanwhile, an optimal radius threshold is selected so as to achieve best throughput performance. Then we manage to explore the relationship between cell power efficiency and transmit power based on the optimal radius threshold. From both analytical and simulation results, it is shown that power efficiency is monotonically decreasing with transmit power. Hence operational power is introduced into power efficiency as energy consumption for base station. After that, the highest power efficiency can be reached by setting a proper and reasonable transmit power.