Jan Garcia-Morales

Analytical Performance Evaluation of OFDMA-Based Heterogeneous Cellular Networks Using FFR

Two-tier wireless architectures where the macro- cellular network is complemented with a deployment of femto-cells are becoming an attractive solution to increase the global throughput in the context of OFDMA-based 4G/5G networks. This paper presents an analytical framework allowing the performance evaluation of FFR-aided OFDMA-based two-tier HetNets. A worst-case scenario in terms of inter- tier interference is evaluated in which macrocell and femtocell tiers are assumed to be uncoordinated and co-channel deployed. The proposed framework allows the evaluation of the impact produced by both inter- and co-tier interferences on either the macro-user-equipments (MUEs) or the femto-user-equipments (FUEs). Analytical performance results are used to optimise the FFR parameters as a function of, for instance, the resource block scheduling policy used at both the MBSs and the FBSs, the number of MUEs per cell, the density of FBSs per area unit or the degree of isolation provided by wall penetration losses.

Analysis and Optimization of FFR-Aided OFDMA-Based Heterogeneous Cellular Networks

Two-tier networks combining an operator-managed infrastructure of macrocell base stations combined with a user-deployed network of femtocells have recently emerged in the context of modern wireless standards as a solution to meet the ambitious performance requirements envisaged in 4G/5G architectures. Most often, these systems require interference coordination schemes that allow near universal frequency reuse while maintaining a considerably high signal-to-interference-plus-noise ratio levels across the coverage area. In particular, fractional frequency reuse (FFR) and its variants are deemed to play a fundamental role in the next generation of cellular systems. This paper develops an analytical framework targeting the downlink performance evaluation of FFR-aided orthogonal frequency division multiple access-based two-tier heterogeneous networks. In the considered scenario, macrocell and femtocell tiers are assumed to be uncoordinated and co-channel deployed, thus representing a worst-case scenario in terms of inter-tier interference. The proposed framework allows the evaluation of the impact produced by both inter- and co-tier interferences on the performance of either the macro-users (MUs) or the femto-users. Analytical results are used to optimize the FFR parameters as a function of, for example, the density of MUs per cell, the resource block scheduling policy, the density of femto base stations per area unit, or the degree of isolation provided by wall penetration losses. Moreover, different optimization designs of the FFR component are proposed that allow a tradeoff between throughput performance and fairness by suitably dimensioning the FFR inner and outer areas and the corresponding frequency allocation.

On the analysis of channel-aware schedulers in OFDMA-based networks using FFR

Interference coordination techniques are typically incorporated in OFDMA-based multi-cellular networks in order to preserve high spectral efficiencies over the whole coverage area and to improve the system capacity. Fractional frequency reuse (FFR) and its variants are employed to mitigate the inter-cell interference that particularly suffer cell-edge users. This paper presents an analytical framework that is used to optimise the FFR parameters in OFDMA networks when using channel-aware scheduling policies. The downlink performance evaluation results are obtained as a function of, for instance, the resource block scheduling policy or the density of UEs per cell. Furthermore, different optimisation designs of the FFR component are proposed that allow a tradeoff between throughput performance and fairness by suitably dimensioning the FFR inner and outer areas and the corresponding frequency allocation to each of these regions.

Channel-Aware Scheduling in FFR-Aided OFDMA-Based Heterogeneous Cellular Networks

In the context of OFDMA-based 4G/5G heterogeneous cellular networks, the deployment of femtocells is a solution to increase the capacity and coverage of indoor areas. This paper presents an analytical framework allowing the downlink performance evaluation of fractional frequency reuse (FFR)-aided OFDMA-based two-tier HetNets where scheduling of both macro and femto users takes into account user fairness and channel state information. The femtocell tier is assumed to be uncoordinated and co-channel deployed over the macrocells. Due to the use of interference coordination schemes in combination with channel-aware scheduling policies, a high spectral efficiency is preserved over the whole coverage area. The proposed framework allows the performance evaluation of the resource block scheduling policy on both the macro-and femto-tier taking into account the impact produced by the inter-and co-tier interferences. The average throughput results are given as a function of, for instance, the distance threshold that separates the macrocell-centre from the edge, the average number of user equipments per cell, the density of FBSs per area unit and the degree of isolation provided by wall penetration losses.

Performance Analysis and Optimisation of FFR-Aided OFDMA Networks using Channel-Aware Scheduling

Modern cellular standards typically incorporate interference coordination schemes allowing near universal frequency reuse while preserving reasonably high spectral efficiencies over the whole coverage area. In particular, fractional frequency reuse (FFR) and its variants are deemed to play a fundamental role in the next generation of cellular deployments (B4G/5G systems). This paper presents an analytical framework allowing the downlink performance evaluation of FFR-aided OFDMA networks when using channel-aware scheduling policies. Remarkably, the framework contemplates the use of different rate allocation strategies, thus allowing to assess the network behaviour under ideal (capacity-based) or realistic (throughput-based) conditions. Analytical performance results are used to optimise the FFR parameters as a function of, for instance, the resource block scheduling policy or the density of UEs per cell. Furthermore, different optimisation designs of the FFR component are proposed that allow a tradeoff between throughput performance and fairness by suitably dimensioning the FFR-defined cell-centre and cell-edge areas and the corresponding frequency allocation to each region. Numerical results serve to confirm the accuracy of the proposed analytical model while providing insight on how the different parameters and designs affect network performance.

Statistical Analysis and Optimization of a Fifth-Percentile User Rate Constrained Design for FFR/SFR-Aided OFDMA-Based Cellular Networks

Interference mitigation strategies are deemed to play a key role in the context of the next generation (B4G/5G) of multicellular networks based on orthogonal frequency division multiple access. Fractional and soft frequency reuse (FFR, SFR) constitute two powerful mechanisms for intercell interference coordination that have been already adopted by emerging cellular deployments as an efficient way to improve the throughput performance perceived by cell-edge users. This paper presents a novel optimal fifth-percentile user rate constrained design for FFR/SFR-based networks that, by appropriately dimensioning the center and edge regions of the cell, rightly splitting the available bandwidth among these two areas while assigning the corresponding transmit power, allows a tradeoff between cell throughput performance and fairness to be established. To this end, both the cumulative distribution function of the user throughput and the average spectral efficiency of the system are derived assuming the use of the ubiquitous proportional fair scheduling policy. The mathematical framework is then used to obtain numerical results showing that the novel proposed design clearly outperforms previous schemes in terms of throughput fairness control due to a more rational compromise between average cell throughput and cell-edge ICIC.

Multi-Layer FFR-Aided OFDMA-Based Networks Using Channel-Aware Schedulers

In orthogonal frequency-division multiple access (OFDMA) networks, the use of universal frequency reuse improves overall cell capacity at the cost of very high levels of inter-cell interference particularly affecting the users located in the cell-edge regions. In order to provide a better quality of experience to cell-edge users while still achieving high spectral efficiencies, conventional fractional frequency reuse (FFR) schemes split the cells into inner and outer regions (or layers) and allocate disjoint frequency resources to each of these regions by applying higher frequency reuse factors to the outer regions. Recently, multi-layer FFR-aided OFDMA-based designs, splitting the cell into inner, middle, and outer layers, have been proposed with the aim of further improving the throughput fairness among users. This paper presents an analytical framework allowing the performance evaluation and optimization of multi-layer FFR-aided OFDMA-based networks. Tractable mathematical expressions of the average spectral efficiency are derived and used to pose optimization problems allowing network designers to achieve the optimal trade-off between spectral efficiency and fairness. Analytical and simulation results clearly show that, irrespective of the channel-aware scheduler in use, multi-layer FFR-schemes can outperform the conventional two-layer FFR architectures.

FFR-aided OFDMA-based networks under spatially correlated shadowing

One of the most important factors affecting the quality of service (QoS) in orthogonal frequency division multiple access (OFDMA) networks is the intercell interference (ICI). An efficient technique for mitigating ICI is the well-known fractional frequency reuse (FFR), wherein cells are partitioned into center and edge spatial regions and different frequency reuse factors are applied to both of them. This work presents an analytical characterization of FFR-aided OFDMA-based networks that, unlike most previous studies, incorporates shadowing effects. The FFR design parameters maximizing the overall cell spectral efficiency, are determined for both round robin (RR) and maximum signal to interference plus noise ratio (MSINR) scheduling policies. Simulation results serve to validate the accuracy of the introduced model while at the same time reveal which are the optimum FFR settings.

Throughput Analysis and Optimization of Multi-layer FFR-aided OFDMA Networks

In OFDMA networks, the use of universal frequency reuse plans improves cell capacity but causes very high levels of inter-cell interference (ICI), particularly affecting users located in the cell-edge regions.In order to mitigate ICI while achieving high spectral efficiencies, fractional frequency reuse (FFR) shows a good tradeoff between cell-edge throughput and overall cell spectral efficiency.Recently, multi-layer FFR-aided OFDMA-based designs, splitting the cell into inner, middle and outer layers have been proposed and studied with the aim of increasing the spectrum utilization and improving the user fairness throughout the cell.This paper presents an analytical framework allowing the performance evaluation and optimization of multi-layer FFR designs in OFDMA-based networks.Tractable mathematical expressions of the average cell throughput as well as the layer spectral efficiency have been derived for both proportional fair (PF) and round robin (RR) scheduling policies.

Characterizing and optimizing the throughput of FFR/SFR-aided OFDMA networks

OFDMA-based multi-cellular standards incorporate interference coordination techniques that allow near universal frequency reuse while preserving reasonably high spectral efficiencies. In particular, frequency reuse approaches are employed to mitigate the inter-cell interference and thereby enhancing cell-edge users performance. Two representative strategies are fractional frequency reuse (FFR) and soft frequency reuse (SFR), which are deemed to play a key role in the next generation of cellular networks. This paper introduces an analytical framework allowing the analytical evaluation of performance metrics such as the spectral efficiency or user throughput CDF in the context of FFR/SFR-aided OFDMA networks. Remarkably, the proposed analytical framework is used to design optimal schemes by suitably dimensioning the inner and outer cellular areas, the frequency allocation to each of these regions and the corresponding transmit power. The performance evaluation results combine metrics such as spectral efficiency and the 5th-percentile of users rate in order to characterize and optimize the performance of FFR/SFR-aided OFDMA networks.