Analytical Evaluation of Throughput and Power Efficiency Using Fractional Frequency Reuse

With the growing concern over energy consumption, green communication is becoming more and more important. Lots of efforts have been put into investigating in energy-efficient wireless systems. Since Fractional Frequency Reuse (FFR) is a widely-used Inter-cell-interference coordination scheme in the OFDMA wireless network, we consider the energy-efficient power control in the FFR system. With demanded user rate constraints, we aim at minimizing the Joule consumed per transmission bit per-cell in the downlink. Based on Dinkelbach's theory, we transform the objective function into a parametric programming problem. By proving the problem is convex, we derive the optimal analytical solution by Karush-Kuhn-Tucker (KKT) conditions, along with an energy-efficient power control algorithm. Numerical results are given to verify our analysis, and demonstrate that the power control algorithm significantly improves the energy efficiency in FFR. The optimal frequency reuse factor is also given when considering the fairness of energy efficiency and power consumption.

The project to define Long Term Evolution (LTE) of UMTS cellular technology started in year 2004 is well established to the world. The subsequent evolve of LTE-Advanced however targets for enhancement in average spectrum efficiency and cell-edge user throughput. The limiting factor of the system performance at cell-edge is inter-cell interference (ICI). The challenge that is discussed in this paper focuses on ensuring the overall satisfaction mainly cell-edge system performance through the analysis on Fractional Frequency Reuse (FFR) and hybrid Macro system which involves small cell technology — Femtocell technology. This paper discussed the three frequency allocation schemes. The schemes include without the application of Femtocell, with randomly application of Femtocell and with preplanned Femtocell scheme. The FFR mechanism divides the cell into two regions (inner and outer). The inner radius and inner region resource is determined base on overall average throughput and overall user satisfaction.

Joint virtual edge-clustering and spectrum allocation scheme for uplink interference mitigation in C-RAN

Multiuser Orthogonal Frequency Division Multiple Access (OFDMA) networks, such as Long Term Evolution networks, use the frequency reuse-1 model to face the tremendous increase of mobile traffic demands, and to increase network capacity. However, inter-cell interference problems are generated, and they have a negative impact on cell-edge users performance. Resource and power allocation should be managed in a manner that alleviates the negative impact of inter-cell interference on system performance. In this paper, we formulate a novel centralized multi-cell resource and power allocation problem for multiuser OFDMA networks. The objective is to maximize system throughput while guaranteeing a proportional fair rate for all the users. We decompose the joint problem into two independent problems: a resource allocation problem and a power allocation problem. We prove that each of these problems is a convex optimization problem, and that their optimal solution is also an optimal solution to the original joint problem. Lagrange duality theory and subgradient projection method are used to solve the centralized power allocation problem. We study the convergence of our centralized approach, and we find out that it reduces inter-cell interference, and increases system throughput and spectral efficiency in comparison with the frequency reuse-1 model, reuse-3 model, fractional frequency reuse, and soft frequency reuse techniques.

In this work, the authors derive the optimal signal‐to‐interference‐ratio (SIR) thresholds S t which maximise coverage probability for both fractional frequency reuse (FFR) and soft frequency reuse (SFR) networks with base station locations modelled using Poisson point process. It is analytically shown that for both FFR and SFR, the optimal SIR threshold is equal to the target SIR T , i.e, S t = T . The authors also show that at the optimal SIR threshold, FFR achieves a higher coverage than frequency reuse (1/Δ). Furthermore, for the cases when S t > T and S t < T , FFR achieves a higher coverage than reuse (1/Δ) and reuse 1, respectively. On the other hand, SFR coverage can be higher or lower than reuse (1/Δ) coverage, even when S t = T . However, when S t > T , SFR achieves a higher coverage than reuse 1, and when S t < T , the SFR coverage can be lower than reuse 1 coverage. The FFR and SFR coverages are also compared for a given Δ, and it is shown that FFR achieves a higher coverage than SFR at the optimal value of S t .

In next generation wireless systems such as Long Term Evolution (LTE), Radio Resource Management with Inter-cell Interference Coordination (ICIC), is a key issue to be addressed. Although centralized resource allocation (RA) and collaborative processing can optimally perform ICIC, the overall required complexity suggests the consideration of distributed techniques. In this paper we investigate the behavior of distributed RA strategies aimed at maximizing the weighted average sum-rate of a multi-cell clustered system in presence of power constraints by evaluating throughput gap and fairness with respect to their respective centralized implementations. In the distributed RA strategies the inter-cell interference is partially coordinated through the use of power planning schemes (fractional frequency reuse - FFR - is the case considered here), leading to a reduction in both signaling and feedback requirements. The results obtained show that the distributed RA with aggressive frequency reuse is able to approach t performance of the centralized RA when the number of users is large. However, FFR is useful to improve fairness (or cell-edge user performance) at the expense of sum-rate when the scheduling weights are those of proportional fair scheduling (PFS), whereas FFR and in general power planning techniques are able to improve throughput while preserving the fairness when the scheduling weights are set to guarantee equal average rate to users.

Inter-Cell Interference Coordination (ICIC) using frequency reuse schemes in Orthogonal Frequency Division Multiple Access (OFDMA) cellular networks is one of the most promising approaches to reduce the effect of interference and to improve the system performance. Fractional Frequency Reuse (FFR) schemes are efficient interference mitigation techniques that have been used to improve system performance in multirelay multi-cell OFDMA cellular networks, especially for the cell edge users. The purpose of FFR design is to deploy frequency patterns (sets) in such a way that a Mobile Station (MS) user can reduce interference from adjacent cells. The Frequency Reuse Factor (FRF) of 7/3 with frequency reuse pattern (7, 3, 1) is used to improve the system performance of FRF=1 and FRF=3. This paper proposes a new frequency pattern and deploys frequency sets with Amplify and Forward (AF) fixed relays to improve the performance of the system. Simulation results show that the proposed pattern achieves significant Inter-Cell Interference (ICI) reduction when compared to other cooperative and noncooperative schemes.

Dynamic time-division duplex (D-TDD) has emerged as an effective solution to accommodate the unaligned downlink and uplink traffic in small cell networks. However, the flexibility of traffic configuration also introduces additional inter-cell interference. In this letter, we study the effectiveness of applying fractional frequency reuse (FFR) as an interference coordination technique for D-TDD small cell networks. We derive the analytical expressions of downlink and uplink mean packet throughput (MPT), then study a network parameter optimization problem to maximize MPT while guaranteeing each user's throughput. Numerical results corroborate the benefits of the proposed FFR-based D-TDD in terms of improving throughput.

For the upcoming 4G systems, network multiple-input multiple-output (MIMO) and inter-cell interference coordination (ICIC) are two of key techniques adopted in 4G systems to mitigate the serious inter-cell interference (ICI) and improve coverage and cell-edge throughput. Network MIMO is referred to as coordinated multi-point (CoMP) in LTE-A. In this paper, we propose a simulation platform to analyze the handover issue for downlink CoMP transmissions in LTE-A cellular systems. Among the variety of ICIC strategies, we apply the widely adopted soft frequency reuse (SFR) and the fractional frequency reuse (FFR) schemes. Both schemes are based on the idea of applying a frequency reuse factor of one in cell-center areas, and a higher reuse factor in cell-edge areas. Therefore, the ICI is reduced at the expense of the available frequency resources for each cell.

Introduction In conventional cellular systems, cochannel interference is a serious issue that degrades system performance. The spectral efficiency of cellular networks is fundamentally limited by the interference between cells and users sharing the same channel for both downlink and uplink. Generally, there are two kinds of cochannel interference: intracell interference and intercell interference. The intracell interference can be resolved by allocating orthogonal frequency resources. To mitigate intercell interference, there are several general approaches such as frequency reuse, cell sectoring, and spread spectrum transmission. The most commonly used technique is to avoid using the same set of frequencies in neighboring cells. This approach leads to the decrease of the number of available channels within each cell. Universal frequency reuse, i.e., reuse factor of 1, is preferred for future broadband wireless communications systems, such as the Third Generation Partnership Project (3GPP) long-term evolution (LTE) and worldwide interoperability for microwave access (WiMAX). In the orthogonal frequency-division multiple access (OFDMA) systems, which do not have processing gain as the code-division multiple access (CDMA) system, how to achieve the goal of both universal frequency reuse and reducing intercell interference is a key challenge. The concept of fractional frequency reuse (FFR) has been suggested to improve spectrum efficiency by applying reuse partition techniques, in which the inner region of the cell is assigned the whole frequency spectrum and the outer region is only assigned a small fraction of the frequency spectrum.

The severe interference in full-duplex (FD) cellular network largely degrade the system performance, especially for cell edge users. In this paper, hybrid full/half duplex cellular network which is composed of a mixture of FD and half duplex (HD) base-stations (BSs) is focused. In order to relieve the received inter-cell interference, frequency reuse (FR) is applied. The adopted FR schemes include traditional full FR and two kinds of fractional FR (FFR) named Strict FFR (StFFR) and Soft FFR (SoFFR). Stochastic geometry is adopted to evaluate the system performance. Tractable results of the ergodic rate and coverage probability for different FR schemes are obtained. Through the numerical results, we can observe that full FR and StFFR schemes can improve the user coverage probability at the expense of system spectrum efficiency (SE). SoFFR can improve both the coverage probability and the system SE. The numerical results also show that if the residual Self-interference is not very strong, operating all the BSs in FD mode can achieve the best performance, otherwise, it is better to operate all the BSs in HD mode.

With significant growth in portable multimedia devices such as smartphones, application processors (AP) play a critical role for running various multimedia applications on these devices. By considering the power constraints of such devices, we often integrate reconfigurable processors (RPs) into APs. This is because RPs offer flexibility and good performance, thereby greatly improving the power efficiency for running these multimedia applications. Like many other processors, RPs also exploit the dynamic voltage/frequency scaling (DVFS) to improve their power efficiency. Owing to the platform cost constraints, however, these RPs are often integrated to low dropout (LDO) voltage regulators (VRs) instead of switching VRs. When compared with switching VRs, LDO VRs are very inexpensive; however, they suffer from considerable power loss when they are required to deliver a low output voltage. However, many previous studies focused on analyzing the power efficiency of various DVFS techniques only with regard to the processors and did not consider the negative impact of the VR power losses on the overall power efficiency of the platform. In this work, we quantitatively compare the power efficiency of a Samsung RP (SRP) adopting the race-to-halt technique with that of the SRP exploiting the DVFS supported by LDO VRs, by considering the effect of the VR power losses. Finally, we demonstrate that using the race-to-halt technique results in high power efficiency when compared with the DVFS in a commercial processor, by considering the VR power efficiency.

In this paper, we propose a combined analytical and simulation framework for performance evaluation of the forward link in the cdma2000 evolution for data only (1xEV‐DO) cellular systems with throughput and spectral efficiency being used as performance metrics. A closed form expression for the aggregate average throughput is derived in terms of system‐dependent parameters and a discrete random process that reflects the stochastic behavior of the transmission channel. The random process is expressed in terms of the cumulative distribution function (CDF) of the users signal‐to‐interference‐plus‐noise ratio (SINR). Quantitative results for throughput and spectral efficiency are presented for a variety of users distribution models, base station antenna types and frequency reuse factors for the cases of sectorized and non‐sectorized cells. Furthermore, we study the impact of the cell radius on the system performance. Copyright © 2006 John Wiley & Sons, Ltd.

Intercell interference (ICI) is one of the major factors that limit the performance of wireless cellular network systems. Soft frequency reuse (SFR) as well as its modified algorithms such as Soft fractional frequency reuse (Soft FFR) and Distributed fractional frequency reuse (Distributed FFR) have been introduced as an effective way to optimize spectrum and control the ICI. However, the comparison between these algorithms has not fully been presented by the researchers proposing the models. This paper presents a comparison of the performance of well-known frequency reuse algorithms in term of system throughput, average packet loss ratio and average packet delay. The simulation results indicate that the simplest scheme, i.e. Soft FR, archives the highest system performance comparing to Soft FFR and Distributed FFR. Hence, it is noticed that one of the effective methods which optimize frequency reuse is to reduce the algorithm complexity.

For the next generation wireless communication systems, inter-cell interference (ICI) is the primary cause of performance degradation in cell edge mobile stations of OFDMA multi-hop cellular networks with the frequency reuse pattern (1, 3, 1). This paper introduces a new fractional frequency reuse scheme to assign radio resources in OFDMA multi-hop networks to reduce inter-cell interference and maintain the sector frequency reuse factor at 1. Through the numerical analysis, we find that this scheme can yield higher SINR and improve the system capacity. Furthermore, the results also indicate that fractional frequency reuse relay system with local forwarding scheme can achieve higher throughput than local forwarding scheme in conventional relay system.