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It is well known that per macro-site spectral efficiency (SE) can be increased through higher order sectorization (HOS) by radially partitioning the coverage area of each site into multiple sectors and reusing the spectral resources in each sector and across all sites. In order to further reinforce its benefits, HOS can be combined with fractional frequency reuse (FFR) techniques to improve the SE and/or energy efficiency (EE) of the network. This paper presents an analytical framework that is used to assess the sectorization performance in terms of both the SE and EE in the downlink of HOS/FFR-aided orthogonal frequency-division multiple access (OFDMA)-based macro-cellular networks. Tractable mathematical expressions are derived for the round robin, the proportional fair, and the maximum signal-to-interference-plus-noise ratio scheduling rules and the corresponding capacities. The results show the impact of the sectorization gain on the system performance for different cell-edge frequency reuse factor values. Furthermore, an optimization problem for the HOS/FFR-aided OFDMA-based network is addressed, allowing a tradeoff between the EE performance and fairness by suitably dimensioning the FFR inner and outer areas and the corresponding frequency allocation to each of these regions.

In the last few years, multicast device-to-device (D2D) cellular networks has become a highly attractive area of research. However, a particularly challenging class of issues in this area is data traffic, which increases due to increase in video and audio streaming applications. Therefore, there is need for smart spectrum management policies. In this paper, we consider a fractional frequency reuse (FFR) technique which divides the whole spectrum into multiple sections and allows reusing of spectrum resources between the conventional cellular users and multicast D2D users in a non-orthogonal scenario. Since conventional cellular users and multicast D2D users shared same resources simultaneously, they generate severe data traffic and high communication overhead. To overcome these issues, in this paper we propose Lagrange relaxation technique to solve the non-convex problem and combinatorial auction-based matching algorithm to select the most desirable resource reuse partners by fulfilling the quality of service (QoS) requirements for both the conventional cellular users and multicast D2D users. Then, we formulate an optimization problem to maximize the overall system performance with least computational complexity. We demonstrate that our method can exploit a higher data rate, spectrum efficiency, traffic offload rate, coverage probability, and lower computational complexity.

Owing to its high capabilities in terms of spectral efficiency and flexibility, orthogonal frequency division multiple access (OFDMA) has played a crucial role towards the success of 4G cellular systems and an increasing number of actors in the 5G arena strongly advocate for its continuation. OFDMA-based architectures do not introduce intracell interference but, due to the use of very aggressive frequency reuse plans, they must implement some form of inter-cell interference (ICI) control to warrant prescribed levels of quality of service, specially to users located near the cell edge. An efficient technique for mitigating ICI in OFDMA networks is the well-known fractional frequency reuse (FFR) scheme. In FFR, a signal-to-interference-plus-noise ratio threshold is used to categorize mobile stations (MSs) as cell-center or cell-edge MSs. Furthermore, a different number of frequency resources are allocated to cell-center and cell-edge areas according to a prescribed frequency reuse plan. This paper presents an analytical characterization of FFR-aided OFDMA-based multi-cellular networks that, unlike most previous studies, incorporates shadowing effects and, furthermore, considers that base stations are irregularly deployed. This analytical approach can incorporate different scheduling rules and can underpin different designs for which the optimal FFR parameters can be derived. The proposed framework allows the performance evaluation and optimization of any cell in the system by considering the specific network topology, the user association and categorization processes, the spatial density of users and the characteristics of both the fast multipath fading and the spatially correlated slow shadow fading.

Device-to-device (D2D) communications can be adopted as a promising solution to attain high quality of service (QoS) for a network. However, D2D communications generates harmful interference when available resources are shared with traditional cellular users (CUs). In this paper, network architecture for the uplink resource management issue for D2D communications underlaying uplink cellular networks is proposed. We develop a fractional frequency reuse (FFR) technique to mitigate interference induced by D2D pairs (DPs) to CUs and mutual interference among DPs in a cell. Then, we formulate a sum throughput optimization problem to achieve the QoS requirements of the system. However, the computational complexity of the optimization problem is very high due to the exhaustive search for a global optimal solution. In order to reduce the complexity, we propose a greedy heuristic search algorithm for D2D communications so as to find a sub-optimal solution. Moreover, a binary power control scheme is proposed to enhance the system throughput by reducing overall interference. The performance of our proposed scheme is analyzed through extensive numerical analysis using Monte Carlo simulation. The results demonstrate that our proposed scheme provides significant improvement in system throughput with the lowest computational complexity.

Device-to-device (D2D) communication is affirmed as one of the dynamic techniques in improving the network throughput and capacity and reducing traffic load to the evolved Node B (eNB). In this paper, we propose a resource allocation and power control technique in which two-pairs of D2D users can simultaneously share same uplink cellular resource. In this case, interference between D2D users and cellular users is no longer insignificant so it must be properly handled. The proposed scheme considers fractional frequency reuse (FFR) scheme as a promising method that can relatively reduce the intra-cell interference. The main objective of the proposed scheme is to maximize the D2D communication throughput and overall system throughput by minimizing outage probability. Hence, we formulate an outage probability problem and overall system throughput optimization problem while guaranteeing minimum allowable signal-to-interference-plus-noise ratio (SINR). For fair distribution of cellular resources to multiple D2D pairs, we used Jain's fairness index (JFI) method. Simulation is conducted in MATLAB and our simulation results demonstrate that the proposed scheme achieves remarkable system performance as compared with existing methods.

Wireless multimedia sensor networks (WMSNs) have been improved with the increase of multimedia data. In WMSNs, a centralization problem can occur because of large-size multimedia data. It is necessary to consider device-to-device (D2D) communication. We focus on D2D WMSN based on cellular networks. Sensors in the D2D WMSN can non-orthogonally use a cellular link, which is a wireless communication channel between a sensor and an aggregator, and a D2D link, which is the channel between sensors. As a result, it has more complex interference environments than an ordinary system. Therefore, it is a key factor to manage the varying inter-cell interference effectively for throughput improvement. We propose an interference mitigation scheme that can be applied to D2D WMSN. In the proposed scheme, a cell is separated into six zones and orthogonal frequency is allocated to each zone for cellular links. The frequencies allocated to cellular links are reused by D2D links of neighboring zones. The simulation results show that the throughput of the proposed scheme increases two times compared to a static frequency allocation scheme.

International audience; Mobile network operators are facing the challenge to increase network capacity and satisfy the growth in data traffic demands. In this context, Long Term Evolution (LTE) networks, LTE-Advanced networks, and future mobile networks of the Fifth Generation seek to maximize spectrum profitability by choosing the frequency reuse-1 model. Due to this frequency usage model, advanced radio resource management and power allocation schemes are required to avoid the negative impact of interference on system performance. Some of these schemes modify resource allocation between network cells, while others adjust both resource and power allocation. In this article, we introduce a cooperative distributed interference management algorithm, where resource and power allocation decisions are jointly made by each cell in collaboration with its neighboring cells. Objectives sought are: increasing user satisfaction, improving system throughput, and increasing energy efficiency. The proposed technique is compared to the frequency reuse-1 model and to other state-of-the-art techniques under uniform and non-uniform user distributions and for different network loads. We address scenarios where throughput demands are homogeneous and non-homogeneous between network cells. System-level simulation results demonstrate that our technique succeeds in achieving the desired objectives under various user distributions and throughput demands.

We consider the downlink of a multicell system comprised of base stations (BSs) and user terminals equipped with multiple antennas respectively on the condition that arbitrary BS cooperation and distance dependent propagation path loss are assumed. In this paper, we consider homogeneous networks for the rectangular coordinates and show the cell edge performance of cellular networks based on distance from their cell center, i.e., BS. We focus on the downlink capacity of edge users in the cellular networks and show that BS cooperation can improve the spectral efficiency. The BSs cooperate for their transmission to the cell edge users in order to improve their signal-to-interference-plus-noise ratio (SINR) for inter-cell interference (ICI) cancelation in downlink multicell systems. When fractional frequency reuse (FFR) is applied to the cell edge, it is conjectured that BS cooperation, or a coordinated multipoint (CoMP), will further improve the system performance. Simulation results show that the proposed scheme outperforms the reference schemes in terms of the cell edge SINR with a minimal impact on the path loss exponent in the networks.

To handle the fast-growing demand for high data rate applications, the capacity of cellular networks should be reinforced. However, the available radio resources in cellular networks are scarce, and their formulation is expensive. The state-of-the art solution to this problem is a new local networking technology known as the device-to-device (D2D) communication. D2D communications have great capability in achieving outstanding performance by reusing the existing uplink cellular channel resources. In D2D communication, two devices in close proximity can communicate directly without traversing data traffic through the evolved-NodeB (eNB). This results in a reduced traffic load to the eNB, reduced end-to-end delay, and improved spectral efficiency and system performance. However, enabling D2D communication in an LTE-Advanced (LTE-A) cellular network causes severe interference to traditional cellular users and D2D pairs. To maintain the quality of service (QoS) of the cellular users and D2D pairs and reduce the interference, we propose a distance-based resource allocation and power control scheme using fractional frequency reuse (FFR) technique. We calculate the system outage probability, total throughput and spectrum efficiency for both cellular users and D2D pairs in terms of their signal-to-interference-plus-noise ratio (SINR). Our simulation results show that the proposed scheme reduces interference significantly and improves system performance compared to the random resource allocation (RRA) and resource allocation (RA) without sectorization scheme.

The present paper focuses on the application of the base station cooperation (BSC) technique in fractional frequency reuse (FFR) networks. Fractional frequency reuse is considered to be a promising scheme for avoiding the inter-cell interference problem in OFDMA cellular systems, such as WiMAX, in which the edge mobile stations (MSs) of adjacent cells use different subchannels for separate transmission. However, the problem of FFR is that the cell edge spectral efficiency (SE) is much lower than that of the cell center. The BSC technique, in which adjacent BSs perform cooperative transmission for one cell edge MS with the same channel, may improve the cell edge SE. However, since more BSs transmit signals for one cell edge MS, the use of BSC can also increase the inter-cell interference, which might degrade the network performance. In this paper, with a focus on this tradeoff, we propose an adaptive BSC scheme in which BSC is only performed for the cell edge MSs that can achieve a significant capacity increase with only a slight increase in inter-cell interference. Moreover, a channel reallocation scheme is proposed in order to further improve the performance of the adaptive BSC scheme. The simulation results reveal that, compared to the conventional FFR scheme, the proposed schemes are effective for improving the performance of FFR networks.

184-There is a huge demand for data traffic caused by increased usage of data-hungry applications on smart mobile devices. This has resulted into cellular network expansion and upgrade that have increased energy costs and generated environmental concerns. Distributed antenna systems (DAS) are applied to enhance the coverage of the cell via geographically distributed antennas elements (DAEs) which are connected to the base station that is located at the centre of the cell. In this paper, DAS is proposed as a network solution to fulfill increasing capacity demands while addressing the energy efficiency (EE) and environmental concerns associated with cellular network operation. Maximum Ratio Transmission (MRT) and Fractional Frequency Reuse (FFR) are applied to calculate the downlink ergodic spectral efficiency (SE), EE and energy consumption ratio (ECR). Nakagami-m fading and log-normal shadowing are considered. Our results demonstrate that DAS using MRT and FFR increases the spectral and energy efficiency of the network compared to a basic cellular network system.

International audience; With the increasing demand of mobile data traffic, cellular networks are evolving towards heterogeneous systems involving cells of different sizes (e.g., pico, micro, and macro cells). The presence of small cells is causing new interference issues that require the introduction of frequency reuse techniques suitable to manage both co-tier and cross-tier interference. In this paper, we propose a novel Soft Frequency Reuse (SFR) scheme for LTE-A, based on three frequency segments (named Three-Band Improved SFR, 3B-ISFR) where the Frequency Reuse Pattern (FRP) allocation scheme for micro cells is centralized at the level of each macro cell. This scheme is based on the exchange of measurements made by the micro cells with their macro cell (cognitive-assisted approach) and includes an intra-cell offloading algorithm to balance the load between cell-center and cell-edge of each micro/macro cell. The goodness of 3B-ISFR has been proved by means of performance comparisons with other schemes in the literature in terms of outage probability and average cell capacity

—Nowadays, there is a significant interest towardsevolved cellular systems to support the steady increase in capacityneeds. This paper deals with 4G Long Term Evolution (LTE),comparing two reuse schemes that belong to the family ofFractional Frequency Reuse (FFR), where the cell is divided intotwo parts (i.e., a central part and an edge one) adopting differentreuse patterns and different transmission powers. Our aim is toidentify the FFR scheme achieving higher capacity under somefairness constraints. Therefore, we perform an exhaustive-searchoptimization of the selected FFR scheme to maximize cell capacityin different conditions by means of Ns-3 simulations.Keywords—Long Term Evolution, Fractional Frequency Reuse I. I NTRODUCTION Long Term Evolution (LTE) is popularly known as a 4Gtechnology and can be considered as the technology of choicefor current and future cellular systems deployments [1]. LTEis an IP-based cellular technology, where the radio accessnetwork, called E-UTRAN (Evolved UMTS Terrestrial RadioAccess Network), consists of eNode Bs (eNBs) that interfacewith User Equipment terminals (UEs). Control and user planesdata are processed by the Packet Data Convergence Protocol(PDCP), the Radio Link Control (RLC) protocol, and theMedium Access Control (MAC) protocol, before being passedto the physical layer (PHY) for transmissions. IP packetsegmentation is performed at the RLC layer. The aim of thispaper is to compare different frequency reuse schemes ofthe Fractional Frequency Reuse (FFR) type for LTE and tooptimize cell capacity depending on different parameters.In this paper, we have adopted an improved capacityderivation approach with respect to our previous paper [2],considering that the sub-channels of central users are alwaysreserved for allocation to these users, thus achieving a higherutilization. Other papers address the issue to study the capacityof FFR schemes. Our study is original with respect to [3],since this work does not consider the constraint of a totalcell transmission power when differentiating the transmissionpower between sub-channels used in the cell center and inthe cell edge; this causes not to have outage conditions in thecentral area so that its radius is enlarged.II. LTE R

Best paper award of the 6th Joint IFIP Wireless and Mobile Networking Conference (WMNC'2013) Effective intercell interference (ICI) mitigation has been identified as a key challenge for emerging OFDMA cellular technologies such as Long Term Evolution (LTE). In order to address this issue, mobile operators have adopted static Intercell Interference Coordination (ICIC) strategies, including Fractional Frequency Reuse (FFR), given their low complexity and easy implementation. However, recent results made evident the need for additional research efforts as the performance of FFR is poor in realistic cellular deployments. Thus, this paper presents a solution to this problem by means of a novel multiobjective optimization framework able to adapt FFR to any realistic cellular layout. By tuning the operational parameters of FFR at cell level, the proposed scheme succeeds in finding solutions outperforming reference schemes and baseline designs in terms of network capacity and cell edge performance while keeping energy consumption as low as possible. Peer Reviewed Award-winning

Interference management techniques are critical to the performance of heterogeneous cellular networks, which will have dense and overlapping coverage areas, and experience high levels of interference. Fractional frequency reuse (FFR) is an attractive interference management technique due to its low complexity and overhead, and significant coverage improvement for low-percentile (cell-edge) users. Instead of relying on system simulations based on deterministic access point locations, this paper instead proposes an analytical model for evaluating Strict FFR and Soft Frequency Reuse (SFR) deployments based on the spatial Poisson point process. Our results both capture the non-uniformity of heterogeneous deployments and produce tractable expressions which can be used for system design with Strict FFR and SFR. We observe that the use of Strict FFR bands reserved for the users of each tier with the lowest average SINR provides the highest gains in terms of coverage and rate, while the use of SFR allows for more efficient use of shared spectrum between the tiers, while still mitigating much of the interference. Additionally, in the context of multi-tier networks with closed access in some tiers, the proposed framework shows the impact of cross-tier interference on closed access FFR, and informs the selection of key FFR parameters in open access., 23 pages, 6 figures, submitted: Transactions on Wireless Communications, July 20, 2011

We address the problem of analyzing the performances of interference-limited cellular networks in large-scale shadowing environments. Focusing on the fractional frequency reuse (FFR) framework, we examine how to optimally assign mobile users in a cell either to the full frequency reuse part or to the orthogonal part of the FFR band. Instead of using traditional Monte Carlo simulations, which do not provide sufficiently accurate results under important shadowing, we propose a fast and accurate numerical method. We consider a fast-fading environment and we use the ergodic capacity as the performance measure. Applying a distributed power control and scheduling strategy, we examine both cases where access points have knowledge of partial- or full-channel state information (CSI); for the latter, we also propose an approximated waterfilling strategy. The interest of our method lies in the fact that it allows for a fast and accurate analysis of the performances of FFR. In addition, it takes into account a broad range of shadowing environments.