Frequency Reuse Scheme Research Articles

Fractional Frequency Reuse Scheme for Device to Device Communication Underlaying Cellular on Wireless Multimedia Sensor Networks.

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.

Region splitting-based resource partitioning to enhance throughput in long term evolution - Advanced networks

In Long Term Evolution-Advanced networks, efficient resource partitioning is needed for improving throughput for User Equipment (UE). In this research, a region splitting-based resource partitioning scheme is proposed for enhancing the throughput of indoorMacro UE (MUE). The macrocell is divided into three regions, namely, the inner, centre and outer regions. The femtocells present in each region share the resources of the corresponding macrocell. The spectrum is partitioned into four non-overlapping sub-bands. These sub-bands are assigned to a cluster of three cells for mitigating cross-tier interference. The throughput of indoorMUE which is located at the boundary of inner region is analysed with respect to various numbers of femtocells and, MUE devices, angles made by MUE devices and femtocell transmission power. The proposed scheme has been compared with a fractional frequency reuse scheme in terms of inner-region radius. The inference drawn is that a maximum throughput enhancement of 29.7% has been achieved.

Interference Avoidance Using Dynamic Frequency Reuse For LTE-A System

To meet the increasing demand for spectrum in communication system, Long Term Evolution (LTE) system has been proposed. It allowed users to use a new and much wider spectrum comparing to the other previous technologies. To utilize the full capacity of the LTE system Frequency Reuse (FR) has been adapted. It is a promising aspect of transmission of high rate data stream with better system capacity and fading immunity in the modern Long-Term Evolution-Advanced (LTE-A) system. Fractional Frequency Reuse (FFR) is the commonly used frequency reuse technique to increase the system capacity. But the problem is, with introduction of FR, it also increases the Inter Cell Interference (ICI) of the system. The out of cell interference coming from the neighbouring e-NodeBs (eNB) as a result of using the same frequency band and they act as an interference source. This ICI decreases the system capacity, resulting in hampering of communication, browsing and in worst case no connection at all. This condition highly affects the users under a cell specially those who are located in the cell edge areas. To take care of this issue an approach called Dynamic Frequency Reuse scheme has been proposed in this paper to mitigate the interference thus increasing the system capacity. This scheme uses continuous assessment of resource allocation and choosing the best sub-band for the user with least interference. There is a sequential order to be maintained for the users with using off minimum Base Station (BS) transmit power. The cell edge area users are the primary concern in terms of increasing their service quality. MATLAB simulation software has been used to justify the theory that the proposed scheme is capable increase the capacity of the cell edge areas as well as the cell centre area user. The results achieved from the simulation also indicates that the proposed model can enhance the system capacity comparing to the existing FFR scheme.

Resource Allocation Scheme for Interference and Throughput Performance Improvement in LTE Femtocell Networks

Femtocells are one of the key enabling technologies for indoorcoverage extension and system capacity enhancement in LongTerm Evolution (LTE) cellular system. Cross-tier interferencebetween femtocells and macrocells is a great challenge. Inthis paper, a resource allocation scheme is proposed tominimize the interference and enhance the LTE femtocellthroughput. The fraction frequency reuse (FFR) scheme isconsidered for LTE cellular system. The proposed scheme isbased on using small number of resource blocks (RBs) whichefficiently selected according to their signal to interferenceplus noise ratio (SINR). Simulation results demonstrate thatthe proposed scheme increases the femtocell throughputusing small number of allocated resource blocks (RBs) andincreases SINR of femtocells users. Also, the proposedscheme significantly outperforms the conventional randomallocation scheme in terms of the achieved throughput andSINR values when the number of allocated RBs is only 20% ofthe total number of the available RBs.

A Resource Allocation Scheme with Fractional Frequency Reuse in Multi-cell OFDMA Systems

In this paper, a resource allocation scheme is proposed for multi-cell OFDMA systems in downlink under the fractional frequency reuse environments. The objective considers balancing between the maximization of the system throughput and the satisfaction of the user’s data rate requirement. Due to the severe co-channel interference for cellular networks with full frequency reuse, a dynamic fractional frequency reuse scheme is adopted in the cellular network which divides all subcarriers in each cell into two groups: a super group and a regular group. The dynamic fractional frequency reuse scheme can guarantee the intra-cell orthogonality and reduce the inter-cell interference. Therefore, the procedure of the proposed resource allocation scheme includes two main parts: frequency partition and subcarrier allocation. First, each subcarrier is assigned to either the super group or the regular group based on designed functions in all cells. Second, we allocate subcarriers to users by utilizing the designed functions. The designed functions are developed based on the proportional fairness scheduling, the logarithm transformation, and the Lagrangian technique. The designed function is coupled with the instantaneous data rate, the average data rate, and the data rate requirement. Simulation results show that the proposed scheme provides a higher system throughput and improves the outage probability compared with existing schemes.

Spectrum Allocation for Enhanced Cross-Tier Interference Mitigation with Throughput Improvement for Femtocells in a Heterogeneous LTE Cellular Network

Femtocells are the solution to improve cellular system capacity in indoor coverage. In two-tier networks, co-channel interference is a serious problem. In this paper, an efficient spectrum allocation scheme is proposed to improve signal to interference plus noise ratio (SINR) and the throughput for femtocell users. The proposed spectrum allocation scheme is based on reducing the cross-tier interference by allocating the best group of the available resource blocks (RBs) that achieve minimum interference level for femtocell users. The soft frequency reuse scheme is considered for long term evolution cellular system due to its ability to decrease the inter-cell interference and enhances the throughput for macrocells. Simulation results show that the proposed spectrum allocation scheme efficiently increases the SINR for femtocell users and enhances both the femtocell throughput and the total cell throughput compared to the conventional random allocation scheme. In addition, it is shown that the best performance of proposed scheme in terms of highest SINR and highest throughput is achieved by allocating only one-third of the available RBs for femtocell.

Two-Color Scheme for a Multi-Beam Satellite Return Link: Impact of Interference Coordination

The return link of broadband satellite systems has recently received more attention due to the spread of multi-beam antennas which enable spatial frequency reuse, and thus increase drastically the number of users that can potentially be served by one satellite. While interference isolation has so far been the way to go, with regular four-color frequency reuse scheme, there is a growing interest in densifying the frequency usage as is being done in cellular networks. In this paper, we address the return link radio resource allocation challenges, from spectral resource allocation to user scheduling, including modulation and coding scheme (MODCOD) selection. Our contributions highlight the potential gains of a two-color scheme and shed light on several levers to reap its benefits through interference management. We first consider the possibility to use a two-color scheme, while keeping the MODCOD selection and the scheduling local to each beam and we show that even though it yields a potential performance gain (+16%) with respect to the state of the art (SoA) (based on four colors), it is not viable due to a very high-block loss rate. Therefore, we propose a simple—yet fast and efficient—coordinated MODCOD selection process that alleviates the need of estimating interference and reduces drastically decoding failures. This coordination step offers significant gains (+58%) over the SoA, while leaving the per beam scheduler unchanged. Finally, we formulate a joint user scheduling and MODCOD selection problem across all beams and propose an offline heuristic to solve it efficiently. We obtain a 83% gain with respect to the SoA, but with higher computational complexity. Still, it confirms the great potential of coordinated scheduling.

Frequency Reuse of Beam Allocation for Multiuser Massive MIMO Systems

Massive multiple-input-multiple-output (MIMO) has become a promising technique to provide high-data-rate communication in fifth-generation mobile systems, thanks to its ability to form narrow and high-gain beams. Among various massive MIMO beamforming techniques, the fixed-beam scheme has attracted considerable attention due to its simplicity. In this paper, we focus on a fixed-beam based multiuser massive MIMO system, where each user is served by a beam allocated to it. To maximize the sum data rate, a greedy beam allocation algorithm is proposed under the practical condition that the number of radio frequency chains is smaller than the number of users. Simulation results show that our proposed greedy algorithm achieves nearly optimal sum data rate. As only the sum data rate is optimized, there are some “worst-case” users, who could suffer from strong inter-beam interference and thus experience low data rate. To improve the individual data rates of the worst-case users while maintaining the sum data rate, an adaptive frequency reuse scheme is proposed. Simulation results corroborate that our proposed adaptive frequency reuse strategy can greatly improve the worst-case users’ data rates and the max-min fairness among served users without sacrificing the sum data rate.

Device-to-Device Communications in Multi-Cell LTE-Advanced Networks with Cloud Radio Access Network Architecture

Device-to-device communications underlaying LTE-Advanced wireless networks reuse cellular spectrum to establish direct links between users without traversing the base stations or the cellular network. In this paradigm, there is a need to allocate the resources with a view to maximizing the utility (e.g., the total throughput) and mitigating the interference caused by sharing the same spectrum between cellular users and D2D pairs. This article, which is tutorial in nature, proposes a scheme for maximizing the total number of active D2D pairs and reused channels while minimizing the aggregate transmit power of cellular users and D2D pairs and maintaining their required QoS to the extent possible. This reduces the load on base stations, lessens power consumption, and improves spectrum efficiency beyond the conventional cellular frequency reuse schemes. Unlike many existing works that assume a single cell, we consider a multi-cell scenario in which the transmitter and the receiver of each D2D pair can be in the same cell or in different cells, and each user can simultaneously transmit over multiple reused channels. The allocation is done via a centralized baseband processing in the cloud radio access network architecture. Simulations show that via our proposed scheme, more users (both cellular users and D2D pairs) can simultaneously communicate, and the total system throughput is also significantly increased.

Cross‐polarisation discrimination models assessment and improvement on earth‐space propagation paths at Ka and V‐bands

The performance of the satellite communication systems employing polarisation diversity or frequency-reuse schemes to improve the spectral efficiency is degraded due to the depolarisation-induced interference originated by raindrops and ice particles present along the Earth-Space propagation path. Two models account for both rain and ice contributions. One predicts the long-term cumulative distribution function (CDF) of cross-polarisation discrimination (XPD). The other predicts the relationship between XPD and co-polar attenuation (CPA) and it was derived considering exclusively data at the V-band. In this study, the former model is improved by considering the individual ice and rain contributions and their combined effects, while the latter is validated against new measurements at the Ka band. New models are then proposed for the XPD-CPA relationships at the Ka-band taking into account both rain and ice contributions and also their combined effects. Finally, the predictions provided by the first model are usually converted to the corresponding XPD-CPA relationship using the long-term first-order statistics of rain attenuation, (incorrectly) considering that the equiprobability hypothesis applies. A new approach for the conversion of the XPD CDF into the corresponding XPD-CPA relationship is presented.

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.

On the Design of OFDMA-Based FFR-Aided Irregular Cellular Networks With Shadowing

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.

Energy- and Spectral-Efficient Resource Allocation Algorithm for Heterogeneous Networks

In this paper, the tradeoff between energy efficiency and spectral efficiency in multicell heterogeneous networks is investigated. Our objective is to maximize both energy efficiency and spectral efficiency of the network, while satisfying the minimum rate requirements of the users. We define our objective function as the weighted summation of energy efficiency and spectral efficiency functions. The fractional frequency reuse (FFR) scheme is employed to suppress intercell interference. We formulate the problem as cell-center boundary selection for FFR, frequency assignment to users, and power allocation. The optimal solution of this problem requires exhaustive search over all cell-center radii, frequency assignments, and power levels. We propose a three-stage algorithm and apply it consecutively until convergence. First, we select the cell-center radius for the FFR method. Second, we assign the frequency resources to users to satisfy their rate requirements and also maximize the objective function. Third, we solve the power allocation subproblem by using the Levenberg-Marquardt method. Minimum rate requirements of users are also included in the solution by using dual decomposition techniques. Our numerical results show a Pareto-optimal solution for energy efficiency and spectral efficiency. We present energy efficiency, spectral efficiency, outage probability, and average transmit power results for different minimum rate constraints. Among other results, we show that, in a particular setting, 13% energy efficiency increase can be obtained in a multicell heterogeneous wireless network by sacrificing 7% spectral efficiency.

Performance Measurement Model of Mobile User Connectivity in Femtocell/Macrocell Networks using Fractional Frequency Re-use Scheme

Technologies are traversing to its new dimensions every day. As part of this progression, mobile cellular system is at the summit of its constant advancement. The usage of Femtocells in mobile cellular system has created a massive impact on its architecture. Likewise, the incorporation of femtocells in macrocells for 4G mobile network communication services (like-voice calls, data services, etc.) among mobile stations within few meters has been one of the promising approaches. There is a femto access point (FAP) in Femtocell which handles the authorization of the user around it. Among the three various access methods, FAP allows only the authorized users except the macro cell users in Closed Access Method (CAM). But for Open Access Method (OAM), any type of crossing macrocell user within the radio coverage of femtocell and the femtocell users can get FAP access. To reduce the cross-tier interferences OAM is more efficient, because it deals with both type of users within the femtocell coverage. This paper proposes a performance measurement model for mobile connection probability depending on the mobility factor of mobile users and the communication range in femtocell/ macrocell networks. Furthermore, a derivation has been done to get the optimum result from the outage and connectivity probability under different number of femtocells and mobile users. Finally, to maximum the spectral efficiency for the probable frequency allocation, a Fractional Frequency Re-use scheme among the networks has been proposed.

Multichannel analysis of soft frequency reuse and user association in two-tier heterogeneous cellular networks

The cell range expansion (CRE) is encouraged to be applied in the heterogeneous cellular networks (HCNs), to enhance the capacity by offloading macro users to small cells. However, the enhanced inter-cell interference coordination (eICIC) techniques are supposed to be used for mitigating the strong cross-tier interference suffered by the offloaded users and small cell edge users. To address this, a novel soft frequency reuse (SFR) scheme is adopted in this paper. We analyze multichannel downlink scenarios for the SFR scheme using the tools of stochastic geometry. In consideration of the random resource allocation and practical cell load model, the analytical results of coverage probability and average user rate are derived and validated through Monte Carlo methods. Furthermore, our results can reduce to simple closed-form under reasonable special case for modern urban cellular networks. The main evaluation of the performance in terms of average user rate is presented, and the optimal combination of association bias and parameters of the SFR scheme is also investigated. Numerical results show that the SFR scheme outperforms the frequency resource partitioning (FRP) scheme in any load condition. Moreover, the CRE with SFR scheme can improve the average user rate significantly.

Inter-cell Interference Management Technique for Multi-Cell LTE-A Network

In modern cellular system such as LTE Advanced (LTE-A), frequency reuse scheme is targeted to be applied to fulfill the requirement of high capacity broadband access and high spectrum efficiency. But this kind of frequency planning may lead to the worse inter-cell interference (ICI) level experienced especially by a user located at the cell edge. Soft Frequency Reuse (SFR) is considered as an effective way to mitigate inter-cell interference and maintain capacity. We propose a power division SFR, known as multi level SFR technique to minimize ICI in a designed LTE-A network for sub-urban environment. Service area of LTE-A network was first developed to deploy particular number of eNB by using LTE network planning tools in the frequency of 1800 MHz with the use of SISO (Single Input Single Output) antennas. Coverage dimensioning and propagation consideration determine LTE-A parameters which were used in the simulation. Monte carlo simulation is executed to examine the performance of SFR for LTE-A downlink transmission to address different power ratio and traffic loads problem. Both performance of cell edge users and overall cell performance are evaluated in terms of CINR, BLER, and throughput. Performance with SFR is also compared with the classical frequency reuse one and three.

MOCA: Multiobjective Cell Association for Device-to-Device Communications

It is widely accepted that device-to-device (D2D) communication is envisaged to become the key enabler of direct localized communication between mobile nodes in future wireless networks. However, little attention has been paid to an important aspect that can potentially affect both the performance of D2D and cellular transmissions, which is that of the D2D cell association. In this paper, a multiobjective cell association (MOCA) optimization framework for orchestrating a large number of D2D links in a multicell network is introduced. To this end, and without loss of generality, a differentiated Fractional Frequency Reuse (FFR) scheme is considered as the interference-limiting method, especially for cell-edge users, and we assume the provision of different resource pools for D2D and cellular users, which can vary according to their location. Under this assumption, we develop a set of integer linear programming optimization formulations for D2D links, part of which fall within the coverage area of different neighboring base stations. The main purpose is to achieve improved network traffic balancing via an efficient cell association scheme. Furthermore, we provide an iterative randomized resource allocation algorithm ( i-RRA ), which roots its logic on the differentiated FFR model in order to increase the overall network throughput. A wide set of numerical investigations demonstrate the benefits offered by MOCA, as well as the throughput gains that can be achieved through i-RRA , compared to existing solutions.

Soft frequency reuse-based optimization algorithm for energy efficiency of multi-cell networks

This paper studies the optimization problem of energy efficiency in multi-cell networks with multiple users such as 5G network. However, the spectrum allocation and inter-cell interference (ICI) in multi-cell networks are the important challenges. The Soft Frequency Reuse (SFR) scheme which manages the spectrum and reduces ICI is used to build SFR-cellular networks. We take the global energy efficiency of the SFR-cellular network as the objective function of the optimal problem to obtain the maximum energy efficiency. Unfortunately, the objective function is a non-concave function, which is significantly difficult to be solved directly. Therefore, we utilize the fractional program, successive convex approximation, Lagrange dual, and Karush–Kuhn–Tucker (KKT) conditions to transform the objective function into a concave function. In such case, we could solve the problem with the convex optimization method. Finally, based on SFR, we propose a global energy efficiency optimization algorithm to search for the optimal energy efficiency of networks. Simulation results show that the proposed algorithm holds the better performance.

A Dynamic Inter-cellular Bandwidth Fair Sharing scheduler for future wireless networks

Due the limitation of the frequency spectrum, channel assignment remains a main challenge in future wireless networks. In this context, the Inter-cellular Scheduling Scheme consists in dynamically allocating/reallocating the bandwidth to the cells, adapting it to the inhomogeneous traffic distribution that appears in a multi-cell environment. More precisely, it dynamically selects the cell that experiences the highest difficulties and grants it supplementary radio resources borrowed from its neighboring under-loaded donor ones. In this paper, we introduce and explain the concept of minimal bandwidth, which corresponds to the minimal amount of radio resources that an under-loaded cell must keep in order to be protected from sudden and uneven high bit rates peaks. This minimal bandwidth guarantees a minimal service. The majority of the existing works on dynamic channel assignment neglects the use of this important parameter or consider it as a static one. In this context, we introduce a novel multicellular scheduler called Dynamic Inter-cellular Bandwidth Fair Sharing that dynamically computes the minimal bandwidth of a cell according to its ratio of used bandwidth and available bandwidth. In the first step, the proposed solution is applied to the channel assignment scheme Reuse 3 and compared to a state of the art inter-cellular scheduling strategy in order to underline the benefits of the dynamic minimal bandwidth adaptation. In the second step, we have applied our methodology to the Fractional Frequency Reuse (FFR) scheme and compared it to the four frequency allocation schemes, Reuse 1, Reuse 3, FFR and Soft Frequency Reuse (SFR), as well as to a reference Dynamic FFR (D-FFR) solution that does not take into consideration the needs of the cells in terms of minimal bandwidth while redistributing the radio resources. Simulation results show that although the D-FFR scheme enhances the performances of the overloaded cell, it deteriorates the performance of the neighboring under-loaded ones. On the contrary, our solution called FFRDIBFS improves the provided Quality of Service (QoS) of both the congested cells and the whole cellular network.

Three-Stage Resource Allocation Algorithm for Energy-Efficient Heterogeneous Networks

In this paper, we investigate the energy efficiency of downlink transmissions in heterogeneous networks. Our objective is to satisfy the rate requirement of users while maximizing the energy efficiency of the network. We employ the fractional frequency reuse (FFR) scheme to increase the energy efficiency of downlink transmissions and to eliminate outages for the cell-edge users. We formulate the joint cell-center boundary selection for FFR, scheduling, and power allocation problems. This formulation gives us a mixed discrete (selection of the cell-center boundary selection for FFR and scheduling) and continuous (power allocation) optimization problem which is hard to solve jointly. In order to solve this problem, we propose a three-stage resource allocation algorithm. In the first stage, we propose a dynamic method to determine the cell-center region boundaries. In the second stage, we employ the Lagrangian-directed scheduler algorithm to incorporate the rate requirements of users. The third stage solves the power allocation subproblem using the Levenberg–Marquardt method combined with dual decomposition. In order to make the base stations further reduce intercell interference, interference pricing mechanism is applied. This scheme penalizes the utility of a base station with the interference it creates. The performance of the proposed algorithm is simulated in a long-term evolution (LTE) network simulation tool. Our numerical results reveal that significant gains in terms of energy efficiency can be achieved with the proposed algorithm. The outage probability is also significantly reduced.