Frequency Reuse Technique Research Articles

Throughput and Power Efficiency Analysis Considering Traffic Loads in FFR with Movable Boundary

ABSTRACTIn Fractional frequency reuse (FFR) technique, the available physical resource blocks are reused among different cells in a manner that co-channel interference and/or inter-cell interference effect is reduced. However, when the resources are highly utilized, the sharing of these resources becomes exhausted and/or limited, and this leads to a high interference and hence high call blocking probability. Therefore, this paper proposes a call admission control in FFR to improve the performance of the FFR-based cellular system. The results of the two quality of service (QoS) constraints, the call blocking probabilities and the resource utilizations for users are used for some design criteria of the cell inner/outer area to maximize the throughput and hence for the evaluation of the system power efficiency.

A novel frequency reuse technique for in‐building small cells in dense heterogeneous networks

In this paper, we address the important issue of reusing frequency resource in femtocells deployed in dense multi‐floor buildings over a large urban macrocell coverage to enhance network capacity and spectral efficiency using almost blank subframe (ABS)‐based enhanced inter‐cell interference coordination (eICIC) technique. Femtocell clustering and modeling an optimum number of ABS (OPNA) are, however, two major challenges to reuse frequency in femtocells deployed in buildings using ABS‐based eICIC. In this paper, we address these challenges by exploiting the high external wall penetration loss of any buildings and in‐between distance of neighboring buildings, and propose a femtocell clustering approach by considering all femtocells in any buildings as a femtocell cluster to avoid an additional computational complexity from clustering. We develop a frequency reuse and scheduling algorithm (FRSA) for an arbitrary number of ABSs for a multi‐tier network, which consists of in‐building femtocells and outdoor picocells in the coverage of an urban macrocell. We then propose a model for estimating the OPNA and derive an OPNA per femtocell cluster basis under two schemes, namely adaptive OPNA and non‐adaptive OPNA, in order to vary the number of ABSs imposed on femtocells within a building dynamically based on the presence of indoor macrocell users within the building to avoid cross‐tier interference with femtocells. An optimization algorithm for OPNA schemes is developed, and its implementation aspects are discussed. The impact of varying the number of ABSs and femtocells per building on the throughput performance of FRSA is analyzed through an extensive system‐level simulation, and the capacity outperformance of the adaptive over the non‐adaptive OPNA scheme is shown. Finally, a schematic of the scheduler implementation for FRSA is developed, and the capacity outperformance of FRSA over a number of existing works is shown. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Deployment of Resource Allocation and Power Control Schemes in Long Term Evolution Advanced (LTE-A) Hybrid Network

Long Term Evolution Advanced (LTE-A) Hybrid network integrates Femtocell and Macrocell networks to obtain better coverage and improved capacity. One of the limiting factors faced by Hybrid network is Inter-Cell Interference (ICI). One way to get rid of the ICI is through Inter-Cell Interference coordination technique. In the last few years, interference coordination such as Fractional Frequency Reuse (FFR) technique is considered as the utmost important research topic in LTE cellular technology. This paper revisited FFR method and deployed Dynamic Femtocell Resource Allocation (DFRA) scheme to ensure the resources assigned to Femtocells are mutually exclusive with adjacent Macrousers or adjacent Femtocells. Furthermore, in the scenario of high density Femtocells (when orthogonal resource exhausted), the power control schemes such as Power based Femtocell Base Station Power Control (PPC), SINR based Femtocell Base Station Power Control (SPC) and SINR based Neighboring Femtocell Power Control (SNPC) are integrated into the system. The deployment of the schemes has augmented the performance of the network and shows increment of 11.43% supported active users with an average data rate inclined by 22.19 Mbps.

Optimizing WiMAX: Mitigating Co-Channel Interference for Maximum Spectral Efficiency

The efficient use of radio spectrum is one of the most important issues in wireless networks because spectrum is generally limited and wireless environment is constrained to channel interference. To cope up and for increased usefulness of radio spectrum wireless networks use frequency reuse technique. The frequency reuse technique allows the use of same frequency band in different cells of same network considering inter-cell distance and resulting interference level. WiMAX (Worldwide Interoperability for Microwave Access) PHY profile is designed to use FRF (Frequency Reuse Factor) of one. When FRF of one is used it results in an improved spectral efficacy but also results in CCI (Co-Channel interference) at cell boundaries. The effect of interference is always required to be measured so that some averaging/ minimization techniques may be incorporated to keep the interference level up to some acceptable threshold in wireless environment. In this paper, we have analyzed, that how effectively CCI impact can be mitigated by using different subcarrier permutation types presented in IEEE 802.16 standard. A simulation based analysis is presented wherein impact of using same and different permutation base in adjacent cells in a WiMAX network on CCI, under varying load conditions is analyzed. We have further studied the effect of permutation base in environment where frequency reuse technique is used in conjunction with cell sectoring for better utilization of radio spectrum.

General expressions for downlink signal to interference and noise ratio in homogeneous and heterogeneous LTE-Advanced networks

The interference is the most important problem in LTE or LTE-Advanced networks. In this paper, the interference was investigated in terms of the downlink signal to interference and noise ratio (SINR). In order to compare the different frequency reuse methods that were developed to enhance the SINR, it would be helpful to have a generalized expression to study the performance of the different methods. Therefore, this paper introduces general expressions for the SINR in homogeneous and in heterogeneous networks. In homogeneous networks, the expression was applied for the most common types of frequency reuse techniques: soft frequency reuse (SFR) and fractional frequency reuse (FFR). The expression was examined by comparing it with previously developed ones in the literature and the comparison showed that the expression is valid for any type of frequency reuse scheme and any network topology. Furthermore, the expression was extended to include the heterogeneous network; the expression includes the problem of co-tier and cross-tier interference in heterogeneous networks (HetNet) and it was examined by the same method of the homogeneous one.

Low-overhead distributed resource allocation in relay-assisted multi-cell OFDMA systems

In this paper, we design a resource allocation (RA) scheme for the downlink of relay-assisted orthogonal frequency division multiple access (OFDMA) cellular networks. Our design goal is to achieve a high spectral efficiency with low signaling and computational complexity. To alleviate the complexity, the proposed scheme allocates the resources in a distributed manner, where each relay station (RS) or base station (BS) individually performs a joint subchannel and power allocation for its subordinate users. To increase the spectral efficiency, the subchannel reuse among RSs is allowed. The intra-cell/inter-cell interference between RSs due to the subchannel reuse is mitigated by applying a fractional frequency reuse technique. The proposed scheme is composed of the resource allocation at RS (RS-RA) and the resource allocation at BS (BS-RA). The RS-RA is formulated as an optimization problem of which the objective is to minimize the number of allocated subchannels while guaranteeing minimum rate requirements of subordinate users. The optimization objective of BS-RA is to maximize the total throughput of direct users. Simulation results show that the proposed scheme can achieve a high spectral efficiency with low signaling overhead.

Impact of Sub-Band Correlation on SFR and Comparison of FFR and SFR

In soft frequency reuse (SFR) when the user is classified as a cell-center user based on signal-to-interference-plus-noise-ratio in a sub-band, the user retains its sub-band. On the other hand, if the user is classified as a cell-edge user, a new sub-band is allocated. We analyze the impact of correlation between the cell-center sub-band and the cell-edge sub-band for a user when the SFR technique is used in a cellular orthogonal frequency division multiple access (OFDMA) system. The coverage probability (CP) and the average rate are derived for the following two cases: 1) when the sub-bands are independent and 2) when the sub-bands are completely correlated. We show that correlation significantly decreases the edge CP and the average rate of the SFR technique, and as the power control factor increases, the impact of correlation decreases. Fractional frequency reuse (FFR) and SFR techniques are compared and it is shown that the impact of correlation on the FFR is significantly lower. Furthermore, it is also shown that the FFR provides better edge CP and average rate when compared with the SFR in single-input single-output (SISO) networks, thereby suggesting that the FFR should be preferred over SFR in cellular SISO OFDMA systems. However, for single-input multiple-output networks, the SFR provides a better average rate when compared with the FFR, especially when the sub-band correlation is not significant. Finally, the impact of log-normal shadowing has been carefully studied.

Dynamic Fractional Frequency Reuse based on an Improved Water-Filling for Network MIMO

In Long Term Evolution-Advanced (LTE-A) systems, Inter-cell Interference (ICI) is a prominent limiting factor that affects the performance of the systems, especially at the cell edges. Based on the literature, Fractional Frequency Reuse (FFR) methods are known as efficient interference management techniques. In this report, the proposed Dynamic Fractional Frequency Reuse (DFFR) technique improved the capacity and cell edge coverage performance by 70% compared to the Fractional Frequency Reuse (FFR) technique. In this study, an improved power allocation method was adopted into the DFFR technique to reach the goal of not only reducing the ICI mitigation at the cell edges, but also improving the overall capacity of the LTE-A systems. Hence, an improved water-filling algorithm was proposed, and its performance was compared with that of other methods that were considered. Through the simulation results and comparisons with other frequency reuse techniques, it was shown that the proposed method significantly improved the performance of the cell edge throughput by 42%, the capacity by 75%, and the coverage by 80%. Based on the analysis and numerical expressions, it was concluded that the proposed DFFR method provides significant performance improvements, especially for cell edge users.

Resource Allocation for D2D Links in the FFR and SFR Aided Cellular Downlink

Device-to-device (D2D) communication underlying cellular networks, allows direct transmission between two devices in each other’s proximity that reuse the cellular resource blocks in an effort to increase the network capacity and spectrum efficiency. However, this imposes severe interference that degrades the system’s performance. This problem may be circumvented by incorporating fractional frequency reuse (FFR) or soft frequency reuse (SFR) in OFDMA cellular networks. By carefully considering the downlink resource reuse of the D2D links, we propose beneficial frequency allocation schemes, when the macrocell has employed FFR or SFR as its frequency reuse technique. The performance of these schemes is quantified using both the analytical and simulation results for characterizing both the coverage probability and the capacity of D2D links under the proposed schemes that are benchmarked against the radical unity frequency reuse scheme. The impact of the D2D links on the coverage probability of macrocellular users (CUs) is also quantified, revealing that the CUs performance is only modestly affected under the proposed frequency allocation schemes. Finally, we provide insights concerning the power control design in order to strike a beneficial tradeoff between the energy consumption and the performance of D2D links.

Overview of LTE Spectrum Sharing Technologies

Long-Term Evolution (LTE) communication systems feature advanced frequency reuse and interference coordination techniques providing faster and more secured mobile services. However, the network capacity in licensed spectrum is still behind market demands. Dynamic spectrum access or spectrum sharing in other frequently vacant or unlicensed frequency bands is considered an effective means to boost system throughput. Different from operations in licensed spectrum with exclusive access, LTE deployment needs to take into account the distinct regulations on channel access to each shared frequency band, in order to avoid interference to incumbent users, and to maintain fair play with peer operators in heterogeneous networks. This paper presents an overview on LTE spectrum sharing technologies on three popular spectrums, including the TV white-space channels, the frequently unused service-dedicated 3.5-GHz citizens broadband radio service spectrums, and the 5-GHz unlicensed bands. Existing spectrum usage in these frequency bands is analyzed, and the proposed methodologies on compliant operations are discussed for the reference of potential solutions to more efficient spectrum sharing mechanisms in the next generation mobile networks.

Fractional Frequency Reuse in DCO-OFDM-Based Optical Attocell Networks

In this paper a fractional frequency reuse (FFR) technique is considered in a direct-current optical orthogonal frequency-division multiplexing-based optical attocell network. An optical attocell network is proposed as a special type of visible light communication system that has the complete function of a cellular network. The cellular network is composed of many cells of extremely small size—the optical attocells. Two FFR schemes, strict fractional frequency reuse and soft frequency reuse, are considered. The signal-to-interference-plus-noise ratio (SINR) statistics and the spectral efficiency of the optical cellular system with FFR are analyzed. The performance of the systems with full frequency reuse and FFR is evaluated and compared. The results show that the FFR scheme can effectively achieve interference mitigation in an optical attocell network. The cell edge user SINR and spectral efficiency are significantly improved. Additionally, FFR provides improvements in average spectral efficiency. The effects of important parameters such as cell radius are also studied.

Handling interference in self-organizing femtocell networks through frequency-polarization diversity

The next generation heterogeneous networks are expected to offer higher data-rate and better QoS to the customers by leveraging smaller cells like femtocells and making use of orthogonal frequency division multiple access. However, uncoordinated dense deployment of femtocells in macrocell network pose unique challenges involving cross-tier interference and resource management which results in significant degradation of the system performance. As part of addressing these challenges for the successful integration of both technologies, this paper proposes the deployment of a self-organizing femtocell network that employs an opportunistic smart frequency reuse technique ---cross polarized complementary frequency allocation (CPCFA). It exploits the frequency and polarization diversity to mitigate interference in two-tier femto-macro networks. In this work, a strategy combining the adoption of reverse frequency allocation and orthogonal polarized transmission is analyzed as a potential solution for maximizing spectral efficiency and minimizing interference in the existing heterogeneous networks. Focus of the current work is on downlink transmission where the traffic is high and the deployment of femtocell is more beneficial. The results of analytic and simulation studies prove that CPCFA increases the scope for an easily implementable, remarkable opportunity in the context of two-tier femto-macro network that can substantially increase the system capacity as well as cell coverage without additional network complexities.

New Dynamic Resource Utilization Technique Based on Fractional Frequency Reuse

Worldwide interoperability for microwave access (WiMAX) base stations (BS) use the fractional frequency reuse (FFR) technique to control inter-cell interference in cellular networks. One of the challenges in FFR is the unused radio resource in the downlink (DL) sub-frame. This paper proposes a dynamic resource utilization approach to eliminate the resource wastage typical of the conventional FFR technique. The proposed approach not only enhances the radio resource utilization of the BS efficiently, but also takes into account the variations in the population density. We deal with the partial usage of sub-channel mode in the DL sub-frame of the WiMAX BS based on orthogonal frequency division multiplexing access. A new FFR data rate formula is derived based on theoretical analysis. Quantitative measurements demonstrate that the dynamic model gives optimal results, enhancing the conventional FFR in terms of a variety of metrics. The data rate, subcarrier efficiency, and spectral efficiency are increased by 2.176 Mbps, 0.14 bit/subcarrier/burst, and 0.218 bps/Hz, respectively. In addition, in the new approach, the DL sub-frame is fully utilized (100 %), the number of served users is increased by 28.57 %, and the number of utilized slots is increased by 34.48 %. The effective utilization of resources and bandwidth characteristic of this approach makes it a strong candidate for BS deployment in cellular networks where the user density changes constantly.

A Model Based on Poisson Point Process for Analyzing MIMO Heterogeneous Networks Utilizing Fractional Frequency Reuse

In this paper, we propose a tractable and flexible model for K-tier multiple-input-multiple-output (MIMO) heterogeneous networks (HetNets), with the fractional frequency reuse (FFR) technique, based on the spatial Poisson point process (PPP). The MIMO HetNets consist of K tiers of base stations (BSs), where each tier may differ in terms of the transmit power, the BSs' deployment density, the target signal-to-interference ratio, the number of antennas, and the MIMO technique. Since HetNets experience serious cross-tier interference, FFR, as an interference management technique, is found as a suitable solution. Due to the randomness of the BSs' locations, the PPP is more and more used to model them in HetNets. In this paper, we use different independent PPPs to model the BSs' locations of each tier, and we take different MIMO techniques into consideration. We focus on two main types of FFR techniques, i.e., strict FFR and soft frequency reuse, and we derive the coverage probability expressions of cell-edge users (the users at the cell edge). We also derive the average rate expressions and show the impact of the main parameters on the coverage probability under closed-access and open-access cases.

A Unified Framework for the Analysis of Fractional Frequency Reuse Techniques

Fractional frequency reuse (FFR) and soft frequency reuse (SFR) systems are an efficient cellular interference management technique to reduce inter-cell interference in multi-cell OFDMA networks. In this paper, a new and unified analytical framework for performance evaluation for both systems over a composite fading environment is presented. Explicit expressions are obtained for the area spectral efficiency (ASE) with both FFR and SFR, under fully loaded and partially loaded systems for downlink and uplink, and in generalized frequency reuse factor. The presented numerical result provides useful system design guidelines between the two systems. It is demonstrated that SFR outperforms FFR in a partially loaded scenario while the opposite is true for fully loaded system. The mathematical model is then extended to include the analysis of elastic data traffic in FFR system.

Uplink Soft Frequency Reuse for Self-Coexistence of Cognitive Radio Networks

The depletion of usable radio frequency spectrum has stimulated increasing interest in dynamic spectrum access technologies, such as cognitive radio (CR). In a scenario where multiple co-located CR networks operate in the same swath of white-space (or unlicensed) spectrum with little or no direct coordination, co-channel self-coexistence is a challenging problem. In this paper, we focus on the problem of spectrum sharing among coexisting CR networks that employ orthogonal frequency division multiple access (OFDMA) in their uplink and do not rely on inter-network coordination. An uplink soft frequency reuse (USFR) technique is proposed to enable globally power-efficient and locally fair spectrum sharing. We frame the self-coexistence problem as a non-cooperative game. In each network cell, uplink resource allocation (URA) problem is decoupled into two subproblems: subchannel allocation (SCA) and transmit power control (TPC). We provide a unique optimal solution to the TPC subproblem, while presenting a low-complexity heuristic for the SCA subproblem. After integrating the SCA and TPC games as the URA game, we design a heuristic algorithm that achieves the Nash equilibrium in a distributed manner. In both multi-operator and single-operator coexistence scenarios, our simulation results show that USFR significantly improves self-coexistence in spectrum utilization, power consumption, and intra-cell fairness.

A Simulation Framework for the Evaluation of Frequency Reuse in LTE-A Systems

Long Term Evolution Advanced (LTE-A) technology is considered as the most possible candidate for next generation mobile communications. LTE-A networks offer high capacity and are specified and designed to accommodate small, high performance, power-efficient end-user devices. Similarly to its predecessor LTE, LTE-A incorporates inter-cell interference mitigation methods in order to mitigate interference and to enhance efficiency in bandwidth usage. These methods include power and frequency allocation schemes that allow neighbouring cells and femtocells in heterogeneous networks to co-ordinately share and reuse available spectral resources, in order to avoid performance degradation for interference suffering cell-edge users. In this paper, the authors study the LTE-A multi-cell systems' performance using a simulation framework, which integrates several frequency reuse techniques and provides a user-friendly graphical presentation of the evaluation results. The optimal Fractional Frequency Reuse (FFR) configuration for the user-defined network instance is also determined, based on overall performance and fairness index metrics. Finally, the authors examine FFR techniques in two-tier femtocell/macrocell environments and evaluate them based on the optimization of different metrics, depending on the network operator's needs.

Frequency Reuse Techniques with a Distributed Antenna System

The performance of cellular networks is strongly limited by inter-cell interference. In order to reduce this interference, several techniques have been proposed, e.g., the frequency reuse techniques and distributed antenna system (DAS). This paper investigates the combinations of hard frequency reuse (HFR) and soft frequency reuse (SFR) techniques with DAS in a unique cell architecture, which are called DAS---HFR and DAS---SFR, respectively. This paper analytically quantifies the performance of the downlink multi-cell for DAS---HFR and DAS---SFR in terms of the average spectral efficiency. This also shows, the most appropriate frequency reuse technique depends not only on the average achievable data rate inside the cell, but also on the guaranteed achievable data rate (the minimum achievable data rate which is necessary to be obtained regardless of geographic location). The results show that DAS---SFR improves the achievable data rate of cell edges in a multi-cell environment as compared to a DAS---HFR when frequency reuse factor 1 is utilized. The results also show that DAS---SFR significantly increases the system capacity as compared to the DAS---HFR when frequency reuse factor 3 is utilized.

Performance Enhancement of LTE through Interference Reduction Techniques

Long Term Evolution (LTE) is the standard for wireless communication of high speed data and mobile terminal. Among the current emerging technologies like LTE based on orthogonal frequency division multiple access (OFDMA) technique, it found to be more attractive for high speed wireless communication. However co-channel interference (CCI) from the neighbouring cells is one of the limiting factors that degrade the LTE system. Fractional frequency reuse (FFR) technique is proposed to overcome the same as it is suitable for idealized cellular layout since power is not considered in this scheme. In this paper FFR is generalized and sub band allocation among user is made in optimal manner which increases the performance of the system.

Vertical Beamforming Inuence on Cellular Networks


 This paper proposes a vertical beamforming concept to a cellular network employing fractional frequency reuse technique. The reference antenna utilized in this paper is the one currently employed at base station. The idea of using two different vertical beams is proposed for cell-center and cell-edge regions, separately. The proposed concept is validated through computer simulation in terms of SINR and channel capacity. The obtained results indicate that the proposed concept can improve the performance of the cellular networks comparing with the ones employing horizontal beamforming and one spot beam covering cell sector.