Frequency Reuse Scheme Research Articles

Optimal Downlink and Uplink Fractional Frequency Reuse in Cellular Wireless Networks

Densely deployed cellular wireless networks, which employ small cell technology, are being widely implemented. Mitigating the impact of inter- and intracell signal interferences induced by the operations of these networks is a challenging yet essential task. In this paper, we consider adaptive rate scheduling for a transmitting node, regardless of whether it is a base station (BS) or a mobile user. We aim to maximize the system's throughput through the employment of fractional frequency reuse (FFR) schemes. Each BS employs either an omnidirectional or a directional antenna system. We derive the optimal configuration of the FFR scheme and evaluate the ensuing system's performance behavior under absolute and proportional fairness requirements. To maximize the attained throughput by mobiles, we determine the best method to use to classify cell users into interior and edge mobiles. The bandwidth levels allocated for serving interior and edge mobiles are optimized. We derive approximate closed-form mathematical expressions for calculating the probability distributions of the interference signal levels measured at the destined receivers. We account for the impact of the classification process on intercell interference power levels. Under an absolute fairness requirement, we show that optimally configured FFR schemes lead to much enhanced performance. We show that the optimally configured directional-FFR schemes increase the throughput capacity by a factor of about 60% relative to that obtained by using optimal omnidirectional-FFR schemes. The analyses and simulation results presented in this paper serve to characterize the performance behavior attainable by using such small cell deployed cellular wireless network systems when employing the underlying configurations.

Analysis of Bandwidth Requirement of Users in Flexible Reuse Cellular Networks

In flexible frequency reuse scheme namely fractional frequency reuse (FFR), the total frequency resource is divided logically into cell center and cell edge user bands. However, while frequency resource is partitioned into two segments, the amount of average bandwidth required by cell center and cell edge users is quite different and influences the system performance and design. We developed the analytical approach to evaluate the average bandwidth required by cell center and cell edge users for real time (RT) traffic. It is seen that the analytical results are closely matched with the simulations and indicate that the model is a good approximation for bandwidth requirement of users in a cellular environment.

Impact of Correlated Interferers on Coverage and Rate of FFR and SFR Schemes

The coverage probability (CP) and the average rate expressions when fractional frequency reuse (FFR) or soft frequency reuse (SFR) schemes are employed in single-input–multiple-output (SIMO) network are derived when the interferers undergo correlated Rayleigh fading. It is analytically shown that both the CP and the rate are higher in the presence of the correlated interferers (when the interferers are positively correlated) when compared with the case where the interferers are independent. It is also shown that the impact of correlation on SFR is more when compared with FFR, and it decreases with an increase in the power control factor. The authors show that the average rate achieved by FFR is higher when compared with the SFR in SISO networks for both the independent and correlated cases. However, the situation is reversed for SIMO networks. The impact of large-scale fading has also been briefly studied.

A dynamic distributed frequency reuse scheme for OFDMA downlink cellular networks

A dynamic distributed frequency reuse scheme for OFDMA downlink cellular networks

A Survey on High Efficiency Wireless Local Area Networks: Next Generation WiFi

The emerging paradigm of the Internet of Everything, along with the increasing demand of Internet services everywhere, results in a remarkable and continuous growth of the global Internet traffic. As a cost-effective Internet access solution, WiFi networks currently generate a major portion of the global Internet traffic. Furthermore, the number of WiFi public hotspots worldwide is expected to increase by more than sevenfold by 2018. To face this huge increase in the number of densely deployed WiFi networks, and the massive amount of data to be supported by these networks in indoor and outdoor environments, it is necessary to improve the current WiFi standard and define specifications for high efficiency wireless local area networks (HEWs). This paper presents potential techniques that can be applied for HEWs, in order to achieve the required performance in dense HEW deployment scenarios, as expected in the near future. The HEW solutions under consideration includes physical layer techniques, medium access control layer strategies, spatial frequency reuse schemes, and power saving mechanisms. To accurately assess a newly proposed HEW scheme, we discuss suitable evaluation methodologies, by defining simulation scenarios that represent future HEW usage models, performance metrics that reflect HEW user experience, traffic models for dominant HEW applications, and channel models for indoor and outdoor HEW deployments. Finally, we highlight open issues for future HEW research and development.

Survey of ICIC techniques in LTE networks under various mobile environment parameters

LTE networks' main challenge is to efficiently use the available spectrum, and to provide satisfying quality of service for mobile users. However, using the same bandwidth among adjacent cells leads to occurrence of Inter-cell Interference especially at the cell-edge. Basic interference mitigation approaches consider bandwidth partitioning techniques between adjacent cells, such as frequency reuse of factor m schemes, to minimize cell-edge interference. Although SINR values are improved, such techniques lead to significant reduction in the maximum achievable data rate. Several improvements have been proposed to enhance the performance of frequency reuse schemes, where restrictions are made on resource blocks usage, power allocation, or both. Nevertheless, bandwidth partitioning methods still affect the maximum achievable throughput. In this proposal, we intend to perform a comprehensive survey on Inter-Cell Interference Coordination (ICIC) techniques, and we study their performance while putting into consideration various design parameters. This study is implemented throughout intensive system level simulations under several parameters such as different network loads, radio conditions, and user distributions. Simulation results show the advantages and the limitations of each technique compared to frequency reuse-1 model. Thus, we are able to identify the most suitable ICIC technique for each network scenario.

Co-channel interference cancelation at the user terminal in multibeam satellite systems

Summary We study the applicability of soft interference cancelation in the forward link of multibeam satellite systems with focus on mobile terminals. We adopt a standard currently used in commercial satellite systems as a reference. The multibeam satellite antenna radiation diagram has been generated using a physical optics reflector model while a widely adopted channel model has been used for the land mobile satellite channel. The interference pattern has been derived using a system simulator developed by the European Space Agency. Starting from the analysis of the interference pattern, we study the application of a low-complexity soft interference cancelation scheme for commercial applications. Our results show that, under realistic conditions, a two-colors frequency reuse scheme can be employed while guaranteeing service availability across the coverage and keeping the complexity at the user terminals relatively low. Copyright © 2015 John Wiley & Sons, Ltd.

Co-channel interference suppression techniques for full duplex cellular system

Co-frequency and co-time full duplex (CCFD) is a promising technique for improving spectral efficiency in next generation wireless communication systems. However, for the applications of CCFD in a cellular network, severe co-channel interference is an essential problem. Specifically, there are two significant interferences, i.e., inter-terminal interference (ITI) and inter-cell interference (ICI), which lead to an obvious performance degradation. In this paper, two techniques are proposed for suppressing the ITI and ICI in a CCFD cellular system, respectively. The first technique is obtained by modeling the three-node CCFD system as the Z-channel. After deriving the sum-capacity of the Z-channel, a sum-capacity-achieving scheme based on successive interference cancellation (SIC) is proposed. The second technique is designed by combining the fractional frequency reuse scheme with CCFD. The performance gains of the proposed two techniques in terms of signal-to- interference plus noise ratio (SINR) and sum-capacity are analyzed. Simulation results show that the proposed scheme can achieve significant interference suppression performance and higher system capacity, especially for cell edge users.

Coverage Probability and Achievable Rate Analysis of FFR-Aided Multi-User OFDM-Based MIMO and SIMO Systems

Expressions are derived for the coverage probability and average rate of both multi-user multiple input multiple output (MU-MIMO) and single input multiple output (SIMO) systems in the context of a fractional frequency reuse (FFR) scheme. In particular, given a reuse region of $\frac{1}{3}$ (FR3) and a reuse region of 1 (FR1) as well as a signal-to-interference-plus-noise-ratio (SINR) threshold $S_{th}$ , which decides the user assignment to either the FR1 or FR3 regions, we theoretically show that: $1)$ the optimal choice of $S_{th}$ which maximizes the coverage probability is $S_{th} = T$ , where $T$ is the target SINR required for ensuring adequate coverage, and $2)$ the optimal choice of $S_{th}$ which maximizes the average rate is given by $S_{th}= T^{\prime}$ , where $T^{\prime}$ is a function of the path loss exponent, the number of antennas and of the fading parameters. The impact of frequency domain correlation amongst the OFDM sub-bands allocated to the FR1 and FR3 cell-regions is analysed and it is shown that the presence of correlation reduces both the coverage probability and the average throughput of the FFR network. Furthermore, the performance of our FFR-aided MU-MIMO and SIMO systems is compared. Our analysis shows that the (2 $\times$ 2) MU-MIMO system achieves 22.5% higher rate than the (1 $\times$ 3) SIMO system and for lower target SINRs, the coverage probability of a (2 $\times$ 2) MU-MIMO system is comparable to a (1 $\times$ 3) SIMO system. Hence the former one may be preferred over the latter. Our simulation results closely match the analytical results.

Multi-hop Cellular Networks for LoadBalancing and Interference CoordinationUsing OFDMA

Multi hop cellular networks (MCNs) use multiple low-power transmitters for high throughput and coverage of large area in a network. The network consists of Base stations (BSs) and Relay Stations (RSs) placed inside the center and edge of the network that could transmit the frequency simultaneously. The network performance can be affected by the mobile stations which lead to co channel interference (CCI) near the coverage boundary of the cell. The traffic quality and the quality of service (QOS) can hardly be guaranteed due to the unbalanced user distribution. The static method is used which divides the network into a tri-sector network according to the frequency reuse scheme that works with the downlink of OFDMA-based specification. The throughput increases by accommodating more users in the coverage area in a MCNs. Interference in the cell edge is avoided by implementing the avoidance algorithms where the base stations are placed in the centre of the cell and in tri-sector of the network.

Adaptive Resource Allocation for Interference Management in Small Cell Networks

We consider a femto cellular network consisting of multiple neighboring femtocells, e.g., in an enterprise deployment such as shopping malls, stadiums, or corporate premises. We present a practical but suboptimal channel assignment and interference management algorithm for fractional frequency reuse (FFR) wireless networks. More specifically, we propose an adaptive graph coloring approach for resource allocation with the goal of interference management among femtocells as well as achieving fairness among users. While the global-optimum solution has exponential complexity, our proposed scheme has a linear complexity in the number of femtocells. Although suboptimal, we have evaluated our algorithm in small scenarios, where direct evaluation is possible, and found that the achieved minimum user rate using the proposed algorithm is 85% of the optimal minimum rate. Additionally, we have analyzed several practical design considerations of our proposal such as channel feedback, latency, and computational complexity. We demonstrate the performance of our proposed solution against various alternatives and show that it provides better performance under various environment parameters. For example, in a dense femtocell deployment, the performance was improved by 47% over a full frequency reuse scheme.

Dynamic frequency reuse based on guard regions in two‐layer heterogeneous networks

The guard region for a randomly select user is introduced based on the stochastic geometry model. The guard region, through which a frequency reuse criterion is proposed, is calculated based on parameters such as user position, path loss exponents and transmission power. A dynamic frequency reuse scheme based on the guard regions of macrocell users is proposed to mitigate inter-layer interference. A frequency reuse criterion, which changes along with user position adaptively and is derived through stochastic geometry theory, is believed to be the first effort that can be found in the literature.

Alleviating Interference through Cognitive Radio for LTE-Advanced Network

In the LTE-Advanced network, some femtocells are deployed within a macroecell for improving throughput of indoor user equipments (UEs), which are referred to as femtocell UEs (FUEs). Cross-tier interference is an important issue in this deployment, which may significantly impact signal quality between Macrocell Base Stations (MBSs) and Macrocell User Equipments (MUEs), especially for MUEs near the femtocell. To relieve this problem, the Third Generation Partnership Project Long Term Evolution-Advanced (3GPP LTE-Advanced) de<br /> fined the cognitive radio enhanced femtocell to coordinate interference for LTE-Advanced Network. Cognitive radio femtocells have the ability to sense radio environment to obtain radio parameters. In this paper, we investigated the performance of existing schemes based on fractional frequency reuse. Therefore, we proposed a scheme with cognitive radio technology to improve the performance of fractional fre-quency reuse scheme. Simulation results showed that our scheme can effectively enhance average downlink throughput of FUEs as well as the total downlink throughput in LTE-Advanced Networks.

Corrections to and Comments on “Throughput and Optimal Threshold for FFR Schemes in OFDMA Cellular Networks” [Aug 12 2776-2785

In a recent paper published in these Transactions, Xu et al. (see ibid., vol. 11, no. 8, pp. 2776–2785, Aug. 2012) proposed an analytical framework to calculate the throughput and optimal threshold for fractional frequency reuse (FFR) schemes in orthogonal frequency division multiple access (OFDMA) cellular networks. This correspondence points out a problem in the original derivation of Xu et al. and how this affects the claimed performance of the maximum signal-to-interference-plus-noise ratio (MSINR) scheduling rule. A fix to this problem is presented in this work, which turns out to extend the applicability of the analysis beyond the case studied by Xu et al. and at the same time shows how the performance of the round robin (RR) scheduling rule can be obtained as a special case of the MSINR scheduler. Monte Carlo simulation results demonstrate the validity and merits of our proposed approach.

Resource allocation in integrated femto–macrocell networks based on location awareness

This study presents an efficient fractional frequency reuse scheme for macrocell network which uses six directional antennas to cover the outer region and analyses the performance. Cross-tier interference between macrocell and femtocell networks leading to throughput and outage probability degradation is a major issue in two-tier networks when femtocells are deployed in co-channel with macrocells. In this study, the received interference from the macrocell network to femtocell network is analysed. Then, based on the degree of received interference, an algorithm for orthogonal resource allocation to femtocells with low cross-tier interference is presented. According to the introduced scheme, macrocell uses all resource blocks along with a portion of the spectrum allocated to femtocell while both networks operate simultaneously. Closed-form expressions for downlink throughput and outage probability of femtocells are also attained as well as the throughput of macrocell network. The results demonstrate that the proposed hierarchical cellular network achieves higher throughput and lower outage probability for femtocell when compared to other hierarchical macro–femto cellular networks.

Performance analysis of flexible reuse in cellular networks

Flexible frequency reuse schemes namely fractional frequency reuse (FFR) and soft frequency reuse (SFR) are suggested in the literature to improve the cell edge throughput over unity frequency reuse in orthogonal frequency division multiple access networks. In this study, the authors focus on real time (RT) traffic for which blocking probability and Erlang load are the important performance metrics. Both FFR and SFR have signal-tointerference-plus noise-ratio (SINR) threshold and power ratio as important design parameters, whereas FFR has a bandwidth partitioning ratio as an additional parameter. They investigate the cell capacity and the cell edge performance in terms of Erlang load with blocking probability constraint brought about by the suitable choice of these parameters. They also analyze the fairness aspect which is a critical indicator of user satisfaction. They give a complete comparison between FFR and SFR for the cell edge as well as total cell for both RT and BE traffics. For RT traffic, with proper choice of the parameters, the cell edge and the total cell performance in FFR and SFR is improved by a notable gain over the reference scheme. For BE traffic, both schemes provide significant gains at cell edge over reuse one and reuse three schemes.

Adaptive Soft Frequency Reuse Scheme for Wireless Cellular Networks

Spectrum scarcity and intercell interference (ICI) are two fundamental limiting factors in wireless cellular systems. Soft frequency reuse (SFR) has been proposed as an effective way to manage the spectrum and reduce ICI in cellular systems. In a static SFR scheme, the allocations of transmit power or subcarriers in each cell are fixed prior to system deployment. This limits the potential performance of the SFR scheme. In this paper, we propose an intercell resource-allocation algorithm, which is referred to as the adaptive SFR algorithm (ASFR), that dynamically optimizes subcarrier and power allocations for multicell wireless networks to improve system capacity. The ASFR first finds the subcarrier and power allocations in each cell by using exhaustive search and greedy descend methods and then iteratively repeats among cells until a predefined convergence criterion is satisfied. The theoretical analysis proves the convergence of the ASFR algorithm. Simulation results show that the ASFR achieves a higher system throughput and better cell edge user performance than existing frequency reuse schemes.

Analytic estimation for uplink capacity reduction due to co-channel interference in LTE networks

To achieve high system capacity, most fourth-generation (4G) cellular communication systems, including long term evolution (LTE), tend to adopt aggressive frequency reuse scheme. Although this scheme can increase system capacity, it has a major challenge of suffering severe intercell co-channel interference (CCI), which will reduce cell-edge user throughput and increase outage probability. In this paper, an analytical method is presented for estimating the uplink capacity reduction due to CCI in a cellular LTE network. This method is based on an interference analysis that accounts for random distribution of user locations, propagation shadow fading effect, and user-equipment output power limitations. The results indicate that CCI can cause up to 50 % reduction in throughput for cell-edge users. The proposed method is helpful for estimating the CCI impacts when building a 4G network.

QoS priority-based dynamic frequency band allocation algorithm for load balancing and interference avoidance in 3GPP LTE HetNet

Abstract A 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) system uses the concept of two-tier heterogeneous networks (HetNets), where low-power and short-range femtocells are laid under macrocells to fulfill the quality of service (QoS) requirements of users and to boost overall network capacity. However, co-channel interference is one of the major issues that need to be resolved for the successful deployment of HetNets. To overcome this problem, fractional frequency reuse (FFR) schemes have been proposed that can efficiently utilize the available spectrum. Nevertheless, these schemes waste limited frequency resources owing to their static allocation and lack of following QoS requirements, network loading conditions, and service priority of users. In this paper, a QoS-based dynamic FFR (QoS-DFFR) scheme is proposed that efficiently allocates the non-occupied center-zone frequency bands, i.e., bonus bandwidth (BBW), to cell-edge users by considering their QoS requirements. Consequently, the proposed QoS-DFFR scheme can optimize cell-edge user throughput and sector throughput and reduce co-channel interference by dynamically allocating the BBW to the most demanding cell-edge users. The proposed QoS-DFFR scheme improves performance because of its ability to dynamically allocate the limited portion of the frequency bands based on the service priorities of users. The system-level simulation results show that the proposed QoS-DFFR scheme performs remarkably well in a HetNet environment. Compared with the usual FFR schemes, the proposed scheme almost doubles the cell-edge user's throughput and reduces the user's packet loss rate.

Selective clustering scheme based on user equipment path and frequency reuse scheme for coordinated multi‐point joint processing

Coordinated multi-point (CoMP) – joint processing (JP) is a technique which improves the cell edge user data rate and spectral efficiency. The practical requirements for CoMP-JP in terms of capacity and latency constraints should be solved by considering backhaul network. The possibility of deploying CoMP-JP in practical cellular systems strongly depends on the backhaul network capabilities. The authors propose a selective clustering scheme which is able to selectively form clusters in order to decrease the traffic load of the backhaul network for CoMP-JP. In addition, the authors propose a new frequency reuse scheme for downlink CoMP-JP. The authors are able to decrease intra-cell and inter-cell interference with our proposed frequency reuse scheme. Therefore the authors increase the spectral efficiency and SINR (signal to interference and noise ratio) performance of the system.