Fractional Frequency Reuse Scheme Research Articles

2-Layer Interference Coordination Framework Based on Graph Coloring Algorithm for a Cellular System With Distributed MU-MIMO

In this study, a cellular system with a large-scale distributed multi-user multi-input multi-output (MU-MIMO) is considered, in which a large number of distributed antennas are deployed spatially over each base station coverage area (cell) and user clusters are formed in each cell to perform cluster-wise distributed MU-MIMO in parallel. In such a cellular system, the intercell and intracell interferences coexist and limit the link capacity. In this study, a 2-layer interference coordination (IC) framework that can effectively mitigate the two types of interferences simultaneously is proposed. In the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> layer, the intercell IC is performed in a centralized manner by the non-real-time (non-RT) radio access network intelligent controller (RIC), and then in the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> layer, under the condition of the results in the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> layer, intracell IC is done by each near-RT RICs in a decentralized manner. Furthermore, a restricted conditional graph coloring algorithm (RCGCA) suitable for this 2-layer IC framework is proposed. The proposed RCGCA is designed to be applied on a partial pre-colored graph, such that when it is applied in the 2-layer IC framework, it satisfies the requirement that the 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> layer coloring must be applied under the condition of the pre-coloring results of the 1 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">st</sup> layer. In addition, by restricting the total number of colors, the RCGCA can tradeoff between improving the capacity due to interference mitigation and degrading the capacity due to bandwidth partition, thereby maximizing the link capacity. We compare the link capacity achievable by the proposed 2-layer IC framework based on RCGCA with that achievable by the well-known fractional frequency reuse (FFR) scheme, no interference coordination case, fully centralized framework, and fully decentralized framework. Computer simulations confirm that our proposed 2-layer IC framework based on RCGCA can significantly improve the link capacity.

Auction Mechanism-Based Sectored Fractional Frequency Reuse for Irregular Geometry Multicellular Networks

Modern cellular systems have adopted dense frequency reuse to address the growing amount of mobile data traffic. The system capacity is improved accordingly; however, this is at the cost of augmented Inter-Cell Interference (ICI). Recently, Fractional Frequency Reuse (FFR) has emerged as an efficient ICI management scheme in Orthogonal Frequency-Division Multiple Access (OFDMA)-based cellular systems. However, the FFR scheme that leads to optimized spectrum allocation for individual users in the irregular geometry networks is not considered in the literature. Meanwhile, in the practical wireless scenario, the users are non-cooperative and want to maximize their demands. A game-theoretic Auction Mechanism-based Sectored-FFR (AMS-FFR) scheme is proposed in this paper to optimally distribute the bandwidth resources to the individual users in the realistic multicellular network deployment. In the proposed auction mechanism, the Base Station (BS) acts as an auctioneer and is the owner of sub-carriers. The users are permitted to bid for a bundle of sub-carriers corresponding to their traffic requirements. The Monte Carlo simulation results show that the presented AMS-FFR scheme outperforms the prevailing FFR schemes in terms of achievable throughput by 65% and 46% compared to the basic FFFR and dynamic FFR-3 schemes, respectively. Moreover, the average sum rate along with the user satisfaction is significantly increased while considering a full traffic load.

Promoting fractional frequency reuse performance for combating pilot contamination in massive multiple input multiple output

&lt;span&gt;Massive multiple-input multiple-output (MIMO) improves spectrum efficiency by increasing the capacity of the wireless structure. Therefore, massive MIMO is promising for fifth generation (5G) wireless communications. In massive MIMO, channel estimation is a crucial part that should achieve reliable performance. Pilots are sent from the end-users to be used for estimating the channel. However, the problem of interference in pilot contamination affects the performance for cell-edge users. Specifically, pilot contamination appears when the same pilot sequence is utilized at the same time by more than one terminal. This lead to an inaccurate estimation of the channel. Consequently, the decoded data will not be reliable. For mitigating these pilot contamination effects, an enhanced fractional frequency reuse (eFFR) scheme is proposed that uses an algorithm in the allocation of pilot sequences to end users’ devices based on the locations of the users from the target base station (BS). The simulation results exhibit that the proposed scenario outweighs the traditional FFR within both signal to interference, and noise ratio (SINR), and capacity. Consequently, the suggested scenario enhances the performance of more than 80% of the cell terminals and the other 20% of the terminals have a slightly lower performance compared to the FFR.&lt;/span&gt;

Hungarian Mechanism based Sectored FFR for Irregular Geometry Multicellular Networks

The growing demands for mobile broadband application services along with the scarcity of the spectrum have triggered the dense utilization of frequency resources in cellular networks. The capacity demands are coped accordingly, however at the detriment of added inter-cell interference (ICI). Fractional Frequency Reuse (FFR) is an effective ICI mitigation approach when adopted in realistic irregular geometry cellular networks. However, in the literature optimized spectrum resources for the individual users are not considered. In this paper Hungarian Mechanism based Sectored Fractional Frequency Reuse (HMS-FFR) scheme is proposed, where the sub-carriers present in the dynamically partitioned spectrum are optimally allocated to each user. Simulation results revealed that the proposed HMS-FFR scheme enhances the system performance in terms of achievable throughput, average sum rate, and achievable throughput with respect to load while considering full traffic.

Efficient radio resource allocation scheme for 5G networks with device-to-device communication

&lt;p&gt;A vital technology in the next-generation cellular network is device-to-device (D2D) communication. Cellular user enabled with D2D communication provides high spectral efficiency and further increases the coverage area of the cell, especially for the end-cell users and blind spot areas. However, the implementation of D2D communication increases interference among the cellular and D2D users. In this paper, we proposed a radio resource allocation (RRA) algorithm to manage the interference using fractional frequency reuse (FFR) scheme and Hungarian algorithm. The proposed algorithm is divided into three parts. First, the FFR scheme allocates different frequency bands among the cell (inner and outer region) for both the cellular and the D2D users to reduce the interference. Second, the Hungarian weighted bipartite matching algorithm is used to allocate the resources to D2D users with the minimum total system interference, while maintaining the total system sum rate. The cellular users share the resources with more than one D2D pair. Lastly, the local search technique of swapping is used for further allocation to minimize the interference. We implemented two types of assignments, fair multiple assignment, and restricted multiple assignment. We compared our results with existing algorithms which verified that our proposed algorithm provides outstanding results in aspects like interference reduction and system sum rate. For restricted multiple assignment, 60-70% of the D2D users are allocated in average cases.&lt;/p&gt;

Study of Handover Techniques for 4G Network MIMO Systems

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

Multi-Tier Variable Height UAV Networks: User Coverage and Throughput Optimization

Unmanned aerial vehicles (UAVs) are increasingly considered to act as base stations (BSs) for the future wireless networks. Some of the crucial UAV-assisted network design challenges are the network coverage, throughput, and energy efficiency. Therefore, fast, low-complexity, and efficient UAV placement and resource allocation strategies are imperative. This paper presents a novel variable height multi-UAV deployment strategy to exploit the 3D flexibility of UAVs as BSs. We propose a multi-tier variable height UAV-based network deployment and compare its performance with the state-of-the-art equal height deployment. Height optimization is performed to deliver energy efficiency and throughput maximization for each cell. The results show that our proposed method is more energy-efficient in a multi-cell UAV network than the most widely used height optimization method in the literature. In UAV networks, users at the cell edges can receive very poor signal-to-interference-plus-noise ratio (SINR) levels due to interfering UAVs. To cope with this problem, we adopt a fractional frequency reuse (FFR) scheme to compensate low SINR levels. We optimize the SINR threshold corresponding to each cell to maximize their spectral efficiency (SE), thereby improving the network’s area spectral efficiency (ASE). The numerical results show that the proposed deployments provide significant gains in coverage density, SINR coverage probability, rate coverage, and ASE compared to equal height benchmark scheme. As the number of UAVs increases, the number of tiers need to increase to preserve the rate coverage of the network. Moreover, the performance of the proposed variable height model is expected to converge to that of equal height cellular design for a large number of UAVs.

Fractional Frequency Reuse with Enhanced Scheduling Strategies

Heterogeneous networks are used to meet both capacity and coverage demands in a cellular network. As the frequencies are reused due to the limited spectrum availability, there exists co-channel interference (CCI) between the high power and low power nodes in such networks apart from the CCI between high power nodes. Inter cell interference coordination (ICIC) is a big challenge towards heterogeneous network deployments since users located at the cell range expansion (CRE) area are more vulnerable to stronger interference caused by the signals from the high power nodes. To enhance capacity, achieve good user experience and improve spectral efficiency interference management techniques like fractional frequency reuse (FFR) with enhanced scheduling strategies and ICIC using expectation maximization algorithm are proposed to mitigate the effects of the CCI. The resource allocation in FFR is done for the users in the cell center (full reuse) and CRE (partial reuse) regions based on the optimum post processing signal to interference plus noise ratio threshold with different schedulers in the two regions. It is shown that a particular combination shows the best throughput performance for the proposed enhanced FFR scheme.

An improved water-filling algorithm based on power allocation in network MIMO

Inter-Cell Interference (ICI) could affect the performance of the LTE-Advanced (LTE-A) system and can be evaluated according to the user’s Signal to Interference and Noise Ratio (SINR). Owing to this, the power and frequency allocation schemes can be utilized in order to attain an optimum trade-off within the obtained SINR and the resulting interference. In this study, power allocation was integrated into the Dynamic Fractional Frequency Reuse (DFFR) scheme and Network MIMO (NetMIMO) to reduce ICI and enhance the performance of LTE-A downlink. Moreover, this study focuses on the design and development of a novel power allocation algorithm, which is an extension to the previous Improved Water-Filling algorithm (IWF), namely, Low-Complexity Improved Water-Filling algorithm (LC-IWF). Results indicated a reduction in computations and enhancement in interference rejection performance in comparison to the existing algorithms by removing the Lagrange multiplier and water level. Moreover, simulation results revealed that the proposed algorithm enhances the throughput and fairness of up to 20% and 25%, respectively. Furthermore, the power consumption was reduced by 41% and the running time was 5–10 times faster than the IWF algorithm while attaining the best solution. The proposed power allocation algorithm provided a significant improvement in the performance of the NetMIMO LTE-A system, which can be extended for future 5G networks.

An Analytical View of ASE for Multicell OFDMA Networks Based on Frequency-Reuse Scheme

This paper presents efficient interference-mitigation techniques, such as fractional frequency reuse (FFR) and soft frequency reuse (SFR) schemes, in multicell orthogonal frequency division multiple access networks under the composite multipath fading environment, where Rayleigh fading is superimposed over log-normal shadowing. We begin by outlining the obtained explicit expressions of area spectral efficiency in down-link transmission for both FFR and SFR schemes. The theoretical result are shown to be very accurate with their simulated counterparts using Monte Carlo simulations.

Modelling and performance analysis of FFR‐aided two layer aerial‐terrestrial network

Exploiting aerial base stations (A-BSs) in conjunction with terrestrial base stations (T-BSs) is an effective solution to provide uniform coverage everywhere, and anytime. However, the addition of A-BSs in an existing terrestrial network would intensify the inter-cell interference to user equipment, leads to a degraded signal-to-interference-ratio. There is a need to exploit inter-cell-interference-coordination (ICIC) scheme in such aerial-terrestrial network. Further, the aerial-terrestrial network requires a multi-layer environment to be modelled in many scenarios. In this study, the authors propose fractional frequency reuse (FFR) scheme as an ICIC scheme for two-layer aerial-terrestrial network. The analytical expression of coverage probability and average rate are derived for the proposed scheme, and compare it with the scheme, where no ICIC is considered in aerial-terrestrial network, and conventional scheme, where only T-BSs are considered. It is shown that the proposed scheme outperforms the no ICIC scheme and conventional scheme. Simulation results are shown to support their analytical results.

Irregular Geometry Based Sectored FFR Scheme for ICI Mitigation in Multicellular Networks

Future Cellular Systems are aiming aggressive frequency reuse in response to the exponential increase in the data traffic demand. The system capacity boosted accordingly, however, at the expense of increased Inter Cell Interference (ICI). Fractional Frequency Reuse (FFR) is an effective ICI mitigation approach, however, mostly analyzed with regular geometry model in literature. In this paper, Irregular Geometry based Sectored-FFR (IGS-FFR) scheme is proposed for ICI mitigation in the realistic irregular geometry cellular networks. The proposed scheme realize full frequency utilization by dynamic spectrum partition while considering heterogeneous traffic demand. Moreover, the performance of high order sectoring in the cell edge region is investigated. It is shown that the proposed IGS-FFR scheme outperform the existing approaches in terms of achievable throughput, average sum rate and user satisfaction while considering full traffic load.

Interference reduction in long‐term evolution‐advanced by frequency and power domains

Mobile communication systems are growing steadily. In addition, users require better quality of service and large coverage offering a high quality of signal. To meet these challenges, a new concept named heterogeneous network (Het‐Net) has been adopted. The Het‐Net is a network deploying different types of cells (from a macro shape up to femto ones). Operators look to improve the performance of their networks and to remedy the problem of areas with low coverage. However, the coexistence of these different cell models causes interference at the downlink which can affect offered signal's quality. This interference results therefore performance degradation. Therefore, a novel intercell interference mitigation scheme, based on frequency and power domain, is proposed in order to reduce interference in Het‐Net long‐term evolution‐advanced. In frequency domain, the macrocell has to allocate a frequency band by using fractional frequency reuse scheme and the femtocells choose subbands that are not used in the macrocell sector to reduce interference. On the other hand, the small cells transmitted powers are controlled for limiting the interference imposed by it on the other users in the cell area. Simulation results show that the proposed scheme enhances the signal to interference plus noise ratio of macro and femto users and the overall throughput in the network.

Distance-Constrained Outage Probability Analysis for Device-to-Device Communications Underlaying Cellular Networks with Frequency Reuse Factor of 2

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.

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.

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.

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.

Interference Management Based on RT/nRT Traffic Classification for FFR-Aided Small Cell/Macrocell Heterogeneous Networks

Cellular networks are constantly lagging in terms of the bandwidth needed to support the growing high data rate demands. The system needs to efficiently allocate its frequency spectrum such that the spectrum utilization can be maximized while ensuring the quality of service (QoS) level. Owing to the coexistence of different types of traffic (e.g., real-time (RT) and non-real-time (nRT)) and different types of networks (e.g., small cell and macrocell), ensuring the QoS level for different types of users becomes a challenging issue in wireless networks. Fractional frequency reuse (FFR) is an effective approach for increasing spectrum utilization and reducing interference effects in orthogonal frequency division multiple access networks. In this paper, we propose a new FFR scheme in which bandwidth allocation is based on RT/nRT traffic classification. We consider the coexistence of small cells and macrocells. After applying FFR technique in macrocells, the remaining frequency bands are efficiently allocated among the small cells overlaid by a macrocell. In our proposed scheme, total frequency-band allocations for different macrocells are decided on the basis of the traffic intensity. The transmitted power levels for different frequency bands are controlled based on the level of interference from a nearby frequency band. Frequency bands with a lower level of interference are assigned to the RT traffic to ensure a higher QoS level for the RT traffic. RT traffic calls in macrocell networks are also given a higher priority compared with nRT traffic calls to ensure the low call-blocking rate. Performance analyses show significant improvement under the proposed scheme compared with conventional FFR schemes.