Femtocell Cluster Research Articles

Energy Efficiency Using Cloud Management of LTE Networks Employing Fronthaul and Virtualized Baseband Processing Pool

The cloud radio access network (C-RAN) emerges as one of the future solutions to handle the ever-growing data traffic, which is beyond the physical resources of current mobile networks. The C-RAN decouples the traffic management operations from the radio access technologies, leading to a new combination of a virtualized network core and a fronthaul architecture. This new resource coordination provides the necessary network control to manage dense Long-Term Evolution (LTE) networks overlaid with femtocells. However, the energy expenditure poses a major challenge for a typical C-RAN that consists of extended virtualized processing units and dense fronthaul data interfaces. In response to the power efficiency requirements and dynamic changes in traffic, this paper proposes C-RAN solutions and algorithms that compute the optimal backup topology and network mapping solution while denying interfacing requests from low-flow or inactive femtocells. A graph-coloring scheme is developed to label new formulated fronthaul clusters of femtocells using power as the performance metric. Additional power savings are obtained through efficient allocations of the virtualized baseband units (BBUs) subject to the arrival rate of active fronthaul interfacing requests. Moreover, the proposed solutions are used to reduce power consumption for virtualized LTE networks operating in the Wi-Fi spectrum band. The virtualized network core use the traffic load variations to determine those femtocells who are unable to transmit to switch them off for additional power savings. The simulation results demonstrate an efficient performance of the given solutions in large-scale network models.

Stable femtocells cluster formation and resource allocation based on cooperative game theory

In this paper, we address the problem of forming stable groups of femtocells that can reduce the complexity of the resource management and enhance the subscribers’ satisfaction while guaranteeing the service to nearby public users. In a macro-femtocell network, the resource management becomes a very challenging task as the number of deployed femtocells increases. Several strategies of clustering have been proposed to allocate resources in a distributed manner. However, forming stable clusters of femtocells is yet to be addressed. We propose a distributed cluster-based resource allocation framework that consists of three components: (1) a base station selection algorithm for public users that guarantees them a high data rate, (2) a coalition game, where femtocells are grouped into stable clusters to reduce the resource allocation complexity, and (3) a fair resource allocation using the Shapley value to compute the payoff of each cluster member based on Particle Swarm Optimization algorithm. The ε-core concept from game theory is used as the stability criteria to form the clusters. A performance comparison is carried out between the proposed solution and two benchmark models: a centralized approach and a distributed approach with non-stable group formation. Simulation results show that our framework indeed increases the network throughput, provides higher subscribers satisfaction, and higher Jain fairness index for the distribution of resources among the existing users in the femto-tier.

Game theoretical framework for clustering and resource allocation in macro-femtocell networks

We address the femtocell clustering together with the resource allocation in macro-femtocell networks. The clustering schemes allow the implementation of distributed approaches that can run locally within each cluster. Nevertheless, several limitations should be addressed for dense femtocell deployment, such as: lack of clustering schemes that encourage femtocells to grant service to public users and to become cluster members while guaranteeing their subscriber satisfaction, inefficient bandwidth usage due to the lack of bandwidth adaptation per tier when the cluster configuration changes, and lack of power control mechanisms to reduce interference. In this paper, we propose a distributed clustering model based on a cooperative game, where femtocells are encouraged to cooperate by forming clusters and rewarded with resources from macrocell. Our solution consists of: a cluster formation based on a coalitional game among femtocells and the macrocell to determine the subcarrier distribution per tier, a base station selection for public users and a resource allocation algorithm using Particle Swarm Optimization. We compare our solution with a centralized clustering approach and our cooperative clustering model using the well-known Weighted Water Filling resource allocation algorithm. Simulation results show that our proposal obtains throughput values similar to the centralized approach, satisfies the service requirements for both types of users and reduces the interference in comparison with the benchmark models.

A Technique for Cloud Based Clustering and Spatial Resource Reuse and Scheduling of 3D In-Building Small Cells Using CoMP for High Capacity CRAN

In this paper, we propose a technique for cloud coordinated clustering and scheduling of small cells, i.e., femtocells, in CRAN to improve capacity and spectral efficiency in 3D in-building environments. Control-and user-plane of each cell is decoupled. The clustering technique consists of two levels of clustering such that level 1 clustering defines an initial 3D femtocell cluster size. Level 2 clustering defines a cooperating set of femtocells per floor within each level 1 cluster to explore joint transmission coordinated multipoint (CoMP) during off-states of their transmit power. Femtocells are split at the MAC layer, and a mechanism is presented to model the bandwidth and latency fronthaul constraints. We derive the system level aggregate capacity, spectral efficiency, and energy efficiency. We then develop a heuristic algorithm and discuss its scheduler implementation. With numerical and simulation results, we show with an example scenario that the proposed technique can achieve the maximum CoMP capacity gain of 44% per building and 32.15% in overall system level. Finally, we demonstrate that the proposed technique can achieve the performance requirements of 5G cellular systems and point out the significance and further research issues.

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.

Semi-Clustering of Victim-Cells Approach for Interference Management in Ultra-Dense Femtocell Networks

Network densification is seen as a necessary trend in the evolution toward 5G networks to cope with future high-traffic demands. In particular, the use of femtocells seems to be the most feasible solution for hotspot areas where high traffic is concentrated. However, femtocell densification will face a number of technical challenges. Among others, the co-tier interference arises as an old acquaintance with a new significance. In point of fact, the interference characteristics and the role of aggressor and victim depend on a large extent on the density scenario, especially when femtocells share the same channel and operate in a Closed Subscriber Group (CSG) mode. In this regard, identification of victim and aggressor femtocells is a prerequisite to design an effective interference management scheme for ultra-dense femtocell networks (UDFNs). This paper implements a new approach for radio resource utilization and management for victim femtocells in an ultra-dense network environment. The proposed semi-clustering of victim-cell (SCVC) approach focuses mainly on users’ status whether critical or non-critical to categorize victim femtocells and their aggressors. After identifying the victim femtocells, the SCVC scheme semi-cluster each victim femtocell based on the status of each user. Then, it smartly allocates the appropriate radio resources in a dynamic manner, which allows ranging from shared use of resources for critical users to the frequency reuse one for non-critical users, thereby ensuring minimum co-tier interference and enhancement of spectrum efficiency. Simulation results show that our approach outperforms one of the prominent related schemes, namely, femtocell cluster based resource allocation (FCRA), in terms of the mean throughput of critical users, the average capacity of victim femtocells, and the percentage of resource utilization by an approximate average gain of 185%, 64%, and 31%, respectively.

Clustering-based interference management in densely deployed femtocell networks

Deploying femtocells underlaying macrocells is a promising way to improve the capacity and enhance the coverage of a cellular system. However, densely deployed femtocells in urban area also give rise to intra-tier interference and cross-tier issue that should be addressed properly in order to acquire the expected performance gain. In this paper, we propose an interference management scheme based on joint clustering and resource allocation for two-tier Orthogonal Frequency Division Multiplexing (OFDM)-based femtocell networks. We formulate an optimization task with the objective of maximizing the sum throughput of the femtocell users (FUs) under the consideration of intra-tier interference mitigation, while controlling the interference to the macrocell user (MU) under its bearable threshold. The formulation problem is addressed by a two-stage procedure: femtocells clustering and resource allocation. First, disjoint femtocell clusters with dynamic sizes and numbers are generated to minimize intra-tier interference. Then each cluster is taken as a resource allocation unit to share all subchannels, followed by a fast algorithm to distribute power among these subchannels. Simulation results show that our proposed schemes can improve the throughput of the FUs with acceptable complexity.

An Evolutionary Game Theoretic Framework for Femtocell Radio Resource Management

Plug-and-play femtocells will be an integrating part of future cellular networks. Resource management and interference mitigation become challenging, suffering from severely delayed network control in large-scale deployments. We propose a new game theoretic framework, where fast interference suppression is decoupled from the relatively slow frequency allocation process to tolerate the delayed control. The key idea is to cast femtocell clustering as an outer-loop evolutionary game coupled with bankruptcy channel allocation, which drives the cells to spontaneously switch to less interfered clusters. Within each cluster, we design an inner-loop non-cooperative power control game, such that the requirement of prompt control is eliminated. The two loops interact recursively with analytically confirmed stability. Simulations show that our framework can improve the throughput by 13.2% in a network of 200 cells, compared to the prior art. The gain grows further with the network size.

Transmission optimizing on dense femtocell deployments in 5G

SummaryIn the upcoming generation of mobile networks, femtocells will play a major role because they provide cost‐efficient improvement in data rates and coverage. High penetration is expected in the upcoming ultra‐dense 5G networks, increasing the probability of femtocells' clusters. This, in turn, will require interference mitigation techniques to protect nearby non‐subscribed users, especially in weak macrocell signal areas. In this paper, we present a mechanism where multiple femtocells coordinate their transmission to serve multiple non‐subscribed users through hybrid access. First, we introduce an algorithm that determines the spectrum allocation of femtocells' hybrid access. The algorithm aims to compensate for the performance reduction of subscribed users, due to reduced spectrum. For the second step of the mechanism, we introduce a power control algorithm that balances the impact of hybrid access among all the members of the femtocell cluster. First, we investigate the case where only one femtocell operates in hybrid access, and then we refine the power control algorithm by allowing multiple femtocells in the same cluster to operate in hybrid mode and by taking into account the effect that any change in power transmission will have on neighbouring femtocells. Simulations for the evaluation of the hybrid access algorithm compared with closed and other hybrid access schemes show improvement in the throughput of the non‐subscribed users connected to femtocell and the most impacted subscribed users at weak macrocell signal areas and in the fairness of the hybrid access application scheme. Copyright © 2015 John Wiley & Sons, Ltd.

Bandwidth allocation with minimum rate constraints in cluster-based femtocell networks

Inter-femtocell interference becomes serious when femtocells are densely deployed. To mitigate the inter-femtocell interference, this paper proposes a cluster-based bandwidth allocation algorithm. We create femtocell clusters by constructing a weighted interference graph and allocate bandwidth to each cluster based on a Nash bargaining solution (NBS). Simulation results show that the cluster-based bandwidth allocation algorithm can reduce the inter-femtocell interference and meet the minimum rate constraint of each cluster.

Femtocell Subband Selection Method for Managing Cross- and Co-tier Interference in a Femtocell Overlaid Cellular Network

The femtocell overlaid cellular network (FOCN) has been used to enhance the capacity of existing cellular systems. To obtain the desired system performance, both cross-tier interference and co-tier interference in an FOCN need to be managed. This paper proposes an interference management scheme that adaptively constructs a femtocell cluster, which is a group of femtocell base stations that share the same frequency band. The performance evaluation shows that the proposed scheme can enhance the performance of the macrocell-tier and maintain a greater signal to interference-plus-noise ratio than the outage level can for about 99% of femtocell users.

A demand‐based spectrum orthogonalisation scheme for interference avoidance in LTE‐Advanced heterogeneous networks

AbstractSuccessful deployment of femtocells within a macrocell coverage area would be hindered if cross‐layer and co‐layer interference in such heterogeneous networks (HetNets) is not properly mitigated. Through spectrum management, cross‐layer interference between macrocell and femtocell network layers can be avoided by assigning the network layers with orthogonal spectrum bands. However, the orthogonal spectrum assignments in prior works are no longer effective because they may not guarantee the variation of users' traffic demand in HetNets to be satisfied all the time. Therefore, a centralised and dynamic orthogonal spectrum assignment called demand‐based spectrum orthogonalisation (DeBaSO) is proposed in this paper to address the interference issues in downlink of LTE‐Advanced HetNets. In our proposed scheme, the problem of orthogonal spectrum assignment is formulated with the objective to maximise the overall system throughput based on the requirement of physical spectral resources to satisfy the users' traffic demand. Additionally, the co‐layer interference among femtocells is avoided by grouping the adjacent femtocells into different femtocell clusters. To do so, typical model of spatial frequency reuse is exploited in this paper. In this way, femtocells that are grouped within the same cluster can universally reuse the assigned spectrum resource without creating co‐layer interference among them. Numerical results indicate that the proposed scheme achieves a remarkable performance in terms of overall system throughput and spectrum efficiency because the cross‐layer and co‐layer interference is entirely avoided. The achievements prove that DeBaSO scheme overcomes the limitations found in other orthogonal spectrum assignments, which were previously proposed in the literature. Copyright © 2014 John Wiley & Sons, Ltd.

Cross-tier interference management with a distributed antenna system for multi-tier cellular networks

In a multi-tier cellular communication system, the interference from one tier to another, denoted as cross-tier interference, is a limiting factor for the system performance. In spectrum-sharing usage, we consider the uplink cross-tier interference management of heterogeneous networks using femtocells overlaid onto the macrocells. We propose a variation of the cellular architecture and introduce a novel femtocell clustering based on interference cancellation to enhance the sum rate capacity. Our proposal is to use a distributed antenna system (DAS) as an interface to mitigate the cross-tier interference between the macrocell and femtocell tiers. By placing a DAS remote antenna unit (RAU) near a set of femtocells that experience interference from a macrocell user, the DAS can retrieve the interference symbols and feed them back to the femtocells, where each cell can perform interference cancellation when necessary. In addition, the DAS can forward the recovered data to the macrocell base station (MBS); thus, the macrocell user can reduce its transmit power to reach a RAU located closer than the MBS. By distributing the sensor nodes within the macrocell coverage, the proposed scheme can mitigate the cross-tier interference at different locations for several femtocell clusters. Our simulation results show substantial improvement in the network sum rate capacity.

Energy Conservation via Antenna Scheduling in Fiber-Connected Femto Base Stations

We formulated the energy consumption of previously proposed broadband wireless access with fibre-connected massively distributed antennas (BWA-FMDA) architecture under a generalized framework and developed an optimization tool in a femtocell cluster based on coordinated multipoint transmission (femto-CoMP) to maximize energy efficiency by adjusting the number of transmission antennas and controlling transmission power in zero-forcing beamforming. Based on the analysis results, we group every two neighboring antennas in multiple femto-CoMP configurations and proposed a new network configuration scheme that uses antenna scheduling to simultaneously improve spectral and energy efficiency. Compared with standalone femtocells, the proposed scheme is shown in a typical office building to increase energy efficiency by 64 %?~?160 % and spectral efficiency by 2 %?~?36 %. Compared with our previous BWA-FMDA configurations, the new scheme is able to improve energy efficiency by 6 %?~?68 % and spectral efficiency by 15 %?~?55 %. The exact gain depends on network configurations and transmission power levels.

Inter-femtocell interference coordination in 3D in-building scenario

With rapid development of femtocell, dense deployment of femtocells in buildings will become an important study scenario. In this scenario, there exists severe inter-femtocell interference in the same building, which is revealed by our simulations in the 3-dimention (3D) scenario. If this type of interference is not well controlled, services to indoor users are bound to be deteriorated, especially for the femtocell edge users. Motivated by this problem, femto users' received interference model is constructed based on the scenario of 3D femtocell deployment. Then, a graph theory based in-building inter-femtocell coordination scheme is proposed, which includes three phases: establishment of femtocell interference graph, femtocell clustering and frequency resources allocation based on the proposed cluster influence circle. Finally, the simulation results confirm that the proposed scheme improves the femtocell average throughput by 22.4% and 26.2% in comparison with frequency universal reuse scheme and frequency hopping scheme respectively, and ensures the channel demodulation reliability of cell edge femto users.

Handoff Management in Green FEMTOCELL Network

Integrated femtocell/macrocell networks, comprising a conventional cellular network overlaid with femtocells, offer an economically appealing way to improve coverage, quality of service, and access network capacity. The key element to successful femtocells/macrocell integration lies in its selforganizing capability. Provisioning of quality of service is the main technical challenge of the femtocell/macrocell integrated networks, while the main administrative challenge is the choice of the proper evolutionary path from the existing macrocellular networks to the integrated network. In this paper, we propose a new Autonomic Architecture with self organizing capabilities based on the election of a Femtocell cluster Head (FH) for each group of Femtocell APs. The FH will be responsible to dynamically adjust the network overall coverage to save FAP energy and provide better QoS to users. Further it uses an advanced decision algorithm for intelligent handovers. General Terms Wireless Networking, Algorithms.