Dense Deployment Of Femtocells Research Articles

Network capacity improvement in 5G by using dynamic fractional frequency reuse (FFR)

The FFR approach reduces interference between macrocells and small cells/femtocells, which are installed within macrocell’s range. Dense deployment and unplanned installation of small cells and femtocells has a detrimental impact on the performance of the system as a result of the interference. Thus, the FFR concept distributes resources to maintain interference. However, some small cells/femtocells may suffer from shortage resources. In this work, dynamic FFR mechanism has been proposed. The scheme maximizes small cell/femtocell network’s capacity. The strategy aims to boost small cell/femotcell network’s capacity and system throughput. The fundamental goal of this research is to maximize the dedicated radio resources, which are allocated to small cells/femtocells, based on a predetermined cost function. According to the cost function, which is computed for all sub-regions, the proposed dynamic FFR will allocate more radio resources to small cells/femtocells, which suffer from lack resources. The highest degree of the cost function of a certain sub-region would have the largest amount of small cells/femtocells. The sub-region with the lowest cost function would receive fewer radio resources for small cell/femtocell UEs. The throughput is utilized as a metric for the purpose of evaluating the proposed strategy. MATLAB simulation is conducted for that reason. The results show that the proposed technique outperforms the fixed FFR.

Victim Aware AP-PF CoMP Clustering for Resource Allocation in Ultra-Dense Heterogeneous Small-Cell Networks

Heterogeneous networks with dense deployment of femto cells has provided the promising solution to enhance the system throughputs for the next generation wireless communication. When the large number of heterogeneous networks are overlapped, then traditional intercell interface technique failed to mitigate the interference in between the cells. So, to mitigate the interference, it requires advanced approach for improving the cell edge throughputs and spectral efficiency. For this, the paper presents a frame work to allocate the efficient resource among the users in dense networks. We proposed affinity propagation unsupervised learning to form the cluster with center and then regularized the cluster for effectively allocated the resource. Users on the cluster edge has suffering the inter cluster interface, a victim aware and coordination multipoint mechanism is further proposed to allocated the required resources for these victimized users. We analyzed the performance of our proposed framework with proportional fair based criteria. The total throughputs, edge throughput and spectral efficiency of the system are significantly enhanced in our simulation results through this proposed framework.

Energy-Efficient Resource Allocation for OFDMA Heterogeneous Networks

We proposed several energy-efficient resource allocation algorithms for the downlink of an orthogonal frequency-division-multiple-access (OFDMA) based femtocell heterogeneous networks (HetNets). Heterogeneous QoS and fairness in rate are investigated in the proposed resource allocation problem. A dense deployment of femtocells in the coverage area of a central macrocell is considered and energy usage of both femtocell and macrocell users are optimized simultaneously. We aim to maximize the weighted sum of the individual energy efficiencies (WSEEMax) and the network energy efficiency (NEEMax) while satisfying the following: (1) minimum throughput for delay-sensitive (DS) users, (2) fairness constraint for delay-tolerant (DT) users, (3) required constraints of OFDMA systems. The problem is formulated in three different forms: mixed 0–1 integer programming formulation, time-sharing formulation and sparsity-inducing formulation. The proposed resource block (RB) and power optimization problems are combinatorial and highly non-convex due to the fractional form of the objective function, the integer constraint of OFDMA RBs and non-affine fairness. We adopt the successive convex approximation (SCA) approach and transform the problems into a sequence of convex subproblems. With the proposed algorithms, we show that the overall joint RB and power allocation schemes converge to suboptimal solutions. Numerical examples confirm the merits of the proposed algorithms.

Energy-Aware Joint User Scheduling and Power Control for Two-Tier Femtocell Networks: A Hierarchical Game Approach

Femtocells are considered as promising technologies for the next generation wireless networks to improve system capacity and enhance indoor coverage. The dense deployment of femtocells brings a lot of challenges in terms of interference management and energy consumption. To alleviate co-channel interference, we investigate interference management based on hierarchically joint user scheduling and power control in downlink femtocell networks considering the impact of energy cost. Then, we formulate this problem as a Stackelberg game with one leader and multiple followers. Specifically, macro base station and femtocell base stations select their optimal scheduled users and determine the optimal transmission power, based on their own net utilities considering power cost. To obtain the Stackelberg equilibrium (SE) in a distributed manner, a hierarchical and iterative user scheduling and power update framework is proposed. Moreover, we prove that the optimization of user-scheduling and power control can be decoupled in our scheme and the proposed scheme converges to a unique SE under mild conditions. Simulation results are presented to show the convergence and effectiveness of the proposed hierarchical game.

An Energy Efficient Cell Selection Framework for Femtocell Networks With Limited Backhaul Link Capacity

Dense deployment of femtocells improves the network capacity without significantly burdening the operator with huge capital and operational expenditure. However, extremely dense deployment of femtocells comes with the cost of increased cochannel interference and higher energy consumption. Additionally, femtocells burden the existing ADSL/broadband lines by using them as backhaul to connect to the cellular core network. A cell selection scheme defines the criteria on which mobile users associate themselves with base stations. This criteria may include received signal quality, available bandwidth, and energy consumption. Hence, cell selection plays a crucial role in system capacity, load balancing, and energy consumption. In this paper, we provide a framework for femtocell deployment in the urban scenario where interference, energy consumption, and backhaul capacity are major concerns. We first model the energy consumption of base stations, user equipment, and wired backhaul links. Then, we propose an efficient spectrum and power allocation technique to mitigate interference and improve bandwidth utilization in the uplink and downlink, respectively. Finally, we suggest a novel QoS-aware cell selection scheme that assigns mobile users to femtocells considering the capacity improvement obtained per unit increase in energy consumption. The proposed cell selection scheme incorporates the energy consumption of the wired backhaul links and their limited capacity constraint into the cell selection criteria. Our proposed spectrum and power allocation technique, when combined with the proposed cell selection, leads to a significant reduction in energy consumption without any deterioration in the system capacity. Simulation results confirm that our proposed framework has the potential to significantly improve the energy efficiency of the network.

Downlink capacity of OFDMA-CR based 5G femtocell networks

This research work explores small cell densification as a key technique for next generation wireless network (NGWN). Small cell densification comprises space (i.e, dense deployment of femtocells) and spectrum (i.e., utilization of frequency band at large). The usage of femtocells not only improves the spectral efficiency (SE) of the Heterogeneous two-tier networks against conventional approach, but also it alleviates outage probability and enhances the achievable capacity. We yield an analytical framework to establish the density of the femto base station (FBS) to a monotonically increasing or decreasing function of distance or radius, respectively. This ensures the enhanced performance in spectrum sharing Orthogonal Frequency Division Multiple Access (OFDMA) femtocell network models. We also illustrate the influence of active Femto users (i.e., users in femtocells, and they are usually low mobility and located closer to the cell center with less fading), cluster size (i.e., a group of adjacent macrocells which use all of the systems frequency assignments) via simulation results.

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.

Range-Based Scheme for Adjusting Transmission Power of Femtocell in Co-Channel Deployment

In heterogeneous networks, femtocells are introduced to improve the network capacity. However, dense deployment of femtocells leads to undesirable interference, which degrades the performance of the system. The interference can be managed and mitigated based on different approaches such as resource allocation or transmission power control. Controlling the femtocell transmission power is one of the factors that can be considered to alleviate undesirable effect of the interference. Also, it can be used to support auto-configuration conductance of the network. In this work, transmission power auto-configuration approach is proposed. The proposed approach is based on the macrocell transmission power and femtocell coverage. The simulation results depict that the capacity of the network is improved, and the interference is alleviated.

A Simple yet Effective Approach for Interference Mitigation in Tridimensional Two-Tier Femtocell Networks

Dense femtocell deployment in macrocell system is an important tendency in future cellular networks due to the increasing demand in indoor communications, where the cross-tier interference mitigation between the macrocell and femtocells is one of the most critical issues. However, the current studies mostly focus on the cross-tier interference in two-dimensional scenarios with a few works considering the tridimensional cell. In this paper, based on the traditional fractional frequency reuse (FFR) method, we propose a simple yet effective tridimensional frequency reuse strategy to mitigate the cross-tier interference in two-tier femtocell networks. We analyze the performance of the proposed strategy and present the theoretical expression of the interference and the data rate. Moreover, we compare it with the traditional FFR method and the original co-channel method. Simulation results show the huge gain achieved by our proposed strategy and demonstrate its effectiveness on interference mitigation in the tridimensional cell.

Cell selection and resource allocation for sleep mode enabled femtocells with backhaul link constraint

Dense deployment of femtocells in urban regions has proved to be an effective solution to handle ever increasing mobile data demands. Cellular operators are now focusing on extending their network reachability in rural and remote areas by exploring the possibilities for cost effective femtocell deployments. Considering operators’ perspective, capital expenditure due to the deployment of femtocells and associated backhaul links is a major concern. Additionally, operational expenditure due to energy consumption in femtocell and backhaul links is another disquiet. Hence, it is of utmost interest to minimize the capital and operational expenditure to accelerate the rural and remote femtocell deployments. In this paper, we aim to reduce the energy consumption of femtocell deployments by suggesting an energy efficient cell selection scheme complemented by a resource allocation technique. For resource allocation, we suggest a spectrum and power allocation technique based on power spreading to maximize the spectrum efficiency and minimize the transmit power. Additionally, to save energy, we suggest Load Aware Sleep Strategy (LASS) for under-utilized femtocells using Renewal Reward Process. Finally, we propose Energy Efficient Cell Selection (EECS) scheme for mobile users association to femtocells which also incorporates the mobile users’ Quality of Service (QoS) and backhaul link constraints into user association criteria. Obtained results show that our proposed framework for femtocell resource allocation and cell selection can facilitate operators to provide coverage in rural and remote environment in an energy efficient manner.

An energy efficient framework for user association and power allocation in HetNets with interference and rate-loss constraints

Dense deployment of femtocells has proved to be an effective solution to handle increasing demands of indoor mobile data. A femtocell not only helps reducing operational and capital expenditure but also improves the energy efficiency of the network. Femtocells are able to increase spectrum efficiency by manyfold by reusing the available spectrum for indoor users. However, it has been seen that traditional cell selection schemes limit the user count under femtocell. Additionally, dense deployment of femtocells comes with the cost of increased interference to the neighbouring femtocell and macrocell users. In this paper, we first analyse various cell selection schemes to improve user association and resource utilization in femtocells. Then, we focus on improving energy efficiency and throughput of femtocell based cellular networks. For this, we formulate an optimization problem that efficiently reuses macrocell spectrum in femtocells with power control while satisfying macrocell users’ interference and rate-loss constraints.

Enhanced Resource Reservation Technique for Reduced Call Blocking in Femtocell Networks

Femtocell has proved to be a promising technology to enhance indoor coverage and network throughput. Dense deployment of femtocells facilitates efficient offloading of data traffic from the macrocell network to the femtocell network. However, this dense deployment may result in serious inter-femtocell interference. Considering limited coverage radius of the femtocell, frequent handovers is another challenge which may result in excessive call dropping. In order to improve QoS of mobiles users in terms of call blocking ratio, we suggest a predictive resource reservation technique. Our proposed technique first calculates the probability distribution of UEs’ locations in order to optimally deploy femtocells using Active LeZi Algorithm. Then, we use regression-based prediction algorithm (Box-Jenkins Model) to forecast the inter-call arrival and call duration distribution. Finally, we reserve the resources for users in multiple femtocells as to reduce the chances of call dropping. Our proposed technique has shown significantly improve the performance of the network in terms of call blocking, system throughput, and energy efficiency.

Interference Mitigation for Femtocell Networks Via Adaptive Frequency Reuse

The dense deployment of femtocells has brought new challenges for interference management. Flexible and efficient frequency reuse is one of promising approaches to tackling interference among femtocells. In this paper, we propose a semistatic intercell interference coordination (ICIC) scheme called adaptive frequency reuse (AFR). The proposed AFR scheme involves two algorithms, namely, primary subchannel self-configuration (PSC-SC), that served as ICIC, and interference-aware resource allocation, that served as intracell resource allocation. Compared with the no-ICIC scheme (i.e., Reuse 1), the proposed AFR scheme can achieve around 100% gain in terms of spectrum efficiency of cell-edge users with a minimal impact on the spectrum efficiency of cell-center users. Furthermore, the proposed PSC-SC algorithm is characteristic of low signaling overhead and fast convergence, which is very suitable for femtocell networks with constrained-capacity backhaul.

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.

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.

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.

Local Gateway Assisted Handover Key Derivation in Enterprise Femtocell Network

With the dense deployment of femtocells in enterprise femtocell network and the small coverage of femtocells, handover in enterprise femtocell network will be frequent. The general handover key derivation method which is used in handover procedures in LTE is not suitable for handover in this scenario because of its long time cost and the weak security. To solve this problem, this paper has proposed a new local gateway assisted handover key derivation schema in enterprise femtocell network. It can meet the fast derivation and good forward/backward key secrecy requirement of handover key derivation in enterprise femtocell network. The simulation result has verified that the proposed handover key derivation schema works better than the existing method.

Spectrum sharing model for OFDMA macro-femtocell networks

Enhancing the network throughput while supporting non-uniform user distribution and dense femtocell deployment is a challenge in OFDMA networks. Previous research works focus on spectrum partitioning or spectrum sharing with interference managements regardless the user distribution or mobility. In this paper, we propose a spectrum sharing approach that maximises the network throughput using Linear Programming. Power adaptation is performed to mitigate the interference and to guarantee QoS downlink transmissions. Our solution is able to: 1 fairly allocate resources to each macrocell zone taking into account the user distribution; 2 optimally reuse the bandwidth allocated to inner MC zones inside femtocells located in outer zones; 3 optimally determine the serving base station, subcarriers and transmitted power for downlink transmissions taking into account user locations and demands. Simulations are conducted to show a comparison of our solution with two SP approaches with and without partial bandwidth reuse incorporating user mobility.

Coalitional Game Theory for Cooperative Interference Management in Femtocell Networks

Dense deployment of femtocells can cause serious intra-tier interference in femtocell networks. In this paper, a new cooperative interference management approach which allows the femtocell user equipment (FUE) to merge into cooperative groups, that is, coalitions, for the uplink transmissions in a femtocell network is proposed, so as to reduce the intra-tier interference and improve the system performance. Taking into account the power cost for cooperation, we claim that all the FUEs are impossible to merge together, and we formulate the proposed cooperative problem as a coalitional game in partition form with an externality due to the interference between the formed coalitions. To get the solution, a novel distributed coalition formation algorithm that takes advantage of the characteristics of femtocell network and allows the FUEs to interact and individually decide on which coalitions to participate in is proposed. Furthermore, we analyze the convergence and stability of the proposed algorithm. Simulations are conducted to illustrate the behavior and the performance of the proposed coalition formation algorithm among FUEs. Results show that the proposed algorithm can improve the system performance with much lower complexity than some previously proposed coalition formation algorithms.

A survey of handover management in LTE-based multi-tier femtocell networks: Requirements, challenges and solutions

Ubiquitous mobile communication requires increased capacity and appropriate quality guarantee for services. To meet these demands next-generation mobile network operators will deploy small cells next to conventional base station structure intensively to enhance capacity and service coverage for customers. Implementation of seamless handover between first tier (macrocell layer) and second tier (small cells) is one of the key challenges to fulfill the QoS requirements. In this paper we introduce the reader to the details of the handover procedure: information gathering, decision strategies and the base station exchange process. All these three phases face difficulties in multi-tier networks. High dense femtocell deployment makes handover related information gathering very hard, efficient handover decision mechanisms are vital to reduce the number of unnecessary handovers and avoid ping-pong effect. Last but not least base station exchange has to be accelerated to achieve appropriate system performance. Next a comprehensive survey of state of the art handover optimization solutions in 3GPP LTE/LTE-A Home eNodeB handover management is presented which includes the actual version of 3GPP LTE/LTE-A HeNB handover procedure.