Deployment Of Heterogeneous Networks Research Articles

Cost- and energy-efficient backhaul options for heterogeneous mobile network deployments

Heterogeneous networks (HetNets) have the potential to cater for the capacity requirements of mobile broadband services at reduced cost and energy consumption levels. One key aspect in HetNets is the role of the backhaul. More specifically, it is crucial for a mobile operator to understand the impact of specific technological and architectural upgrades in the mobile backhaul network on the capital and operational expenditure (i.e., CAPEX and OPEX). This paper proposes a comprehensive methodology that can be used to analyze the total cost of ownership of a number of backhaul options based on fiber, microwave, and copper technologies. The study considers both a Greenfield and a Brownfield scenario and takes into account the mobile broadband capacity requirements for the time period between years 2015 and 2025. From the results presented in the paper it can be concluded that even though microwave and fiber will be predominately used in the future, the possible migration paths leading to such fiber- and microwave-based backhaul scenarios might be different, depending upon factors such as spectrum and license costs, time to deployment, availability of equipment, and required quality of service levels.

Energy-aware deployment of dense heterogeneous cellular networks with QoS constraints

The base station (BS) configuration is a key factor to improve energy efficiency (EE). In this paper, we focus on designing the network deployment parameters (i.e., BS densities) for biased $K$-tier heterogeneous cellular network (HCN) with quality of service (QoS) provisioning. Using appropriate approximations, we derive the closed-form expressions of optimal BS density across all tiers to minimize the area power consumption (APC) by applying the stochastic geometry theory, while satisfying the users QoS requirements. These results are used to obtain some new insights into the EE performance of biased HCN deployment. With the aid of this approach, the best type of BSs to be deployed or switched off for energy saving purposes can be identified from the perspectives of BS transmission power. More precisely, if the BS transmission power ratio between an arbitrary pair of tiers of $K$-tier HCN, e.g., the small cell BS and macro BS tiers, is higher than a threshold which is a function of path loss exponent, bias factor and power consumption, the small cell BSs are preferred. The opposite situation takes place otherwise. Furthermore, it is also shown that, compared to the unbiased HCN scenario, significant energy savings are possible by appropriately biasing the HCN and optimizing the BS density, subject to the QoS constraints among all tiers.

An Optimized CoMP Transmission for a Heterogeneous Network Using eICIC Approach

Heterogeneous network deployment is considered to be among the most promising approaches to meet the demand for increasing communication capacity. The concept is that of increasing the number of cells while reducing their size to provide different layers of coverage. This paper proposes a coordinated method to face the interlayer and intralayer interference caused by the overlapping of heterogeneous cells. The aim is to exploit the benefits of both enhanced intercell interference coordination (eICIC) and coordinated multipoint (CoMP) approaches and to limit, at the same time, their drawbacks by means of their optimized joint use. The idea devised here is to build an ad hoc CoMP system on top of a basic eICIC mechanism. Therefore, the analysis focuses on the dynamic selection of users and cells involved in CoMP operations, with the goal of minimizing the unfulfilled data rate requests (UDRRs). Due to the computational complexity of the optimal solution, we propose a heuristic procedure and validate its accuracy by providing a comparison with the optimal numerical solution. In particular, our results show that the proposed method outperforms other benchmark solutions in terms of UDRRs and signaling overhead.

On the deployment of large-scale wireless sensor networks considering the energy hole problem

Heterogeneous sensor networks have been proposed to address some fundamental limits and performance issues present in homogeneous Wireless Sensor Networks (WSNs). Questions such as the number of high-end sensors should be used, and how to deploy them, need proper assessment. In this work, we propose a novel model capable of representing a wide variety of scenarios, from totally random to planned stochastic node deployment in both homogeneous and heterogeneous sensor networks. In particular, this model encompasses networks with the characteristics of small-world networks. Using only about 3% of high-end sensors, and deploying nodes by using the slightly attractive model defined herein, we observe improved characteristics of the network topology, such as: (i) low average path length, (ii) high clustering coefficient, and (iii) improved relay task distribution among sensors. We also provide a guide for deploying nodes in order to improve the network lifetime, showing that the aforementioned model can be used to diminish the energy hole effect. Moreover, we evaluate a topological metric, namely Sink Betweenness, suitable for characterizing the relay task of a node.

Energy savings through self-backhauling for future heterogeneous networks

Mobile operators face continuous challenge of enhancing network capacity and coverage so as to meet demand for ubiquitous high-speed mobile data connectivity. Unfortunately, these enhancements are typically accompanied by increased burden of network energy consumption. Heterogeneous network (HetNet) deployments of a large number of low power small base stations (SBS) to complement existing macro base stations is an approach that increases network capacity but potentially reduces overall network energy consumption. The SBS backhaul links in HetNets present a significant powering burden. In this paper, we show how self backhauling of SBS can reduce overall network power demand. A backhaul-energy consumption model is developed and used to investigate the energy efficiency of different backhauling options. We note that significant energy savings could be achieved through the use of self-backhauling when compared with the conventional microwave backhauling. The results presented would provide guidelines for energy- and cost-efficient backhaul implementation for future HetNets.

A Framework for Co-Channel Interference and Collision Probability Tradeoff in LTE Licensed-Assisted Access Networks

Small cell deployment in heterogeneous networks, whereby small cell base stations (SBS) are deployed alongside traditional macro-cell base stations, is a proven solution for enhancing spatial frequency reuse across licensed spectrum in long-term evolution (LTE) networks. In order to mitigate the shortage of licensed spectrum resources, licensed-assisted access (LAA) has been introduced to allow LTE SBSs to share the unlicensed channel with WiFi nodes. As such, a complex yet interesting optimization problem results from the joint utilization of licensed and unlicensed spectrum resources by the SBSs to meet the quality-of-service (QoS) requirements of small cell users (SUEs). In this paper, we highlight the fundamental tradeoff induced by the SBSs between the amount of co-channel interference (CI) resulting from the reuse of licensed spectrum resources and the collision probability (CP) imposed on the co-existing WiFi nodes due to the sharing of unlicensed spectrum resources in such a coexisting LTE LAA-WiFi heterogeneous network deployment. We find that this fundamental tradeoff can be analyzed by developing a power allocation rule with double water-filling lines and the complete set of Pareto optimal solution can be achieved by the weighted Tchebycheff method. Our simulation results show that the proposed joint resource allocation algorithm can achieve a flexible and suitable tradeoff between the licensed spectrum CI and the WiFi CP according to the QoS requirements of SUEs in LTE LAA networks.

Hybrid channel gain prioritized access‐aware cell association with interference mitigation in LTE‐Advanced HetNets

SummaryLTE‐Advanced heterogeneous networks deployment is meant to address the increasing demand for quality of service, high data rates and coverage extension. Load balancing is among the primary challenges, especially when the user equipments (UEs) associate with diverse transmission power network tiers using received signal strength. The low‐power network tier's spectrum will be underutilized, and UEs associated with them will be inflicted by interference from the high‐power network tier. The proposed hybrid channel gain prioritized access (HCGPA)‐aware cell association scheme stresses the importance of combined metrics with interference mitigation to simultaneously achieve load balancing and enhance performance among the network tiers. The high‐priority UEs associate with the tier that gives the maximum channel gain being higher than a given threshold. While the low‐priority UEs association is based on the maximum joint metrics (channel gain, channel access probabilities of low‐priority UEs and high‐priority UEs). The HCGPA scheme has 1.72 times the number of UEs connected to low‐power networks, 8% better load balancing fairness, compared with the conventional reference signal receive power and RSRP + 6 dB bias cell associations. Although the susceptibility of HCGPA to interference led to the poor signal to interference to noise ratio (SINR) performance of the cell‐edge UEs, the cell‐centre UEs exhibited the best spectral efficiency performance. Copyright © 2016 John Wiley & Sons, Ltd.

Spectrum management issues for heterogeneous networks in commons spectrum

Purpose The purpose of this paper is to analyse some of the spectrum management policy implications of an evolving set of wireless technologies. Specially, deployment of heterogeneous networks (HetNets) as part of the rollout of long-term evolution networks and their expected use as the heart of next-generation services raises the question as to whether such networks should lead to any spectrum management policy changes. Design/methodology/approach The paper describes the use and variety of HetNets when using licensed and unlicensed or commons spectrum. Findings The paper demonstrates that there is little need to change current spectrum licensing regimes to deal with these networks in a licensed spectrum. However, it also shows that the deployment of HetNets other than WiFi in an unlicensed spectrum creates an information asymmetry, which means that spectrum regulators will find assessment of spectrum demand more difficult. The paper also highlights the problem facing spectrum regulators when there is a potential for interference to unlicensed services which are widely deployed but have no right to protection from interference. Practical implications Spectrum regulators will need to understand the extent to which an unlicensed spectrum is being used by mobile network operators to deliver wireless broadband services. This understanding is needed to be able to address potential interference with other services using an unlicensed spectrum and to be able to forecast spectrum demand. Originality/value The development of technologies that are designed to be used by existing mobile network operators for the delivery of wireless broadband services using an unlicensed spectrum creates novel regulatory challenges. This paper reviews some of these.

A Flexible and Cost-Effective Heterogeneous Network Deployment Scheme for Beyond 4G

The network capacity has to be maximized to support the ever-increasing data traffic demand. One of the potential outcomes to enhance the network capacity is to enhance the spectral efficiency per unit area by expanding the serving node densities. This is unreasonable on account of present Macro evolved node B (eNB) for which site acquisition is expensive. The idea of heterogeneous network (HetNet) and multi-hop relay (MHR) are extremely prominent in long-term evolution (LTE) standard, where small cells are deployed along with Macro cell. Small cells are more suitable solution for the coverage and traffic issues experienced by Macro cell users. Unfortunately, HetNet deployment is not specified in any of the standards. The network operators have been managing tremendous investments for cellular infrastructures. Because of the high cost and lack of radio resources, a precise and productive HetNet deployment seems uttermost important. In this work, a flexible four-stage fuzzy logic-based HetNet deployment scheme is proposed, which deploys mix of Macro-eNB, Micro-eNB and relay station (RS) by considering capacity, coverage and cost factors. The proposed scheme identifies the required number of eNBs, their types and deployment locations to offer the expected coverage in a cost-effective way. The simulation results demonstrate that our proposed scheme is more flexible and offers improved performance in terms of system cost and power ratio than the conventional HetNet deployment schemes.

Cost-Efficient Optimization of Base Station Densities for Multitier Heterogeneous Cellular Networks

Heterogeneous cellular networks have emerged as the primary solution for overwhelming traffic demands. This study addresses the architecture optimization of multitier open-access downlink heterogeneous cellular networks. A distinguishing feature of this work is that the transmission requirements of mobile users and the profit requirements of operators are all considered. Spatial throughput is maximized under practical constrains on the network deployment cost and traffic loads of individual tiers. By using stochastic geometry, the problems of optimizing the densities of base stations (BSs) in different tiers are shown to be linear-fractional programming that can be further transformed into linear programming by employing Charnes–Cooper transformation. The linear-fractional programming can then be solved efficiently. For a two-tier network, the optimal BS densities are derived in closed form by using the graphical method. Our results indicate that enlarging the densities of BSs may not always improve network throughput and that the optimal densities of each tier exist to satisfy the communication demands of mobile users and the profit requirements of operators. Numerical results demonstrate the significant throughput gain from the optimal deployment of multitier heterogeneous cellular networks.

Survey on Algorithms and Strategies for Mobility Enhancement under Heterogeneous Network (HetNet) Deployment Circumstances

Cell selection/reselection and handover (HO) are important mobility features and challenges of wireless cellular system. When network topology transforms from macro-only to heterogeneous network (HetNet) deployment, the imbalance of transmitted power and coverage area of different kinds of cells in HetNet introduce more challenges to those two important processes. In this paper, we investigate and elaborate some new algorithms and strategies to meet those challenges. On cell selection/reselection, there are two directions in associating more UEs with small cells, one is RSRP-based by introducing a empirical bias to expand small cells’ coverage area, the other is fairness-based to maximize the system throughput and usage of resources. As to more important and difficult HO process, the proposed methods include optimizing the parameters of event A3, handling time to trigger(TTT), optimizing HO process and utilizing inter-cell interference coordination algorithm(ICIC) etc, to maximize the usage of capability of deployed small cell. The presented new algorithms and strategies promise specific performance improvement with introducing receivable time and computing complexity.

A Multiband OFDMA Heterogeneous Network for Millimeter Wave 5G Wireless Applications

Emerging fifth generation (5G) wireless networks require massive bandwidth in higher frequency bands, extreme network densities, and flexibility of supporting multiple wireless technologies in order to provide higher data rates and seamless coverage. It is expected that utilization of the large bandwidth in the millimeter-wave (mmWave) band and deployment of heterogeneous networks (HetNets) will help address the data rate requirements of 5G networks. However, high pathloss and shadowing in the mmWave frequency band, strong interference in the HetNets due to massive network densification, and coor- dination of various air interfaces are challenges that must be addressed. In this paper, we consider a relay-based multiband orthogonal frequency division multiple access (OFDMA) HetNet in which mmWave small cells are deployed within the service area of macro cells. Specifically, we attempt to exploit the distinct propagation characteristics of mmWave bands (i.e., 60 GHz- the V-band - and 70-80 GHz -the E-band-) and the Long Term Evolution (LTE) band to maximize overall data rate of the network via efficient resource allocation. The problem is solved using a modified dual decomposition approach and then a low complexity greedy solution based on iterative activity selection algorithm is presented. Simulation results show that the proposed approach outperforms conventional schemes.

Resource Allocation for Energy Efficiency Optimization in Heterogeneous Networks

Heterogeneous network (HetNet) deployment is considered a de facto solution for meeting the ever increasing mobile traffic demand. However, excessive power usage in such networks is a critical issue, particularly for mobile operators. Characterizing the fundamental energy efficiency (EE) performance of HetNets is therefore important for the design of green wireless systems. In this paper, we address the EE optimization problem for downlink two-tier HetNets comprised of a single macro-cell and multiple pico-cells. Considering a heterogeneous real-time and non-real-time traffic, transmit beamforming design and power allocation policies are jointly considered in order to optimize the system energy efficiency. The EE resource allocation problem under consideration is a mixed combinatorial and non-convex optimization problem, which is extremely difficult to solve. In order to reduce the computational complexity, we decompose the original problem with multiple inequality constraints into multiple optimization problems with single inequality constraint. For the latter problem, a two-layer resource allocation algorithm is proposed based on the quasiconcavity property of EE. Simulation results confirm the theoretical findings and demonstrate that the proposed resource allocation algorithm can efficiently approach the optimal EE.

High-energy efficient deployment scheme of small base stations for heterogeneous network

For small-cell deployment in heterogeneous cellular networks, we investigate the impact of the numberof small base stations (BSs) and the transmit powers on network energy efficiency and propose a joint optimizationdeployment scheme. In this scheme, we first consider the constraints of network coverage and then use an iterativescheme to maximize the network EE (energy efficiency). Simulation results show that there exists an optimalnumber of small BSs and transmit power that can not only maximize network EE but also satisfy the constraints.Further, the proposed scheme is more effective than exhaustive searching with respect to the complexity of thealgorithm, and the network EE of our scheme has significant gains compared with the traditional scheme whenconsidering only the optimization for the number of small BSs.

Energy efficiency optimization-oriented control plane and user plane adaptation with a frameless network architecture for 5G

In order to fully explore the merits of the multi-tier heterogeneous network (HetNet) and ultra-dense small cell deployments, the evolution of the cellular network architecture is on the way. Based on the frameless network architecture, this paper proposes the control plane (CP) and user plane (UP) adaptation strategy to improve the system energy efficiency (EE). In this paper, we give a three-step system EE optimization with constraints on the CP/UP adaptation. We optimize the system EE via CP and UP construction and adaptation while guaranteeing the user quality of service (QoS). In the first step, the CP construction and adaptation scheme is proposed through the Voronoi Diagram with EE improvements. In the second step, by jointly allocating the AE and subchannel resources, we construct the on-demand user-centric UP. In the last step, based on the UP construction from the second step, we adjust each UP to optimize the EE performance. This is achieved by employing game theory. Furthermore, we verify the existence and uniqueness of the Nash Equilibrium for the non-cooperative game model with pricing. Finally, the system-level simulation results show that, with constraints on the QoS of the users, the system EE performances are improved.

Technical advances in the design and deployment of future heterogeneous networks

The trend in wireless communications systems is the enhancement of the network infrastructure with the introduction of small cells, where a specific geographical area is served by low-range, low-power access points. The result is the creation of a heterogeneous topology where macrocells coexist with a variety of small-cell types. In this editorial article we briefly summarize the recent technical advances in the design and deployment of future heterogeneous networks addressed in the papers that compose this special issue. In particular the following aspects are considered: the design of interference and radio resource management algorithms, the analysis of the energy efficiency and power control issues in heterogeneous networks, the concept of coordination in small cell networks, key backhaul aspects of HetNets, deployment issues and overall management strategies.

Self-Resource Allocation and Scheduling Challenges for Heterogeneous Networks Deployment

A reliable solution for meeting the high demand of throughput in areas called hotspots is the heterogeneous network. Heterogeneous networks are different depending on their coverage, their type of radio access technique and the way there are connected to the core network. This paper proposes a novel algorithm for semi-coordinated resource allocation and scheduling based on mobile positioning information, game theory and reinforcement learning technique. The capabilities of such an approach to support the practical deployment of heterogeneous networks is analyzed. Further, a reasoning strategy is proposed to justify the choice of Wi-Fi versus other small cell technologies from a practical deployment viewpoint.

Dynamic Heterogeneous Learning Games for Opportunistic Access in LTE-Based Macro/Femtocell Deployments

Interference is one of the most limiting factors when trying to achieve high spectral efficiency in the deployment of heterogeneous networks (HNs). In this paper, the HN is modeled as a layer of closed-access LTE femtocells (FCs) overlaid upon an LTE radio access network. Within the context of dynamic learning games, this work proposes a novel heterogeneous multiobjective fully distributed strategy based on a reinforcement learning (RL) model (CODIPAS-HRL) for FC self-configuration/optimization. The self-organization capability enables the FCs to autonomously and opportunistically sense the radio environment using different learning strategies and tune their parameters accordingly, in order to operate under restrictions of avoiding interference to both network tiers and satisfy certain quality-of-service requirements. The proposed model reduces the learning cost associated with each learning strategy. We also study the convergence behavior under different learning rates and derive a new accuracy metric in order to provide comparisons between the different learning strategies. The simulation results show the convergence of the learning model to a solution concept based on satisfaction equilibrium, under the uncertainty of the HN environment. We show that intra/inter-tier interference can be significantly reduced, thus resulting in higher cell throughputs.

Coordinated multi-point transmission for relaxation of self-backhauling bottlenecks in heterogeneous networks

The heterogeneous deployment of high-power macro cells and low-power nodes (LPNs) is now widely acknowledged as an essential requirement towards meeting the continued demand for mobile data capacity. The selection of the optimum backhaul solution for the LPNs obliges operators to consider not only the capacity of the backhaul but also other key factors so as to fully leverage the benefits provided by LPNs: the cost of the backhauling may limit the density of LPN deployments and the backhaul configuration requirements impact on the flexibility of LPN deployment. To that end, self-backhauling of LPNs via the existing macro radio access network (RAN) provides an attractive solution, particularly for deployment scenarios that are very cost-sensitive and/or require high flexibility. However, use of self-backhauling usually makes backhaul as a bottleneck due to the a) limited bandwidth allocated for legacy macro RAN, b) the need to share resources with macro user equipment (UE), and c) the high-intercell interference particularly in the macro cell edge. In this paper, we provide an overview of self-backhauled LPNs and investigate possible performance enhancements through the use of coordinated multi-point (CoMP) transmission to relax the downlink backhaul capacity bottleneck for self-backhauled LPNs. To that end, we carry out analytical studies for a practical limited-feedback CoMP technique and numerically verify the derived capacity outage expressions. Furthermore, we implement a simulation study for an exemplary heterogeneous network deployment in a realistic radio propagation environment. The results of the studies demonstrate that significant spectral efficiency and throughput gains for the LPN backhaul are achievable through the use of selected CoMP technique under realizable feedback overhead, even under feedback bit error. The achieved relaxation in the backhaul bottleneck is observed providing improved performance for the UEs served by the LPNs. Furthermore, more resources will be available for macro UEs leading to overall performance gains compared to the case without CoMP.

Scalable HetNet interference management and the impact of limited channel state information

Interference management is important in wireless cellular networks such as long-term evolution (LTE) and LTE-A, where orthogonal frequency division multiple access (OFDMA), dense frequency reuse and heterogeneous cell sizes and capabilities provide great performance at the cost of increased network complexity. The layered structures of emerging cellular networks and their dynamic environments limit greatly the efficacy of traditional static interference management methods. Furthermore, conventional interference coordination techniques assume that perfect channel knowledge is available and that the signalling overhead can be neglected. In this paper, we analyse a heterogeneous LTE OFDMA downlink network composed by macro-, pico- and femtocells. We propose a low-complexity, distributed and cooperative interference mitigation method which is aware of network load and propagation conditions. The proposed method is fully scalable and addresses the interference received by the macro and pico layer and the interference received by femtocells separately. The new solution makes use of the iterative Hungarian algorithm, which effectively reduces interference and enhances the quality of service of starved users when compared to other state-of-the-art solutions. The proposed method outperforms static solutions by providing comparable results for the cell edge users (the proposed solution delivers 86% of the gain of a static frequency reuse 3) while presenting no loss at the cell centre, compared to an 18% loss of the frequency reuse 3 in a homogeneous scenario. In a heterogeneous network (HetNet) deployment, it generates a gain of 45% for the combined macro and pico edge users at a very small cost for the cell centre lower than 4% when compared with standard resource allocation. It optimizes greatly picocell performance, with improvements of more than 50% at a small cost for femtocell users (15%). In order to apply the proposed method to a practical network, the impact of the necessary quantization of channel state information on the interference management solution is studied and results show that signalling overhead can be contained while performance is improved by increasing resolution on the portions of the bandwidth more likely to be assigned to the users.