Deployment Of Heterogeneous Networks Research Articles

Deployment analysis and optimization of heterogeneous networks under the spectrum underlay strategy

To meet the growing mobile traffic demand, deployment of heterogeneous networks (HetNets) is proposed as a solution to enhance network capacity. It will enable the coexistence of several systems consisting of Macro, Micro, and Femto or WiFi layers. However, the main issue is the coexistence due to mutual interference. To guarantee that HetNet performance will not be compromised due to the interference, some deployment parameters should be controlled, such as primary exclusion zones and density of users. In this context, the present work provides deployment analysis and optimization for a Macro-Femto scenario, considering interference constraints to maximize the data rate of the HetNet. To fulfill this, we characterize some spectrum underlay scenarios in which HetNets would be expected to operate, setting different signal-to-interference-plus-noise ratio (SINR) thresholds. They are evaluated using a solution procedure based on the socio-cognitive particle swarm optimization (SCPSO) algorithm. Considering the best scenarios found, we show deployment parameters to achieve maximum system throughput, such as density of femto-users and primary exclusion zones of macro-users.

Energy-Aware Cellular Deployment Strategy Under Coverage Performance Constraints

The last ten years have witnessed explosive growth in mobile data traffic, which leads to rapid increases in energy consumption of cellular networks. One potential solution to this issue is to seek out a green deployment strategy. In this paper, we investigate the energy-efficient deployment strategy under coverage performance constraints for both homogeneous and heterogeneous cellular networks. Unlike just considering the base station (BS) density in previous work, we jointly optimize the BS density and the BS transmission power. First, we derive the relation between the average coverage probability and deployment strategy (i.e., BS density and BS transmission power) with stochastic geometry tools. Then, based on the expression results, we formulate a network energy consumption minimization framework considering coverage performance constraints and jointly determine the optimal macro BS (MaBS) density, MaBS transmission power, and micro BS (MiBS) density. With practical data sets, numerical simulation results show the following: 1) compared with homogeneous network deployment, heterogeneous network deployment has the advantage in energy efficiency performance, and 2) our joint BS density and BS transmission power optimization strategy exceeds the existing strategy, which just considers the BS density optimization in terms of energy efficiency.

Wireless Femto-Relays

The continuous increase in mobile data traffic creates the need for radical innovations in the mobile broadband system design. Heterogeneous networks (HetNets) deployment paradigm is an emerging research trend considered as the most significant aspect for meeting the mobile data challenge, mainly by proposing spectral efficiency enhancements and cell capacity gains from an overall system perspective. Two are the main challenges that dense small cell networks are facing: a) various types of interference mainly caused by unplanned deployments, and b) limited and Quality of Service (QoS)-unreliable wired backhaul links. In this paper, the authors propose a model where femtocells' and relays' complementary characteristics are effectively exploited into femto-relays. More specifically, the authors describe four main functionalities of this model: a) interference protection, b) two-fold backhaul alternatives (i.e. wired and wireless backhaul), c) opportunistic femto-relay selection, and d) full-duplex in-band relaying. To evaluate the anticipated technical impact of the proposed model, targeted simulation results are presented for a campus topology where femto-relays are compared with classic femtocells. Finally, related open issues, such as signaling overheads management, context-aware resource management, and business logic aspects are presented, with emphasis on the femto-relay's real market penetration opportunities in the mid and long-term future.

Energy-Efficient Base Station Deployment in Heterogeneous Networks

In this letter, we address the base station (BS) deployment problem in heterogeneous networks (HetNets) and propose an energy-efficient solution. Supporting the network with additional BSs increases the total capacity of the network. However, this process may reduce the energy efficiency of the network. The proposed algorithm studies the energy efficiency aspect of the micro BS deployment problem. The deployment problem can be divided into two subproblems: choosing candidate locations for micro BSs and selecting the optimum set among these candidates. Inhomogeneous distribution of the candidate locations is misleading for different user sets. Selecting the optimum micro BSs among the candidate locations is a combinatorial problem. To provide an approximate solution to this problem, we propose a greedy algorithm. Our simulation results demonstrate that by optimizing the BS location and the number of BSs to be deployed, the energy efficiency of the system with only macro BSs can be improved up to 1.4-1.65 times for a range of realistic micro BS transmit power levels.

Learning Based Frequency- and Time-Domain Inter-Cell Interference Coordination in HetNets

In this article, we focus on inter-cell interference coordination (ICIC) techniques in heterogeneous network (Het-Net) deployments, whereby macro- and picocells autonomously optimize their downlink transmissions, with loose coordination. We model this strategic coexistence as a multi-agent system, aiming at joint interference management and cell association. Using tools from Reinforcement Learning (RL), agents (i.e., macro- and picocells) sense their environment, and self-adapt based on local information so as to maximize their network performance. Specifically, we explore both time- and frequency domain ICIC scenarios, and propose a two-level RL formulation. Here, picocells learn their optimal cell range expansion (CRE) bias and transmit power allocation, as well as appropriate frequency bands for multi-flow transmissions, in which a user equipment (UE) can be simultaneously served by two or more base stations (BSs) from macro- and pico-layers. To substantiate our theoretical findings, Long Term Evolution Advanced (LTEA) based system level simulations are carried out in which our proposed approaches are compared with a number of baseline approaches, such as resource partitioning (RP), static CRE, and single-flow Carrier Aggregation (CA). Our proposed solutions yield substantial gains up to 125% compared to static ICIC approaches in terms of average UE throughput in the timedomain. In the frequency-domain our proposed solutions yield gains up to 240% in terms of cell-edge UE throughput.

Seamless handover between unicast and multicast multimedia streams

With the deployment of heterogeneous networks, mobile users are expecting ubiquitous connectivity when using applications. For bandwidth-intensive applications such as Internet Protocol Television (IPTV), multimedia contents are typically transmitted using a multicast delivery method due to its bandwidth efficiency. However, not all networks support multicasting. Multicasting alone could lead to service disruption when the users move from a multicast-capable network to a non-multicast network. In this paper, we propose a handover scheme called application layer seamless switching (ALSS) to provide smooth real-time multimedia delivery across unicast and multicast networks. ALSS adopts a soft handover to achieve seamless playback during the handover period. A real-time streaming testbed is implemented to investigate the overall handover performance, especially the overlapping period where both network interfaces are receiving audio and video packets. Both the quality of service (QoS) and objective-mapped quality of experience (QoE) metrics are measured. Experimental results show that the overlapping period takes a minimum of 56 and 4 ms for multicast-to-unicast (M2U) and unicast-to-multicast (U2M) handover, respectively. The measured peak signal-to-noise ratio (PSNR) confirms that the frame-by-frame quality of the streamed video during the handover is at least 33 dB, which is categorized as good based on ITU-T recommendations. The estimated mean opinion score (MOS) in terms of video playback smoothness is also at a satisfactory level.

Energy-Efficient Design in Heterogeneous Cellular Networks Based on Large-Scale User Behavior Constraints

Large-scale user behavior can be used as the guidance for deployment, configuration, and service control in heterogeneous cellular networks (HCNs). However, in wireless networks, large-scale user behavior (in terms of traffic fluctuation in spatial domain) follows inhomogeneous distribution, which brings enormous challenges to energy-efficient design of HCNs. In this paper, the heterogeneity of large-scale user behavior is quantitatively characterized and exploited to study the energy efficiency (EE) in HCNs. An optimization problem is formulated for energy-efficient two-tier deployment and configuration, where the base station (BS) density, BS transmit power, BS static power, and quality of service are taken into account. We present closed-form formulas that establish the quantitative relationship between large-scale user behavior and energy-efficient HCN configuration. These results can be used to determine BS density and BS transmit power with the objective of achieving optimal EE. Furthermore, we present three energy-efficient control strategies of micro BSs, including micro BS sleep control, coverage expansion control, and coverage shrinking control. Simulation results validate our theoretical analysis and demonstrate that the proposed control strategies can potentially lead to significant power savings.

Introduction to Special Issue “Intelligent Telecommunication Infrastructures and Beyond”

The development of services and applications require increasingly levels of performance, quality of service and sophistication from the telecommunication infrastructures. New types of communications, technologies and services indicate that there will be a need for significant innovation in the telecommunication infrastructures of today. There are signs that a critical level of usage and complexity has been already reached which is putting pressure for changes on the existing infrastructures. We witness the development and proposals for new intelligent network solutions, next generation access and overlay networks, virtual infrastructures, cloud technologies, network convergence, etc. All this was a motivation to try to raise a discussion among the research community to highlight the state of the art and future tendencies in the development of intelligent and next generation telecommunication systems and infrastructures. This special issue ismainly composedof the extendedversions of selectedpapers presented at the 1st Center of TeleInFrastructure—South-East Europe (CTIF SEE) Workshop I2B: “Intelligent Infrastructures and Beyond”, 16 September 2013, Sofia, Bulgaria (www.ctif. aau.dk). Nevertheless in the issue are also included selected papers from academia, research and industry contributing advances and ideas on this topic. Several papers in this special issue are related to future heterogeneous cellular network deployments and software defined networks where topics such as resource management, design scenarios and deployment solutions are considered. An approach for resource management for Heterogeneous Networks (HetNets) based on dynamic user association and a characteristic model of the servicing properties of a HetNet access point is proposed in the

Power–Throughput Tradeoff in MIMO Heterogeneous Networks

We consider a single-macrocell heterogeneous multiple-input multiple-output network, where the macrocell shares the same frequency band with the femto network. The interference power to the macro users from the femto base stations is kept below a threshold to guarantee that the performance of the macro users does not degrade due to the femto network. We consider the problem of finding the set of all achievable power-rate tuples for this setting. We first formulate a two-dimensional vector optimization problem in which we consider maximizing the sum-rate and minimizing the sum-power, subject to maximum power and interference threshold constraints. The considered problem is NP-hard. We provide a method to solve the problem by using the relationship between the weighted sum-rate maximization and weighted-sum-mean-squared-error minimization problems. Furthermore, using the proposed algorithm, we evaluate the impact of imposing interference threshold constraints and the impact of co-channel deployment in heterogeneous networks. The proposed algorithm can be used to evaluate the performance of real heterogeneous networks via off-line numerical simulations.

Expanding cellular coverage via cell-edge deployment in heterogeneous networks: spectral efficiency and backhaul power consumption perspectives

Heterogeneous small-cell networks (HetNets) are considered to be a standard part of future mobile networks where operator/consumer deployed small-cells, such as femtocells, relays, and distributed antennas (DAs), complement the existing macrocell infrastructure. This article proposes the need-oriented deployment of smallcells and device-to-device (D2D) communication around the edge of the macrocell such that the small-cell base stations (SBSs) and D2D communication serve the cell-edge mobile users, thereby expanding the network coverage and capacity. In this context, we present competitive network configurations, namely, femto-on-edge, DA-onedge, relay-on-edge, and D2D-communication on- edge, where femto base stations, DA elements, relay base stations, and D2D communication, respectively, are deployed around the edge of the macrocell. The proposed deployments ensure performance gains in the network in terms of spectral efficiency and power consumption by facilitating the cell-edge mobile users with small-cells and D2D communication. In order to calibrate the impact of power consumption on system performance and network topology, this article discusses the detailed breakdown of the end-to-end power consumption, which includes backhaul, access, and aggregation network power consumptions. Several comparative simulation results quantify the improvements in spectral efficiency and power consumption of the D2D-communication-onedge configuration to establish a greener network over the other competitive configurations.

Device-to-device communications in cellular networks

Device-to-device communications enable two proximity users to transmit signal directly without going through the base station. It can increase network spectral efficiency and energy efficiency, reduce transmission delay, offload traffic for the BS, and alleviate congestion in the cellular core networks. However, many technical challenges need to be addressed for D2D communications to harvest the potential benefits, including device discovery and D2D session setup, D2D resource allocation to guarantee QoS, D2D MIMO transmission, as well as D2D-aided BS deployment in heterogeneous networks. In this article, the basic concepts of D2D communications are first introduced, and then existing fundamental works on D2D communications are discussed. In addition, some potential research topics and challenges are also identified.

Beamforming for small cell deployment in LTE-advanced and beyond

Integrating the standard coverage of traditional macrocells with cells of reduced dimensions (i.e., small cells) is considered one of the main enhancements for Long Term Evolution systems. Small cells will be overlapped with macrocells and possibly also with each other in areas where wider coverage capability and higher throughput are needed. Such heterogeneous network deployment presents many potential benefits but also some challenges that need to be resolved. In particular, multi-antenna techniques and processing in the spatial domain will be key enabling factors to mitigate these issues. This article presents different small cell deployment approaches: sharing the same frequency bands with the macrocell, or using separated higher frequency bands. For each approach, the benefits of beamforming are discussed.

Energy-Efficient Planning Tool for WCDMA Heterogeneous Network Deployment

The population of powerful mobile network technologies has increased in recent years also focus has been shifting from second generation mobile to third generation technology. This higher access rates have led to increased energy consumption in base stations (BTS) and network densities have been constantly growing. This paper developed an energy efficient planning tool for analytical modeling of heterogeneous networks and observed the potential energy savings statistics when deploying heterogeneous networks. A model developed from wcdma downlink equation was used in determining the energy consumption per unit area of the network. The model was also used to observe how heterogeneous network deployment contributes to the total energy consumption of the network. The result was presented in three scenarios. The first scenario presented the daily energy consumption per square kilometer and it was observed that the energy consumption by the macrocell decreases when increasing the ratio of femtocells in the network. However, the introduction of femtocells to the network ordinarily does not gauranty decrease in energy consumption the scenario depends on the power budget of the femtocells as presented in second and third scenarios where power budget of 2 W and 5 W were used respectively. By introducing femtocell of low power budget into the network, the density of the network reduces therefore, bringing about reasonable reduction in the total power consumption of the network. To that end, this research developed software that helps to observe the total energy that could be saved when deploying heterogeneous networks.

A multi-point transmission scheme for cross-tier interference mitigation in downlink heterogeneous networks

Heterogeneous network (HetNet) deployment comprising of high power macro nodes overlaid with pico nodes and various other types of low power nodes has been considered as one of the key enabling technology in 3GPP LTE-Advanced. HetNet can significantly enhance the capacity and coverage of cellular networks. However, severe inter-cell interference (ICI) between high power macro and low power pico nodes is a critical performance limiting factor for cell-edge users in HetNet. Coordinated multipoint transmission (CoMP) has been recognized as an effective technique to mitigate ICI in LTE-A. However, backhaul overhead and complexity are critical issues in CoMP. In this paper we propose a novel scheme that utilizes the benefits of HetNet to improve the system capacity and coverage. Moreover it exploits coordinated multi-point transmission to effectively mitigate ICI with reduced feedback overhead and complexity. In our scheme the users with high signal to interference plus noise ratio are served by the respective macro and pico cells. However, for users in high interference region, coordinated multi-point joint transmission is adopted to increase the radio signal strength and effectively mitigate ICI. The proposed scheme outperforms the conventional system with reduced backhaul overhead and complexity. System level simulations illustrate that the proposed scheme attains higher performance as compared to conventional schemes.

Energy Efficient Deployment of Heterogeneous Networks

A novel energy efficient heterogeneous networks (HetNet) deployment scheme is proposed in this paper. Unlike the traditional deployment, we consider the scenario with picocell eNodeB (PeNB) at the edge instead of under the umbrella of macrocells in HetNet. In the novel scheme, one PeNB with directional antennas is deployed on the border of neighbor macrocells which is equivalent to a combiner of PeNBs to associate MeNBs around. Compared with the traditional scheme, we have proved that the novel scheme performs better in fairness and efficiency, in terms of coverage area (proportional to offload rate), spectrum and energy efficiency for both edge users and overall users. Meanwhile, the technologies that try to reduce the difference and imbalance of the transmit power in HetNet obtain more inherent gains in the novel scheme, such as cell range expanded (CRE). Our results show that, the scheme proposed is also a spectrum and energy efficient heterogeneous deployment scheme that the energy efficiency is increased from 20% up to nearly 60%

Proposal of a Hierarchical and Distributed Method for Selecting a Radio Network and a Transmission Mode

The deployment of heterogeneous radio networks and the deployment of Unicast Internet Protocol (IP)/Multicast IP architectures can impact the quality of services received by the users. The authors think that they will accept these quality variations if they have the possibility to choose the radio network and the transmission mode, multicast versus unicast. But, when choosing a radio network or a transmission mode, the choices of the users can be opposed to the choices of the operators managing the networks. To overcome this drawback, the authors defined a method allowing the users, the operators managing the networks and the service providers to cooperate in the selection process.

Design of Cost-Optimal Passive Optical Networks for Small Cell Backhaul Using Installed Fibers [Invited

With the recent popularity of mobile data devices, the demand for mobile data traffic has grown rapidly as never before. Hence, service providers are trying to come up with cost-effective solutions to battle this ever increasing demand for bandwidth in their cellular networks. Deployment of a denser heterogeneous network, with a large number of small cells, has been identified as an effective strategy not only to satisfy this unabated growth in mobile data traffic but also to facilitate ubiquitous wireless access. While the cost associated with on-site small cell equipment is low in comparison with a typical macro cell, deployment of small cells opens a new set of challenges, especially in relation to expenditures and capacity requirements associated with the backhaul. In this paper we discuss an efficient small cell backhauling strategy that leverages existing fiber resources in a cost-optimal manner. In particular, we formulate an optimization framework for planning a cost-minimized backhaul for a small cell network, which is based on the deployment of passive optical networks on top of the existing infrastructure. We demonstrate the effectiveness of our method by using our optimization framework to design a cost-optimal backhaul for a small portion of a realistic backhaul network. Our results show that in comparison to the typical point-to-point fiber backhauling approach, our technique can halve the costs associated with small cell backhaul deployment.

Particle swarm optimization based network selection in heterogeneous wireless environment

Deployment of heterogeneous wireless networks is spreading throughout the world as users want to be connected anytime, anywhere, and anyhow. Meanwhile, users are increasingly interested in multimedia applications such as audio, video streaming and Voice over IP (VoIP), which require strict Quality of Service (QoS) support. Provisioning of Always Best Connected (ABC) network with such constraints is a challenging task. Considering the availability of various access technologies, it is difficult for a network operator to find reliable criteria to select the best network that ensures user satisfaction while reducing multiple network selection. Designing an efficient Network selection algorithm, in this type of environment, is an important research problem. In this paper, we propose a novel network selection algorithm utilizing signal strength, available bit rate, signal to noise ratio, achievable throughput, bit error rate and outage probability metrics as criteria for network selection. The selection metrics are combined with PSO for relative dynamic weight optimization. The proposed algorithm is implemented in a typical heterogeneous environment of EDGE (2.5G) and UMTS (3G). Switching rate of the user between available networks has been used as the performance metric. Moreover, a utility function is used to maintain desired QoS during transition between networks, which is measured in terms of the throughput. It is shown here that PSO based approach yields optimal network selection in heterogeneous wireless environment.

5G on the Horizon: Key Challenges for the Radio-Access Network

Toward the fifth generation (5G) of wireless/mobile broadband, numerous devices and networks will be interconnected and traffic demand will constantly rise. Heterogeneity will also be a feature that is expected to characterize the emerging wireless world, as mixed usage of cells of diverse sizes and access points with different characteristics and technologies in an operating environment are necessary. Wireless networks pose specific requirements that need to be fulfilled. In this respect, approaches for introducing intelligence will be investigated by the research community. Intelligence shall provide energy- and cost-efficient solutions at which a certain application/service/quality provision is achieved. Particularly, the introduction of intelligence in heterogeneous network deployments and the cloud radio-access network (RAN) is investigated. Finally, elaboration on emerging enabling technologies for applying intelligence will focus on the recent concepts of software-defined networking (SDN) and network function virtualization (NFV). This article provided an overview for delivering intelligence toward the 5G of wireless/mobile broadband by taking into account the complex context of operation and essential requirements such as QoE, energy efficiency, cost efficiency, and resource efficiency.

A holistic view on hyper-dense heterogeneous and small cell networks

The wireless industry has been experiencing an explosion of data traffic usage in recent years and is now facing an even bigger challenge, an astounding 1000-fold data traffic increase in a decade. The required traffic increase is in bits per second per square kilometer, which is equivalent to bits per second per Hertz per cell × Hertz × cell per square kilometer. The innovations through higher utilization of the spectrum (bits per second per Hertz per cell) and utilization of more bandwidth (Hertz) are quite limited: spectral efficiency of a point-to-point link is very close to the theoretical limits, and utilization of more bandwidth is a very costly solution in general. Hyper-dense deployment of heterogeneous and small cell networks (HetSNets) that increase cells per square kilometer by deploying more cells in a given area is a very promising technique as it would provide a huge capacity gain by bringing small base stations closer to mobile devices. This article presents a holistic view on hyperdense HetSNets, which include fundamental preference in future wireless systems, and technical challenges and recent technological breakthroughs made in such networks. Advancements in modeling and analysis tools for hyper-dense HetSNets are also introduced with some additional interference mitigation and higher spectrum utilization techniques. This article ends with a promising view on the hyper-dense HetSNets to meet the upcoming 1000× data challenge.