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Showing papers in "IEEE Wireless Communications in 2015"


Journal ArticleDOI
TL;DR: This article comprehensively surveys recent advances in fronthaul-constrained CRANs, including system architectures and key techniques, including compression and quantization, large-scale coordinated processing and clustering, and resource allocation optimization.
Abstract: As a promising paradigm for fifth generation wireless communication systems, cloud radio access networks (C-RANs) have been shown to reduce both capital and operating expenditures, as well as to provide high spectral efficiency (SE) and energy efficiency (EE). The fronthaul in such networks, defined as the transmission link between the baseband unit and the remote radio head, requires a high capacity, but is often constrained. This article comprehensively surveys recent advances in fronthaul-constrained CRANs, including system architectures and key techniques. Particularly, major issues relating to the impact of the constrained fronthaul on SE/EE and quality of service for users, including compression and quantization, large-scale coordinated processing and clustering, and resource allocation optimization, are discussed together with corresponding potential solutions. Open issues in terms of software-defined networking, network function virtualization, and partial centralization are also identified.

436 citations


Journal ArticleDOI
TL;DR: The feasibility of mmWave massive-MIMO-based wireless backhaul for 5G UDN is discussed, and the benefits and challenges are addressed, and a digitally controlled phase shifter network (DPSN)-based hybrid precoding/combining scheme for mmWavemassive MIMO is proposed.
Abstract: The ultra-dense network (UDN) has been considered as a promising candidate for future 5G networks to meet the explosive data demand. To realize UDN, a reliable, gigahertz bandwidth, and cost-effective backhaul connecting ultradense small-cell BSs and macrocell BS are prerequisite. Millimeter-wave can provide the potential gigabit-per-second traffic for wireless backhaul. Moreover, mmWave can easily be integrated with massive MIMO for improved link reliability. In this article, we discuss the feasibility of mmWave massive-MIMO-based wireless backhaul for 5G UDN, and the benefits and challenges are also addressed. In particular, we propose a digitally controlled phase shifter network (DPSN)-based hybrid precoding/combining scheme for mmWave massive MIMO, whereby the low-rank property of the mmWave massive MIMO channel matrix is leveraged to reduce the required cost and complexity of a transceiver with a negligible performance loss. One key feature of the proposed scheme is that the macrocell BS can simultaneously support multiple small-cell BSs with multiple streams for each small-cell BS, which is essentially different from conventional hybrid precoding/combining schemes, typically limited to single-user MIMO with multiple streams or multi-user MIMO with single stream for each user. Based on the proposed scheme, we further explore the fundamental issues of developing mmWave massive MIMO for wireless backhaul, and the associated challenges, insight, and prospects to enable mmWave massive-MIMO-based wireless backhaul for 5G UDN are discussed.

418 citations


Journal ArticleDOI
TL;DR: Simulation results demonstrate that LTE-U can provide better user experience to LTE users while well protecting the incumbent WiFi users' performance compared to two existing advanced technologies: cellular/WiFi interworking and licensed-only heterogeneous networks (Het-Nets).
Abstract: The phenomenal growth of mobile data demand has brought about increasing scarcity in available radio spectrum. Meanwhile, mobile customers pay more attention to their own experience, especially in communication reliability and service continuity on the move. To address these issues, LTE-Unlicensed, or LTEU, is considered one of the latest groundbreaking innovations to provide high performance and seamless user experience under a unified radio technology by extending LTE to the readily available unlicensed spectrum. In this article, we offer a comprehensive overview of the LTEU technology from both operator and user perspectives, and examine its impact on the incumbent unlicensed systems. Specifically, we first introduce the implementation regulations, principles, and typical deployment scenarios of LTE-U. Potential benefits for both operators and users are then discussed. We further identify three key challenges in bringing LTE-U into reality together with related research directions. In particular, the most critical issue of LTE-U is coexistence with other unlicensed systems, such as widely deployed WiFi. The LTE/WiFi coexistence mechanisms are elaborated in time, frequency, and power aspects, respectively. Simulation results demonstrate that LTE-U can provide better user experience to LTE users while well protecting the incumbent WiFi users’ performance compared to two existing advanced technologies: cellular/WiFi interworking and licensed-only heterogeneous networks (Het-Nets).

370 citations


Journal ArticleDOI
TL;DR: This article presents and discusses some of the integration challenges that must be addressed to enable an intelligent transportation system to address issues facing the transportation sector such as high fuel prices, high levels of CO2 emissions, increasing traffic congestion, and improved road safety.
Abstract: Transportation is a necessary infrastructure for our modern society. The performance of transportation systems is of crucial importance for individual mobility, commerce, and for the economic growth of all nations. In recent years modern society has been facing more traffic jams, higher fuel prices, and an increase in CO2 emissions. It is imperative to improve the safety and efficiency of transportation. Developing a sustainable intelligent transportation system requires the seamless integration and interoperability with emerging technologies such as connected vehicles, cloud computing, and the Internet of Things. In this article we present and discuss some of the integration challenges that must be addressed to enable an intelligent transportation system to address issues facing the transportation sector such as high fuel prices, high levels of CO2 emissions, increasing traffic congestion, and improved road safety.

357 citations


Journal ArticleDOI
TL;DR: Various transportation services provided by VANET-Cloud are reviewed, and some future research directions are highlighted, including security and privacy, data aggregation, energy efficiency, interoperability, and resource management.
Abstract: Cloud computing is a network access model that aims to transparently and ubiquitously share a large number of computing resources. These are leased by a service provider to digital customers, usually through the Internet. Due to the increasing number of traffic accidents and dissatisfaction of road users in vehicular networks, the major focus of current solutions provided by intelligent transportation systems is on improving road safety and ensuring passenger comfort. Cloud computing technologies have the potential to improve road safety and traveling experience in ITSs by providing flexible solutions (i.e., alternative routes, synchronization of traffic lights, etc.) needed by various road safety actors such as police, and disaster and emergency services. In order to improve traffic safety and provide computational services to road users, a new cloud computing model called VANET-Cloud applied to vehicular ad hoc networks is proposed. Various transportation services provided by VANET-Cloud are reviewed, and some future research directions are highlighted, including security and privacy, data aggregation, energy efficiency, interoperability, and resource management.

292 citations


Journal ArticleDOI
TL;DR: This article describes the cellular region in which the downlink transmission capacity for a user served by a given half-duplex small cell becomes limited by the backhaul link capacity, and illustrates solution techniques to improve the performance of wireless backhauling for small cells.
Abstract: Dense deployment of small cells over traditional macrocells is considered as a key enabling technique for the emerging 5G cellular networks. However, a fundamental challenge is to provide an economical and ubiquitous backhaul connectivity to these small cells. There is a wide range of backhaul solutions that together can address the backhaul challenges of 5G networks. In this context, this article provides an overview of the different backhaul solutions and highlights the perceived challenges in backhauling small cells. A qualitative overview of the existing research studies and their critical assumptions are then discussed. Next, for backhauling downlink traffic of a small cell user, we characterize the cellular region in which the downlink transmission capacity for a user served by a given half-duplex small cell becomes limited by the backhaul link capacity. We then illustrate solution techniques such as full-duplex backhauling to improve the performance of wireless backhauling for small cells.

280 citations


Journal ArticleDOI
TL;DR: This article investigates how the hybrid array architecture and special mm-Wave channel property can be exploited to design suboptimal but practical massive antenna array schemes and compares two main types of hybrid arrays, interleaved and localized arrays, and recommends that the localized array is a better option in terms of overall performance and hardware feasibility.
Abstract: A massive hybrid array consists of multiple analog subarrays, with each subarray having its digital processing chain. It offers the potential advantage of balancing cost and performance for massive arrays and therefore serves as an attractive solution for future millimeter-wave (mm- Wave) cellular communications. On one hand, using beamforming analog subarrays such as phased arrays, the hybrid configuration can effectively collect or distribute signal energy in sparse mm-Wave channels. On the other hand, multiple digital chains in the configuration provide multiplexing capability and more beamforming flexibility to the system. In this article, we discuss several important issues and the state-of-the-art development for mm-Wave hybrid arrays, such as channel modeling, capacity characterization, applications of various smart antenna techniques for single-user and multiuser communications, and practical hardware design. We investigate how the hybrid array architecture and special mm-Wave channel property can be exploited to design suboptimal but practical massive antenna array schemes. We also compare two main types of hybrid arrays, interleaved and localized arrays, and recommend that the localized array is a better option in terms of overall performance and hardware feasibility.

245 citations


Journal ArticleDOI
TL;DR: Numerical results show that with the proposed network architecture, CoMP clustering and handover management schemes can significantly increase the capacity of HCSNet while maintaining users' quality of service.
Abstract: Heterogeneous small cell networks have attracted much attention for satisfying users’ explosive data traffic requirements. The heterogeneous cloud small cell network (HCSNet), which combines cloud computing and a heterogeneous small cell network, will likely play an important role in 5G mobile communication networks. However, with massive deployment of small cells, co-channel interference and handover management are two important problems in an HCSNet, especially for cell edge users. In this article, we examine the problems of cooperative interference mitigation and handover management in an HCSNet. A network architecture is described to combine cloud radio access network with small cells. An effective CoMP clustering scheme using affinity propagation is adopted to mitigate cell edge users’ interference. A low-complexity handover management scheme is presented, and its signaling procedure is analyzed in an HCSNet. Numerical results show that with the proposed network architecture, CoMP clustering and handover management schemes can significantly increase the capacity of HCSNet while maintaining users’ quality of service.

208 citations


Journal ArticleDOI
TL;DR: A novel simultaneous wireless information and power transfer scheme based on OC in IA wireless networks is proposed and the methods to reduce the complexity of the OC-based IA algorithms are summarized.
Abstract: IA is a promising technology for interference management in wireless networks. However, there are still some practical challenges. Signal to interference plus noise ratio (SINR) decrease is one of the key challenging issues due to the inherent property of IA and channel fading. Recent advances in OC, including multiuser diversity and antenna selection, can be applied in IA wireless networks to improve the SINR performance. In this article we review some existing research work on OC-based IA wireless networks. In addition, we propose a novel simultaneous wireless information and power transfer scheme based on OC in IA wireless networks. Simulation results are presented to show the performance comparison of these schemes. The methods to reduce the complexity of the OC-based IA algorithms are finally summarized.

183 citations


Journal ArticleDOI
TL;DR: A novel concept of wireless charger networking is proposed that allows chargers to be connected to facilitate information collection and control and shows the benefit in terms of reduced costs for users to identify the best charger to replenish energy for their mobile devices.
Abstract: Wireless charging is a technique of transmitting power through an air gap to an electrical device for the purpose of energy replenishment. Recently, wireless charging technology has significantly advanced in terms of efficiency and functionality. This article first presents an overview and fundamentals of wireless charging. We then provide the review of standards, that is, Qi and the Alliance for Wireless Power, and highlight their communication protocols. Next, we propose a novel concept of wireless charger networking that allows chargers to be connected to facilitate information collection and control. We demonstrate the application of the wireless charger network in user-charger assignment, which clearly shows the benefit in terms of reduced costs for users to identify the best chargers to replenish energy for their mobile devices.

176 citations


Journal ArticleDOI
TL;DR: The context of VLC is outlined, its unique benefits are outlined, and the state of the art research contributions of the assembled papers are described.
Abstract: Visible light communications (VLC) is an emerging field of optical communications that focuses on the part of the electromagnetic spectrum that humans can see. Much existing work in optical communications exists, mainly optimized for capacity and transmission performance in fiber and free-space with biases toward spectrum that minimizes attenuation in the medium. However, the use of the visible spectrum has gained interest due to its availability and the ease at which it can be modulated using light emitting diodes (LEDs). Recent demand factors due to the burgeoning mobile industry and the rapid evolution of LED-based lighting are also driving this interest. Here, and in this special issue, we outline the context of VLC, its unique benefits, and describe the state of the art research contributions of the assembled papers.

Journal ArticleDOI
TL;DR: A novel architecture, Affective Interaction through Wearable Computing and Cloud Technology (AIWAC), which includes three components: collaborative data collection via wearable devices, enhanced sentiment analysis and forecasting models, and controllable affective interactions is proposed.
Abstract: To reduce the heavy burden from rapidly growing demands of healthcare service, wearable computing-assisted healthcare has been proposed for health monitoring and remote medical care. Although the provisioning of healthcare services can be significantly enhanced via wearableenabled technologies, great challenges arise due to the lack of a human-centric mechanism for affective interaction. In this article, we propose a novel architecture, Affective Interaction through Wearable Computing and Cloud Technology (AIWAC), which includes three components: collaborative data collection via wearable devices, enhanced sentiment analysis and forecasting models, and controllable affective interactions. Based on the proposed architecture, we present our AIWAC testbed, design a practical mechanism for wearable computing-based emotional interaction, and discuss its open problems, which inspire potential research as a new direction.

Journal ArticleDOI
TL;DR: A brief survey on some of the work that has been done on wireless virtualization in cellular networks is provided and a framework that enables wirelessvirtualization is presented that is based on the motivations and business models.
Abstract: With wireless virtualization, the overall expenses of mobile cellular network deployment and operation can be significantly reduced by abstracting and sharing infrastructure and radio spectrum resources. Moreover, wireless virtualization can provide easier migration to newer products or technologies by isolating part of the network. Despite the potential vision of wireless virtualization, several significant research challenges remain. In this article, we provide a brief survey on some of the work that has been done on wireless virtualization in cellular networks. We also present the motivations and business models of wireless virtualization. Furthermore, we present a framework that enables wireless virtualization. In addition, we discuss a number of challenges that need to be addressed for the deployment of wireless virtualization in next generation mobile cellular networks.

Journal ArticleDOI
TL;DR: The Xhaul architecture is presented, aimed at developing a 5G integrated backhaul and fronthaul transport network enabling flexible and software-defined reconfiguration of all networking elements in a multi-tenant and service-oriented unified management environment.
Abstract: The Xhaul architecture presented in this article is aimed at developing a 5G integrated backhaul and fronthaul transport network enabling flexible and software-defined reconfiguration of all networking elements in a multi-tenant and service-oriented unified management environment. The Xhaul transport network vision consists of high-capacity switches and heterogeneous transmission links (e.g., fiber or wireless optics, high-capacity copper, mmWave) interconnecting remote radio heads, 5G points of attachment (5GPoAs, e.g., macro- and small cells), centralized- processing units (mini data centers), and points of presence of the core networks of one or multiple service provider(s). This transport network shall flexibly interconnect distributed 5G radio access and core network functions, hosted on network centralized nodes, through the implementation of a control infrastructure using a unified, abstract network model for control plane integration (Xhaul Control Infrastructure, XCI); and a unified data plane encompassing innovative high-capacity transmission technologies and novel deterministic-latency switch architectures (Xhaul packet Forwarding Element, XFE). Standardization is expected to play a major role in a future 5G integrated front haul/backhaul architecture for multi-vendor interoperability reasons. To this end, we review the major relevant activities in the current standardization landscape and the potential impact on the Xhaul architecture.

Journal ArticleDOI
TL;DR: A cooperative D1D communication framework is proposed, which introduces the cooperative relay technique to conventional underlay/overlay D2D communications and extensive numerical results show the effectiveness of the proposed framework for a variety of scenarios.
Abstract: To meet the increasing demand of wireless broadband applications in 4G/beyond 4G cellular networks, D2D communication can serve as a candidate paradigm to improve spectrum efficiency. By reusing the spectrum of cellular users, two D2D users can form a direct data link without routing base stations and core networks; thus, the spectral efficiency can be improved. Further, when the cooperation between cellular users and D2D users is enabled, a win-win situation can be achieved to make all users better off. Thus motivated, we propose a cooperative D2D communication framework in this article, which introduces the cooperative relay technique to conventional underlay/overlay D2D communications. Adaptive mode selection and spectrum allocation schemes are also presented to ensure better performance for both cellular and D2D users. Extensive numerical results show the effectiveness of the proposed framework for a variety of scenarios.

Journal ArticleDOI
TL;DR: A fine-grained data search scheme is developed and its implementation on encrypted mobile cloud data, which is an effective balance between QoE and QoP in mobile cloudData outsourcing, is discussed.
Abstract: Mobile cloud computing can effectively address the resource limitations of mobile devices, and is therefore essential to enable extensive resource consuming mobile computing and communication applications. Of all the mobile cloud computing applications, data outsourcing, such as iCloud, is fundamental, which outsources a mobile user’s data to external cloud servers and accordingly provides a scalable and “always on” approach for public data access. With the security and privacy issues related to outsourced data becoming a rising concern, encryption on outsourced data is often necessary. Although encryption increases the quality of protection (QoP) of data outsourcing, it significantly reduces data usability and thus harms the mobile user’s quality of experience (QoE). How to strike a balance between QoP and QoE is therefore an important yet challenging task. In this article we focus on the fundamental problem of QoP and QoE provisioning in searchable encryption of data outsourcing. We develop a fine-grained data search scheme and discuss its implementation on encrypted mobile cloud data, which is an effective balance between QoE and QoP in mobile cloud data outsourcing.

Journal ArticleDOI
TL;DR: An overview of techniques related to modeling and distortion mitigation techniques of the nonlinearity in VLC systems is provided.
Abstract: Many physical devices used in VLC systems exhibit nonlinear effects, which can significantly degrade the overall system performance. For example, the LED is the major source of nonlinearity. The forward current is zero unless the forward voltage exceeds a turn-on value. The forward current is also limited with a maximum permissible value. In addition, the electrical-tooptical conversion is also nonlinear. In this article, we provide an overview of techniques related to modeling and distortion mitigation techniques of the nonlinearity in VLC systems. Appropriate models and robust nonlinearity mitigation techniques are crucial to support high-speed transmissions in practical VLC systems.

Journal ArticleDOI
TL;DR: This work introduces the user-centric design of VLC for heterogeneous networks (HetNet), where three key aspects are identified and elaborated on: signal coverage quality, system control, and service provision aspects.
Abstract: At the time of this writing, there is substantial research interest in the subject of visible light communications (VLC) owing to its ability to offer significant traffic offloading potential in highly crowded radio frequency (RF) scenarios. We introduce the user-centric design of VLC for heterogeneous networks (HetNet), where three key aspects are identified and elaborated on: signal coverage quality, system control, and service provision aspects. More explicitly, the concepts of amorphous cell formation as well as separated up-link (UL) and down-link (DL), decoupled data and control, dynamic load balancing (LB), etc., all demand radically new thinking. The advocated user-centric VLC design is of key significance in the small-cell scenarios of the emerging 5G design philosophy.

Journal ArticleDOI
TL;DR: Based on the existing RRM solutions and their limitations in multi-tier 5G systems with heterogeneous backhaul network architecture, backhaul- aware RRM strategies are envisioned and a case study of joint cell association and bandwidth allocation with a massive MIMO-based in-band wireless backhauling framework is presented.
Abstract: Developing efficient backhauling solutions for small cells is considered as one of the most significant challenges in the rollout of the upcoming 5G cellular systems where massive numbers of small cells will be deployed. In this article, we first review small cell evolutions and the consequent radio access network architecture evolution toward heterogeneity and centralized baseband processing. The backhaul solution, which is mainly determined by the availability of existing backhaul infrastructures and service demand, will lead to a heterogeneous backhaul network architecture. Radio resource management issues including cell association, and interference management and scheduling with inter-node coordination, as well as how they are related to backhaul solutions are discussed. Based on the existing RRM solutions and their limitations in multi-tier 5G systems with heterogeneous backhaul network architecture, backhaul- aware RRM strategies are envisioned. Results from a simple case study of joint cell association and bandwidth allocation with a massive MIMO-based in-band wireless backhauling framework are presented to demonstrate the performance gain with backhaul-aware RRM in a multi-tier cellular RAN. Several related open research issues are highlighted, and possible solution approaches are briefly discussed.

Journal ArticleDOI
TL;DR: In this issue, the general area of millimeter-wave mobile communications is revisiting because of more recent developments and the three basic developments include two major national regulatory agencies asking for and receiving comments on the approaches to be used.
Abstract: A few issues ago we wrote about issues of possible millimeter- wave use in 5G mobile communications systems [1]. In this issue we are revisiting the general area because of more recent developments. The three basic developments include two major national regulatory agencies asking for and receiving comments on the approaches to be used for millimeter-wave mobile communications and Working Party 5D of the International Telecommunication Union Radiocommunication Sector (ITU-R) updating its plans and schedules for 5G development and finalizing its view of a timeline toward what is now called "IMT-2020" or "IMT for 2020 and beyond."

Journal ArticleDOI
TL;DR: This article introduces the architecture of MHN, and point out the security and privacy challenges from the perspective of QoP, and presents some countermeasures for security and Privacy protection in MHNs, including privacy- preserving health data aggregation, secure health data processing, and misbehavior detection.
Abstract: With the flourishing of multi-functional wearable devices and the widespread use of smartphones, MHN becomes a promising paradigm of ubiquitous healthcare to continuously monitor our health conditions, remotely diagnose phenomena, and share health information in real time. However, MHNs raise critical security and privacy issues, since highly sensitive health information is collected, and users have diverse security and privacy requirements about such information. In this article, we investigate security and privacy protection in MHNs from the perspective of QoP, which offers users adjustable security protections at fine-grained levels. Specifically, we first introduce the architecture of MHN, and point out the security and privacy challenges from the perspective of QoP. We then present some countermeasures for security and privacy protection in MHNs, including privacy- preserving health data aggregation, secure health data processing, and misbehavior detection. Finally, we discuss some open problems and pose future research directions in MHNs.

Journal ArticleDOI
TL;DR: An overview on research in energy-efficient wireless networks during the past decade is provided and its potential applications toward the fifth generation cellular systems are discussed.
Abstract: This article provides an overview on research in energy-efficient wireless networks during the past decade and discusses its potential applications toward the fifth generation cellular systems. After analyzing the trade-off between spectrum efficiency and energy efficiency, various research results are summarized within a framework of energy-efficient resource allocation with optimization as a common tool. Then potential energy efficiency improving approaches in both physical layer and deployment aspects are provided. Finally, energy efficiency related open problems in massive multiple-input multiple- output, device-to-device communications, ultra dense networks, and other emerging technologies are identified.

Journal ArticleDOI
TL;DR: By evaluating the aggregated fronthaul traffic, this article shows the benefits of flexible centralization and gives guidelines on how to set up the fr onthaul network to avoid over- or under-dimensioning.
Abstract: Cloud radio access networks promise considerable benefits compared to decentralized network architectures, but they also put challenging requirements on the fronthaul and backhaul network. Flexible centralization can relax these requirements by adaptively assigning different parts of the processing chain to either the centralized baseband processors or the base stations based on the load situation, user scenario, and availability of fronthaul links. In this article, we provide a comprehensive overview of different functional split options and analyze their specific requirements. We compare these requirements to available fronthaul technologies, and discuss the convergence of fronthaul and backhaul technologies. By evaluating the aggregated fronthaul traffic, we show the benefits of flexible centralization and give guidelines on how to set up the fronthaul network to avoid over- or under-dimensioning.

Journal ArticleDOI
TL;DR: A cost-effective hybrid RF/free-space optical (FSO) solution to combine the advantages of RF backhauls (low cost, NLOS applications) and FSO backhauling (high-rate, low latency) is proposed.
Abstract: The rapid pace of demand for mobile data services and the limited supply of capacity in the current wireless access networks infrastructure are leading network operators to increase the density of base station deployments to improve network performance. This densification, made possible by small-cell deployment, also brings a novel set of challenges, specifically related to the cost of ownership, in which backhaul is of primary concern. This article proposes a cost-effective hybrid RF/free-space optical (FSO) solution to combine the advantages of RF backhauls (low cost, NLOS applications) and FSO backhauls (high-rate, low latency). To first illustrate the cost advantages of the RF backhaul solution, the first part of this article presents a business case of NLOS wireless RF backhaul, which has a low cost of ownership as compared to other backhaul candidates. RF backhaul, however, is limited by latency problems. On the other side, an FSO solution, which offers better latency and higher data rate than RF backhauls, remains sensitive to weather and nature conditions (e.g., rain, fog). To combine RF and FSO advantages, the second part of this article proposes a lowcost hybrid RF/FSO solution, wherein base stations are connected to each other using either optical fiber or hybrid RF/FSO links. This part addresses the problem of minimizing the cost of backhaul planning under reliability, connectivity, and data rate constraints, and proposes choosing the appropriate cost-effective backhaul connection between BSs (i.e., either OF or hybrid RF/FSO) using graph theory techniques.

Journal ArticleDOI
TL;DR: This article presents a comprehensive analysis on obtaining CSI in H-CRANs, and recognizes seven challenges in channel estimation that are caused by a large number of channel parameters, heterogeneity of access nodes, and the time delays among different nodes.
Abstract: As an emerging system architecture, heterogeneous cloud radio access networks (H-CRANs) can improve system capacity, enlarge coverage, and enhance energy/spectral efficiency. Meanwhile, this newborn architecture also brings many open problems for traditional topics, including synchronization, channel estimation, and data detection. In this article, we present a comprehensive analysis on obtaining CSI in H-CRANs. Specifically, we recognize seven challenges in channel estimation that are caused by a large number of channel parameters, heterogeneity of access nodes in H-CRANs, and the time delays among different nodes. Several research directions for handling these challenges are also proposed, for example, array signal processing and channel compression can eliminate the number of channel estimates, while channel prediction and modification for high-speed railway communications and adaptive downlink array from uplink measurements excel in overcoming the non-reciprocity in channel parameters.

Journal ArticleDOI
TL;DR: An algorithmic approach to the new design challenges for the dense heterogeneous Cloud-RAN based on convex optimization is provided, and a twostage framework to solve general large-scale conveX optimization problems is presented, which is amenable to parallel implementation in the cloud data center.
Abstract: The heterogeneous cloud radio access network (Cloud-RAN) provides a revolutionary way to densify radio access networks. It enables centralized coordination and signal processing for efficient interference management and flexible network adaptation. Thus it can resolve the main challenges for next-generation wireless networks, including higher energy efficiency and spectral efficiency, higher cost efficiency, scalable connectivity, and low latency. In this article we will provide an algorithmic approach to the new design challenges for the dense heterogeneous Cloud-RAN based on convex optimization. As problem sizes scale up with the network size, we will demonstrate that it is critical to take unique structures of design problems and inherent characteristics of wireless channels into consideration, while convex optimization will serve as a powerful tool for such purposes. Network power minimization and channel state information acquisition will be used as two typical examples to demonstrate the effectiveness of convex optimization methods. Then we will present a twostage framework to solve general large-scale convex optimization problems, which is amenable to parallel implementation in the cloud data center.

Journal ArticleDOI
TL;DR: This paper focuses on dimming mechanisms that can be implemented in VLC systems to save energy and provide precise illumination control, and the motivation behind this control mechanism.
Abstract: As a new generation green lighting source, the light emitting diode (LED) is rapidly replacing traditional incandescent and fluorescent light sources. Apart from providing energy savings, the use of LED lighting technology creates scope for an innovative optical wireless communication technology known as visible light communication (VLC), which takes advantage of the superior modulation capability of LEDs to transmit data through a wireless channel. VLC is capable of concurrently providing communication as well as illumination. For making commercial implementation of VLC feasible, it is necessary to incorporate it with dimming schemes that will provide energy savings, moods, and increase the aesthetic value of the place using this technology. However, general dimming techniques have an adverse effect on communication since they limit the achievable data rate of a VLC link. This drives the necessity of formulating efficient dimming techniques, which will create a balance between the two most basic functions of VLC: illumination and communication. This paper focuses on dimming mechanisms that can be implemented in VLC systems to save energy and provide precise illumination control. The motivation behind this control mechanism, current challenges in practical implementation, driver circuitry, recent progress, and future prospects are also concisely presented.

Journal ArticleDOI
TL;DR: A hierarchical cloud computing architecture is proposed to enhance performance by adding a mobile dynamic cloud formed by powerful mobile devices to a traditional general static cloud to increase the capacity of a mobile network.
Abstract: The emerging heterogeneous mobile network architecture is designed for an increasing amount of traffic, quality requirements, and new mobile cloud computing demands. This article proposes a hierarchical cloud computing architecture to enhance performance by adding a mobile dynamic cloud formed by powerful mobile devices to a traditional general static cloud. A mobile dynamic cloud is based on heterogeneous wireless architecture where device-to-device communication is used for data transmission between user devices. The main advantage of the proposed architecture is an increase in overall capacity of a mobile network through improved channel utilization and traffic offloading from Long Term Evolution-Advanced to device-to-device communication links. Simulations show that the proposed architecture increases the capacity of a mobile network by up to 10 percent depending on the conditions and amount of offloaded data. The offloading probability is also evaluated by taking into consideration the number of devices in the cloudlet and the content matching values. We have gained insight into how content similarity affects offloading probability much more than the number of devices in a cloudlet.

Journal ArticleDOI
TL;DR: This article designs a centralized controller to manage physical devices and provide an interface for data collection, transmission, and processing to develop a more flexible health surveillance application that is full of personalization.
Abstract: With the increasingly serious problem of the aging population, creating an efficient and real-time health management and feedback system based on the healthcare Internet of Things (HealthIoT) is an urgent need. Specifically, wearable technology and robotics can enable a user to collect the required human signals in a comfortable way. HealthIoT is the basic infrastructure for realizing health surveillance, and should be flexible to support multiple application demands and facilitate the management of infrastructure. Therefore, enlightened by the software defined network, we put forward a smart healthcare oriented control method to software define health monitoring in order to make the network more elastic. In this article, we design a centralized controller to manage physical devices and provide an interface for data collection, transmission, and processing to develop a more flexible health surveillance application that is full of personalization. With these distinguished characteristics, various applications can coexist in the shared infrastructure, and each application can demand that the controller customize its own data collection, transmission, and processing as required, and pass the specific configuration of the physical device. This article discusses the background, advantages, and design details of the architecture proposed, which is achieved by an open-ended question and a potential solution. It opens a new research direction of HealthIoT and smart homes.

Journal ArticleDOI
TL;DR: The architecture of MCS is introduced and its unique characteristics and advantages over traditional wireless sensor networks, which result in inapplicability of most existing WSN security solutions are discussed.
Abstract: Smartphones and other trendy mobile wearable devices are rapidly becoming the dominant sensing, computing and communication devices in peoples’ daily lives. Mobile crowd sensing is an emerging technology based on the sensing and networking capabilities of such mobile wearable devices. MCS has shown great potential in improving peoples’ quality of life, including healthcare and transportation, and thus has found a wide range of novel applications. However, user privacy and data trustworthiness are two critical challenges faced by MCS. In this article, we introduce the architecture of MCS and discuss its unique characteristics and advantages over traditional wireless sensor networks, which result in inapplicability of most existing WSN security solutions. Furthermore, we summarize recent advances in these areas and suggest some future research directions.