A brief overview of 5G research activities
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paper_title: What Will 5G Be?

paper_content:

What will 5G be? What it will not be is an incremental advance on 4G. The previous four generations of cellular technology have each been a major paradigm shift that has broken backward compatibility. Indeed, 5G will need to be a paradigm shift that includes very high carrier frequencies with massive bandwidths, extreme base station and device densities, and unprecedented numbers of antennas. However, unlike the previous four generations, it will also be highly integrative: tying any new 5G air interface and spectrum together with LTE and WiFi to provide universal high-rate coverage and a seamless user experience. To support this, the core network will also have to reach unprecedented levels of flexibility and intelligence, spectrum regulation will need to be rethought and improved, and energy and cost efficiencies will become even more critical considerations. This paper discusses all of these topics, identifying key challenges for future research and preliminary 5G standardization activities, while providing a comprehensive overview of the current literature, and in particular of the papers appearing in this special issue.
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paper_title: 5G: Personal mobile internet beyond what cellular did to telephony

paper_content:

Cellular technology has dramatically changed our society and the way we communicate. First it impacted voice telephony, and then has been making inroads into data access, applications, and services. However, today potential capabilities of the Internet have not yet been fully exploited by cellular systems. With the advent of 5G we will have the opportunity to leapfrog beyond current Internet capabilities.
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paper_title: An energy efficient and spectrum efficient wireless heterogeneous network framework for 5G systems

paper_content:

In this article we explore a system framework of cooperative green heterogeneous networks for 5G wireless communication systems. We first survey the state-of-the-art on spectrum efficiency (SE), energy efficiency (EE), and quality of service (QoS) based mobile association, multi-layer interference management and power control, network wide cooperation and dynamic resource allocation for heterogeneous wireless networks. We also present the system framework of cooperative green heterogeneous networks, which aims at balancing and optimizing SE, EE, and QoS in heterogeneous wireless networks. We discuss the design principles and show some preliminary performance results on the tradeoffs among SE, EE, and QoS. Finally, we identify the technical challenges that remain in the cooperative green heterogeneous network design. The presented wireless system framework is expected to advance the understandings of the critical technical issues toward energy and spectrum efficient 5G wireless communication systems.
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paper_title: The LEXNET Project: Wireless Networks and EMF: Paving the Way for Low-EMF Networks of the Future

paper_content:

While, according to the World Health Organization, no adverse health effects of radio-frequency (RF) electromagnetic fields (EMFs) have been established to date, EMF exposure from wireless communication networks is nonetheless often cited as a major cause of public concern and is frequently given considerable media coverage. This article presents the results of a new survey on RF-EMF exposure risk perception together with a comprehensive overview of the EMF footprint of existing and emerging networks. On the basis of these findings, we then put forward the rationale for EMF-aware networking. Subsequently, we highlight the gaps in existing systems, which impede EMF-aware networking, and outline the key concepts of the recently launched European Union (EU) Seventh Framework Programme (FP7) Integrated Project Low-EMF Exposure Future Networks (LEXNET): a new, all-encompassing, population-based metric of exposure and ways it can be used for low-EMF, quality of service (QoS)-aware network optimization.
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paper_title: 5GNOW: non-orthogonal, asynchronous waveforms for future mobile applications

paper_content:

This article provides some fundamental indications about wireless communications beyond LTE/LTE-A (5G), representing the key findings of the European research project 5GNOW. We start with identifying the drivers for making the transition to 5G networks. Just to name one, the advent of the Internet of Things and its integration with conventional human-initiated transmissions creates a need for a fundamental system redesign. Then we make clear that the strict paradigm of synchronism and orthogonality as applied in LTE prevents efficiency and scalability. We challenge this paradigm and propose new key PHY layer technology components such as a unified frame structure, multicarrier waveform design including a filtering functionality, sparse signal processing mechanisms, a robustness framework, and transmissions with very short latency. These components enable indeed an efficient and scalable air interface supporting the highly varying set of requirements originating from the 5G drivers.
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paper_title: Cache in the air: exploiting content caching and delivery techniques for 5G systems

paper_content:

The demand for rich multimedia services over mobile networks has been soaring at a tremendous pace over recent years. However, due to the centralized architecture of current cellular networks, the wireless link capacity as well as the bandwidth of the radio access networks and the backhaul network cannot practically cope with the explosive growth in mobile traffic. Recently, we have observed the emergence of promising mobile content caching and delivery techniques, by which popular contents are cached in the intermediate servers (or middleboxes, gateways, or routers) so that demands from users for the same content can be accommodated easily without duplicate transmissions from remote servers; hence, redundant traffic can be significantly eliminated. In this article, we first study techniques related to caching in current mobile networks, and discuss potential techniques for caching in 5G mobile networks, including evolved packet core network caching and radio access network caching. A novel edge caching scheme based on the concept of content-centric networking or information-centric networking is proposed. Using trace-driven simulations, we evaluate the performance of the proposed scheme and validate the various advantages of the utilization of caching content in 5G mobile networks. Furthermore, we conclude the article by exploring new relevant opportunities and challenges.
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paper_title: Millimeter-wave beamforming as an enabling technology for 5G cellular communications: theoretical feasibility and prototype results

paper_content:

The ever growing traffic explosion in mobile communications has recently drawn increased attention to the large amount of underutilized spectrum in the millimeter-wave frequency bands as a potentially viable solution for achieving tens to hundreds of times more capacity compared to current 4G cellular networks. Historically, mmWave bands were ruled out for cellular usage mainly due to concerns regarding short-range and non-line-of-sight coverage issues. In this article, we present recent results from channel measurement campaigns and the development of advanced algorithms and a prototype, which clearly demonstrate that the mmWave band may indeed be a worthy candidate for next generation (5G) cellular systems. The results of channel measurements carried out in both the United States and Korea are summarized along with the actual free space propagation measurements in an anechoic chamber. Then a novel hybrid beamforming scheme and its link- and system-level simulation results are presented. Finally, recent results from our mmWave prototyping efforts along with indoor and outdoor test results are described to assert the feasibility of mmWave bands for cellular usage.
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paper_title: Network densification: the dominant theme for wireless evolution into 5G

paper_content:

This article explores network densification as the key mechanism for wireless evolution over the next decade. Network densification includes densification over space (e.g, dense deployment of small cells) and frequency (utilizing larger portions of radio spectrum in diverse bands). Large-scale cost-effective spatial densification is facilitated by self-organizing networks and intercell interference management. Full benefits of network densification can be realized only if it is complemented by backhaul densification, and advanced receivers capable of interference cancellation.
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paper_title: Applications of self-interference cancellation in 5G and beyond

paper_content:

Self-interference cancellation invalidates a long-held fundamental assumption in wireless network design that radios can only operate in half duplex mode on the same channel. Beyond enabling true in-band full duplex, which effectively doubles spectral efficiency, self-interference cancellation tremendously simplifies spectrum management. Not only does it render entire ecosystems like TD-LTE obsolete, it enables future networks to leverage fragmented spectrum, a pressing global issue that will continue to worsen in 5G networks. Self-interference cancellation offers the potential to complement and sustain the evolution of 5G technologies toward denser heterogeneous networks and can be utilized in wireless communication systems in multiple ways, including increased link capacity, spectrum virtualization, any-division duplexing (ADD), novel relay solutions, and enhanced interference coordination. By virtue of its fundamental nature, self-interference cancellation will have a tremendous impact on 5G networks and beyond.
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paper_title: Five Disruptive Technology Directions for 5G

paper_content:

New research directions will lead to fundamental changes in the design of future 5th generation (5G) cellular networks. This paper describes five technologies that could lead to both architectural and component disruptive design changes: device-centric architectures, millimeter Wave, Massive-MIMO, smarter devices, and native support to machine-2-machine. The key ideas for each technology are described, along with their potential impact on 5G and the research challenges that remain.
---
paper_title: 5G: Personal mobile internet beyond what cellular did to telephony

paper_content:

Cellular technology has dramatically changed our society and the way we communicate. First it impacted voice telephony, and then has been making inroads into data access, applications, and services. However, today potential capabilities of the Internet have not yet been fully exploited by cellular systems. With the advent of 5G we will have the opportunity to leapfrog beyond current Internet capabilities.
---
paper_title: 5GNOW: non-orthogonal, asynchronous waveforms for future mobile applications

paper_content:

This article provides some fundamental indications about wireless communications beyond LTE/LTE-A (5G), representing the key findings of the European research project 5GNOW. We start with identifying the drivers for making the transition to 5G networks. Just to name one, the advent of the Internet of Things and its integration with conventional human-initiated transmissions creates a need for a fundamental system redesign. Then we make clear that the strict paradigm of synchronism and orthogonality as applied in LTE prevents efficiency and scalability. We challenge this paradigm and propose new key PHY layer technology components such as a unified frame structure, multicarrier waveform design including a filtering functionality, sparse signal processing mechanisms, a robustness framework, and transmissions with very short latency. These components enable indeed an efficient and scalable air interface supporting the highly varying set of requirements originating from the 5G drivers.
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paper_title: Networks and devices for the 5G era

paper_content:

Mobile services based on 4G LTE services are steadily expanding across global markets, providing subscribers with the type of responsive Internet browsing experience that previously was only possible on wired broadband connections. With more than 200 commercial LTE networks in operation as of August 2013 [1], LTE subscriptions are expected to exceed 1.3 billion by the end of 2018 [2]. LTE's rapid uptake, based on exponential growth in network data traffic, has opened the industry's eyes to an important reality: the mobile industry must deliver an economically sustainable capacity and performance growth strategy; one that offers increasingly better coverage and a superior user experience at lower cost than existing wireless systems, including LTE. This strategy will be based on a combination of network topology innovations and new terminal capabilities. Simple network economics also require that the industry's strategy enable new services, new applications, and ultimately new opportunities to monetize the user experience. To address these pressing requirements, many expert prognosticators are turning their attention to future mobile broadband technologies and standards (i.e., 5G) as well as evolutions of the 3GPP's existing LTE standard and IEEE 802.11 standards.
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paper_title: Cloud technologies for flexible 5G radio access networks

paper_content:

The evolution toward 5G mobile networks will be characterized by an increasing number of wireless devices, increasing device and service complexity, and the requirement to access mobile services ubiquitously. Two key enablers will allow the realization of the vision of 5G: very dense deployments and centralized processing. This article discusses the challenges and requirements in the design of 5G mobile networks based on these two key enablers. It discusses how cloud technologies and flexible functionality assignment in radio access networks enable network densification and centralized operation of the radio access network over heterogeneous backhaul networks. The article describes the fundamental concepts, shows how to evolve the 3GPP LTE architecture, and outlines the expected benefits.
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paper_title: The requirements, challenges, and technologies for 5G of terrestrial mobile telecommunication

paper_content:

In this article, we summarize the 5G mobile communication requirements and challenges. First, essential requirements for 5G are pointed out, including higher traffic volume, indoor or hotspot traffic, and spectrum, energy, and cost efficiency. Along with these changes of requirements, we present a potential step change for the evolution toward 5G, which shows that macro-local coexisting and coordinating paths will replace one macro-dominated path as in 4G and before. We hereafter discuss emerging technologies for 5G within international mobile telecommunications. Challenges and directions in hardware, including integrated circuits and passive components, are also discussed. Finally, a whole picture for the evolution to 5G is predicted and presented.
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paper_title: An energy efficient and spectrum efficient wireless heterogeneous network framework for 5G systems

paper_content:

In this article we explore a system framework of cooperative green heterogeneous networks for 5G wireless communication systems. We first survey the state-of-the-art on spectrum efficiency (SE), energy efficiency (EE), and quality of service (QoS) based mobile association, multi-layer interference management and power control, network wide cooperation and dynamic resource allocation for heterogeneous wireless networks. We also present the system framework of cooperative green heterogeneous networks, which aims at balancing and optimizing SE, EE, and QoS in heterogeneous wireless networks. We discuss the design principles and show some preliminary performance results on the tradeoffs among SE, EE, and QoS. Finally, we identify the technical challenges that remain in the cooperative green heterogeneous network design. The presented wireless system framework is expected to advance the understandings of the critical technical issues toward energy and spectrum efficient 5G wireless communication systems.
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paper_title: Device-to-device communication in 5G cellular networks: challenges, solutions, and future directions

paper_content:

In a conventional cellular system, devices are not allowed to directly communicate with each other in the licensed cellular bandwidth and all communications take place through the base stations. In this article, we envision a two-tier cellular network that involves a macrocell tier (i.e., BS-to-device communications) and a device tier (i.e., device-to-device communications). Device terminal relaying makes it possible for devices in a network to function as transmission relays for each other and realize a massive ad hoc mesh network. This is obviously a dramatic departure from the conventional cellular architecture and brings unique technical challenges. In such a two-tier cellular system, since the user data is routed through other users? devices, security must be maintained for privacy. To ensure minimal impact on the performance of existing macrocell BSs, the two-tier network needs to be designed with smart interference management strategies and appropriate resource allocation schemes. Furthermore, novel pricing models should be designed to tempt devices to participate in this type of communication. Our article provides an overview of these major challenges in two-tier networks and proposes some pricing schemes for different types of device relaying.
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paper_title: Cooperative distributed optimization for the hyper-dense small cell deployment

paper_content:

The fifth generation mobile networks will be developed to improve area spectral and energy efficiency, and provide uniform user experience. Hyper-dense small cell deployment can move devices closer to the wireless network and satisfy 5G system requirements. The main challenge of this network deployment results from the random deployment, dynamic on-off, flexible connection to cellular core networks, and flat system architecture of 5G systems. Therefore, conventional network planning and radio resource management, which depend on a central control node, cannot be applied to small cell networks. In this article some cooperative distributed radio resource management algorithms for time synchronization, carrier selection, and power control are discussed for hyper-dense small cell deployment.
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Title: A Brief Overview of 5G Research Activities
Section 1: INTRODUCTION
Description 1: Introduce the increasing demand for wireless technology advancements leading to 5G, and outline the paper's coverage of various 5G research activities, projects, and literature.

Section 2: EUROPEAN 5G PROJECTS
Description 2: Provide an overview of significant European Union projects and initiatives focused on 5G research, listing specific objectives and technological advancements.

Section 3: LITERATURE REVIEW ON 5G
Description 3: Summarize recent magazine articles, academic papers, and white papers that discuss various aspects of 5G technology, including key technological trends and future directions.

Section 4: 5G White Papers
Description 4: Review major white papers from leading companies and organizations, summarizing their visions, technological innovations, and predicted impacts of 5G.

Section 5: CONCLUSION
Description 5: Conclude the paper by summarizing the findings from the projects and literature, highlighting the emerging common features and technological advancements of 5G.