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.

What Will 5G Be

The global bandwidth shortage facing wireless carriers has motivated the exploration of the underutilized millimeter wave (mm-wave) frequency spectrum for future broadband cellular communication networks. There is, however, little knowledge about cellular mm-wave propagation in densely populated indoor and outdoor environments. Obtaining this information is vital for the design and operation of future fifth generation cellular networks that use the mm-wave spectrum. In this paper, we present the motivation for new mm-wave cellular systems, methodology, and hardware for measurements and offer a variety of measurement results that show 28 and 38 GHz frequencies can be used when employing steerable directional antennas at base stations and mobile devices.

Millimeter Wave Mobile Communications for 5G Cellular: It Will Work!

There is considerable pressure to define the key requirements of 5G, develop 5G standards, and perform technology trials as quickly as possible. Normally, these activities are best done in series but there is a desire to complete these tasks in parallel so that commercial deployments of 5G can begin by 2020. 5G will not be an incremental improvement over its predecessors; it aims to be a revolutionary leap forward in terms of data rates, latency, massive connectivity, network reliability, and energy efficiency. These capabilities are targeted at realizing high-speed connectivity, the Internet of Things, augmented virtual reality, the tactile internet, and so on. The requirements of 5G are expected to be met by new spectrum in the microwave bands (3.3-4.2 GHz), and utilizing large bandwidths available in mm-wave bands, increasing spatial degrees of freedom via large antenna arrays and 3-D MIMO, network densification, and new waveforms that provide scalability and flexibility to meet the varying demands of 5G services. Unlike the one size fits all 4G core networks, the 5G core network must be flexible and adaptable and is expected to simultaneously provide optimized support for the diverse 5G use case categories. In this paper, we provide an overview of 5G research, standardization trials, and deployment challenges. Due to the enormous scope of 5G systems, it is necessary to provide some direction in a tutorial article, and in this overview, the focus is largely user centric, rather than device centric. In addition to surveying the state of play in the area, we identify leading technologies, evaluating their strengths and weaknesses, and outline the key challenges ahead, with research test beds delivering promising performance but pre-commercial trials lagging behind the desired 5G targets.

5G : A tutorial overview of standards, trials, challenges, deployment, and practice

Millimeter wave (mmWave) holds promise as a carrier frequency for fifth generation cellular networks. Because mmWave signals are sensitive to blockage, prior models for cellular networks operated in the ultra high frequency (UHF) band do not apply to analyze mmWave cellular networks directly. Leveraging concepts from stochastic geometry, this paper proposes a general framework to evaluate the coverage and rate performance in mmWave cellular networks. Using a distance-dependent line-of-site (LOS) probability function, the locations of the LOS and non-LOS base stations are modeled as two independent non-homogeneous Poisson point processes, to which different path loss laws are applied. Based on the proposed framework, expressions for the signal-to-noise-and-interference ratio (SINR) and rate coverage probability are derived. The mmWave coverage and rate performance are examined as a function of the antenna geometry and base station density. The case of dense networks is further analyzed by applying a simplified system model, in which the LOS region of a user is approximated as a fixed LOS ball. The results show that dense mmWave networks can achieve comparable coverage and much higher data rates than conventional UHF cellular systems, despite the presence of blockages. The results suggest that the cell size to achieve the optimal SINR scales with the average size of the area that is LOS to a user.

Coverage and Rate Analysis for Millimeter-Wave Cellular Networks

Femtocells, despite their name, pose a potentially large disruption to the carefully planned cellular networks that now connect a majority of the planet's citizens to the Internet and with each other. Femtocells - which by the end of 2010 already outnumbered traditional base stations and at the time of publication are being deployed at a rate of about five million a year - both enhance and interfere with this network in ways that are not yet well understood. Will femtocells be crucial for offloading data and video from the creaking traditional network? Or will femtocells prove more trouble than they are worth, undermining decades of careful base station deployment with unpredictable interference while delivering only limited gains? Or possibly neither: are femtocells just a "flash in the pan"; an exciting but short-lived stage of network evolution that will be rendered obsolete by improved WiFi offloading, new backhaul regulations and/or pricing, or other unforeseen technological developments? This tutorial article overviews the history of femtocells, demystifies their key aspects, and provides a preview of the next few years, which the authors believe will see a rapid acceleration towards small cell technology. In the course of the article, we also position and introduce the articles that headline this special issue.

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Femtocells: Past, Present, and Future

The proliferation of internet-connected mobile devices will continue to drive growth in data traffic in an exponential fashion, forcing network operators to dramatically increase the capacity of their networks. To do this cost-effectively, a paradigm shift in cellular network infrastructure deployment is occurring away from traditional (expensive) high-power tower-mounted base stations and towards heterogeneous elements. Examples of heterogeneous elements include microcells, picocells, femtocells, and distributed antenna systems (remote radio heads), which are distinguished by their transmit powers/ coverage areas, physical size, backhaul, and propagation characteristics. This shift presents many opportunities for capacity improvement, and many new challenges to co-existence and network management. This article discusses new theoretical models for understanding the heterogeneous cellular networks of tomorrow, and the practical constraints and challenges that operators must tackle in order for these networks to reach their potential.

Heterogeneous cellular networks: From theory to practice

The exemplary embodiments of the invention provide at least a method and an apparatus to determine a beacon signal for a network node, where the network node is configured to connect with a cluster of access points in a wireless communication network, and where the beacon signal identifies the cluster; and send the beacon signal towards the wireless communication network. Further, the exemplary embodiments of the invention provide at least a method and an apparatus to determine a dominant access point of a cluster of access points based on signaling from at least one access point associated with the cluster of access points; and in response to the determining, direct communications towards the dominant access point of the cluster of access points.

Millimeter Wave Access Architecture with Cluster of Access Points

To meet the explosive growth in traffic during the next twenty years, 5G systems using local area networks need to be developed. These systems will comprise of small cells and will use extreme cell densification. The use of millimeter wave (Mmwave) frequencies, in particular from 20 GHz to 90 GHz, will revolutionize wireless communications given the extreme amount of available bandwidth. However, the different propagation conditions and hardware constraints of Mmwave (e.g., the use of RF beamforming with very large arrays) require reconsidering the modulation methods for Mmwave compared to those used below 6 GHz. In this paper we present ray-tracing results, which, along with recent propagation measurements at Mmwave, all point to the fact that Mmwave frequencies are very appropriate for next generation, 5G, local area wireless communication systems. Next, we propose null cyclic prefix single carrier as the best candidate for Mmwave communications. Finally, systemlevel simulation results show that with the right access point deployment peak rates of over 15 Gbps are possible at Mmwave along with a cell edge experience in excess of 400 Mbps.

Air interface design and ray tracing study for 5G millimeter wave communications

Availability of large untapped spectrum resources in the millimeter wave (Mmwave) band is suitable for providing a gigabit experience with true local feel using high capacity small cells. Unlike traditional cellular systems, millimeter wave transmissions do not benefit from diffraction and dispersion making it difficult for them to propagate around obstacles thus resulting in higher shadowing loss. They also have less favorable link budgets due to lower power amplifier (PA) output powers and greater pathloss at these higher frequencies. Also, current costs of the Mmwave circuits are higher, but the costs will become much lower when the technology becomes mainstream. One advantage of millimeter wave, however, is that the smaller wavelengths allow for the fabrication of antenna arrays having a much higher number of antenna elements in a much smaller area than is typical at microwave bands. In this article, we outline a framework for Beyond-4G (B-4G) local area network in the millimeter wave band for both access and backhaul including air-interface, antenna-arrays and IC technology. It is shown that Mmwave B-4G small cell technology can provide peak and cell edge rates greater than 10 Gbps and 100 Mbps respectively with latency less than 1msec for local area network.

Moving Towards Mmwave-Based Beyond-4G (B-4G) Technology

Millimeterwave band is a promising candidate for 5th generation wireless access technology to deliver peak and cell-edge data rates of the order of 10 Gbps and 100 Mbps, respectively, and to meet the future capacity demands The main advantages of the millimeterwave band are availability of large blocks of contiguous bandwidth and the opportunity of using large antenna arrays composed of very small antenna elements to provide large antenna gains The line-of-sight operation requirement in this band, due to its unique propagation characteristics, makes it necessary to build the network with enough redundancy of access points and the users may have to frequently handoff from one access point to another whenever its radio link is disrupted by obstacles In this paper we investigate the handoff rate in such an access network Based on analysis of various deployment scenarios, we observe that, typical average handoff interval is several seconds, although for certain types of user actions the average handoff interval can be as low as 075 sec

Mark Cudak

Papers

Heterogeneous cellular networks: From theory to practice

Millimeter Wave Access Architecture with Cluster of Access Points

Air interface design and ray tracing study for 5G millimeter wave communications

Moving Towards Mmwave-Based Beyond-4G (B-4G) Technology

Handoff Rates for Millimeterwave 5G Systems