Traditional ultra-dense wireless networks are recommended as a complement for cellular networks and are deployed in partial areas, such as hotspot and indoor scenarios. Based on the massive multiple-input multi-output antennas and the millimeter wave communication technologies, the 5G ultra-dense cellular network is proposed to deploy in overall cellular scenarios. Moreover, a distribution network architecture is presented for 5G ultra-dense cellular networks. Furthermore, the backhaul network capacity and the backhaul energy efficiency of ultra-dense cellular networks are investigated to answer an important question, that is, how much densification can be deployed for 5G ultra-dense cellular networks. Simulation results reveal that there exist densification limits for 5G ultra-dense cellular networks with backhaul network capacity and backhaul energy efficiency constraints.

5G Ultra-Dense Cellular Networks

The exponential growth and availability of data in all forms is the main booster to the continuing evolution in the communications industry. The popularization of traffic-intensive applications including high definition video, 3-D visualization, augmented reality, wearable devices, and cloud computing defines a new era of mobile communications. The immense amount of traffic generated by today’s customers requires a paradigm shift in all aspects of mobile networks. Ultradense network (UDN) is one of the leading ideas in this racetrack. In UDNs, the access nodes and/or the number of communication links per unit area are densified. In this paper, we provide a survey-style introduction to dense small cell networks. Moreover, we summarize and compare some of the recent achievements and research findings. We discuss the modeling techniques and the performance metrics widely used to model problems in UDN. Also, we present the enabling technologies for network densification in order to understand the state-of-the-art. We consider many research directions in this survey, namely, user association, interference management, energy efficiency, spectrum sharing, resource management, scheduling, backhauling, propagation modeling, and the economics of UDN deployment. Finally, we discuss the challenges and open problems to the researchers in the field or newcomers who aim to conduct research in this interesting and active area of research.

Ultra-Dense Networks: A Survey

The standardization of fifth generation (5G) communications has been completed, and the 5G network should be commercially launched in 2020. As a result, the visioning and planning of 6G communications has begun, with an aim to provide communication services for the future demands of the 2030s. Here, we provide a vision for 6G that could serve as a research guide in the post-5G era. We suggest that human-centric mobile communications will still be the most important application of 6G and the 6G network should be human centric. Thus, high security, secrecy and privacy should be key features of 6G and should be given particular attention by the wireless research community. To support this vision, we provide a systematic framework in which potential application scenarios of 6G are anticipated and subdivided. We subsequently define key potential features of 6G and discuss the required communication technologies. We also explore the issues beyond communication technologies that could hamper research and deployment of 6G. This Perspective provides a vision for sixth generation (6G) communications in which human-centric mobile communications are considered the most important application, and high security, secrecy and privacy are its key features.

What should 6G be

The standardization of fifth generation (5G) communications has been completed, and the 5G network should be commercially launched in 2020. As a result, the visioning and planning of sixth generation (6G) communications has begun, with an aim to provide communication services for the future demands of the 2030s. Here we provide a vision for 6G that could serve a research guide in the post-5G era. We suggest that human-centric mobile communications will still be the most important application of 6G and the 6G network should be human centric. Thus, high security, secrecy, and privacy should be key features of 6G and should be given particular attention by the wireless research community. To support this vision, we provide a systematic framework in which potential application scenarios of 6G are anticipated and subdivided. We subsequently define key potential features of 6G and discuss the required communication technologies. We also explore the issues beyond communication technologies that could hamper research and deployment of 6G.

Device-to-Device (D2D) communication has emerged as a promising technology for optimizing spectral efficiency in future cellular networks. D2D takes advantage of the proximity of communicating devices for efficient utilization of available resources, improving data rates, reducing latency, and increasing system capacity. The research community is actively investigating the D2D paradigm to realize its full potential and enable its smooth integration into the future cellular system architecture. Existing surveys on this paradigm largely focus on interference and resource management. We review recently proposed solutions in over explored and under explored areas in D2D. These solutions include protocols, algorithms, and architectures in D2D. Furthermore, we provide new insights on open issues in these areas. Finally, we discuss potential future research directions.

A Survey of Device-to-Device Communications: Research Issues and Challenges

To tackle the 1000× mobile data challenge, the research towards the 5th generation of mobile cellular networks is currently ongoing. One clear enabler toward substantially improved network area capacities is the increasing level of network densification at different layers of the overall heterogeneous radio access system. Ultra-dense deployments, or DenseNets, seek to take network densification to a whole new level, where extreme spatial reuse is deployed. This article looks into DenseNets from the perspectives of different deployment strategies, covering the densification of the classical macro layer, extremely dense indoor femto layer, as well as outdoor distributed antenna system (DAS), which can be dynamically configured as a single microcell or multiple independent microcells. Also, the potential of a new indoor-to-outdoor service provisioning paradigm is examined. The different deployment solutions are analyzed from the network area spectral and network energy efficiency perspectives, with extreme densification levels, including both indoor and outdoor use scenarios. The obtained results indicate that dedicated indoor solutions with densely deployed femtocells are much more spectrumand energy-efficient approaches to address the enormous indoor capacity demands compared to densifying the outdoor macro layer, when the systems are pushed to their capacity limits. Furthermore, the dynamic outdoor DAS concept offers an efficient and capacity-adaptive solution to provide outdoor capacity, on demand, in urban areas.

Spectral and energy efficiency of ultra-dense networks under different deployment strategies

Network densification has been identified as one key enabling technology to address the 1000x mobile data challenge. This article analyzes network densification from the different deployment options perspective by looking into three mainstream technologies; Macrocells, Microcells, and Femtocells. The technologies are evaluated in a suburban neighborhood with modern residential houses. As majority of the data traffic in the network is believed to be generated by indoor users, we make a techno-economic analysis and comparison of the different deployment strategies from the indoor local area service provisioning viewpoint. Results show superior performance of low power indoor femtocell based deployment solutions in terms of coverage, capacity, energy and cost efficiency as compared to the outdoor solutions. Densifying the traditional pure Macro or Micro layers does provide improvement in the indoor coverage levels, however, due to the closer proximity of the co-channel interfering sites, the achievable capacity in the indoor environment deteriorates, which in turn also affects the energy and cost efficiency. These findings strongly motivate towards ultra dense deployments, based on indoor femtocell solutions, for addressing the local area capacity needs of the emerging future 5G networks.

Techno-economical analysis and comparison of legacy and ultra-dense small cell networks

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Impact of Macrocellular Network Densification on the Capacity, Energy and Cost Efficiency in Dense Urban Environment

This paper studies the coverage aspects of a low altitude platform (LAP) system that can form a temporary communication network. The system consists of multiple autonomous drones equipped with dual-band Wi-Fi access points (APs) with ad hoc capabilities to form a mesh network. The suitability of the LAP system is evaluated from the coverage point of view with calculations and simulations. The results show that more drones are needed to cover (dense) urban than rural environment and the drone altitude should also be higher in urban areas compared with the rural areas.

Coverage aspects of temporary LAP network

Modern houses and constructions use energy efficient building materials, like metal shielding and energy saving windows, to improve the thermal insulation and efficiency. However, such energy efficient building materials not only block the thermal radiation but also substantially increase the building penetration losses of the radio signals, forming thus a challenging problem in mobile cellular networks where majority of network elements are still located outdoors while more and more of the mobile data use takes place indoors. In this article, the use of frequency selective surface (FSS) is studied as one potential means to reduce the penetration loss while still maintaining high thermal insulation of the buildings. FSS structures build on a combination of either conducting patches or apertures in a thin conducting sheet arranged periodically in one or two dimensional array, and can be etched on the metal coating of energy saving windows that behave as electromagnetic filter. Thus, such energy saving windows incorporating FSS structures can potentially allow transmission of radio signals while still essentially retaining its major thermal insulation properties. The aim of this paper is to investigate the applicability of such FSS structures in realworld scenarios with actual field measurements in real mobile networks. First, double square-loop FSS structure which is transparent to GSM 900MHz and UMTS/HSPA 2100MHz frequency bands is developed and analyzed. The developed FSS structure is then fabricated using aluminum foil and tested and measured in both laboratory conditions as well as in real mobile networks and real buildings. In the mobile network measurements, the developed FSS prototype shows substantial improvements of the indoor signal strengths, in the order of 8-13 dB for GSM 900MHz band and 2-5 dB for UMTS/HSPA 2100MHz frequency band, compared to the uniform metal coating. This indicates that FSS structures can provide useful and feasible means to enhance the indoor signal levels in future energy efficient built environments, and thus substantially enhance the indoor coverage and capacity of wireless networks.

Syed Fahad Yunas

Papers

Spectral and energy efficiency of ultra-dense networks under different deployment strategies

Techno-economical analysis and comparison of legacy and ultra-dense small cell networks

Impact of Macrocellular Network Densification on the Capacity, Energy and Cost Efficiency in Dense Urban Environment

Coverage aspects of temporary LAP network

Applicability of Frequency Selective Surfaces to Enhance Mobile Network Coverage in Future Energy-Efficient Built Environments