5G Wireless: Technology, Standard and Practice

  5G wireless technology is developing at an explosive rate and is one of the biggest areas of research within academia and industry. With 2G, 3G and 4G, the peak service rate is the dominant metric that distinguishes these three generations. 5G will significantly increase the peak service rate but will also dramatically increase energy efficiency, frequency efficiency, spectral efficiency, and efficiency of other resources. It will dramatically increase flexibility, capacity, coverage, compatibility and convergence. In this way, it will satisfy the increasing demands of emerging big⁃data, cloud, machine⁃to⁃machine, and other applications. The successful development and deployment of 5G technologies will be challenging and will require huge effort from industry, academia, standardization organizations, and regulatory authorities.

  This special issue deals with the application, technology, and standardization of 5G and aims to stimulate research and development of 5G by providing a unique forum for scientists, engineers, broadcasters, manufacturers, software developers, and other related professionals. The topics addressed in this special issue include system architecture, protocols, physical layer (downlink and uplink), air interface, cell acquisition, scheduling and rate adaption, access procedures, relaying, and spectrum allocation. The call⁃for⁃papers for this special issue attracted a number of excellent submissions. After two⁃round reviews, six papers were selected for publication. These papers are organized in two groups. The first group comprises three overview papers that outline technical aspects of 5G. The second group comprises three papers that provide new algorithms and theoretical analyses that can be used in the development of 5G wireless systems.

  The first paper, “5G: Vision, Scenarios and Enabling Technologies,” presents an excellent vision for 5G wireless communications systems, which are expected to be standardized around 2020. The paper states that service ubiquity is the key requirement of 5G from the end⁃user’s prospective and is necessary to support a vast mesh of connections for human⁃to⁃human, human⁃to⁃machine, and machine⁃to⁃machine communications in an energy⁃efficient way. This paper discusses various technologies designed to improve radio link efficiency, expand operating bandwidth, and increase cell density. With these technologies, 5G systems can accommodate a massive volume of traffic, and this is fundamental for service ubiquity and supporting a massive number of connections, as outlined in the 5G vision of this paper. This paper also discusses the transition to intelligent cloud, in particular, cloud coordination of network access, which enables a flatter architecture.

  The second paper, “Towards 5th Generation Wireless Communication Systems,” discusses the targeted 5G system, including its driver, requirements, and candidate technologies that might help achieve its intended goals. Drawing on recent results obtained by the author’s research team, the author discusses detection of and access to free spectrum over bands of a heterogeneous nature, extreme densification of networks (mass base station deployments), extreme increase in the number of antennas in transmitter arrays and their interaction with a novel waveform, integration of both wireless and optical sides of telecom networks, and design of wireless networks from the perspective of complex systems science.

  The third paper, “Signal Processing Techniques for 5G: An Overview,” gives an overview of the main signal⁃processing techniques being developed for 5G wireless communications. At the beginning of this paper, the author reviews six orthogonal and non⁃orthogonal waveform⁃generation and modulation schemes: generalized frequency⁃division multiplexing (GFDM), filter bank multi⁃carrier (FBMC) transmission, universal filtered multicarrier (UFMC) transmission, bi⁃orthogonal frequency division multiplexing (BFDM), sparse code multiple access (SCMA) and non⁃orthogonal multiple access (NOMA). Then, the author discusses spatial signal processing algorithms and implementations of massive multiple⁃input multiple⁃output (massive MIMO), 3D beamforming and diversity, and multiplexing based on orbital angular momentum (OAM). The author also briefly reviews aspects of signal processing for other emerging techniques in 5G, such as millimeter wave, cloud radio access networks, full duplex mode, and digital RF processing.

  The fourth paper, “Energy⁃Efficient Large⁃Scale Antenna Systems with Hybrid Digital⁃Analog Beamforming Structure,” provides both theoretical analysis and simulations on the design of a large⁃scale antenna system (LSAS) with beamforming (BF), which is believed to significantly increase energy efficiency (EE) and spectral efficiency (EE) in a 5G wireless system. The paper investigates the optimal antenna configuration in an N × M hybrid BF structure, where N is the number of transceivers, and M is the number of antennas per transceiver. In such a structure, analog BF is introduced for each transceiver, and digital BF is introduced across N transceivers. The emphasis of this paper is EE⁃SE optimization when NM is fixed and when N and M are independent. The EE⁃SE relationship at “green” points is first investigated, then the effect of M on EE at a given SE is analyzed. In both cases, the authors show that there is an optimal M that provides the best EE for a given SE. The authors also discuss the optimal M when there is severe inter⁃user interference. These proposed analyses and results will be very useful in designing and deploying such LSAS for 5G.

  The fifth paper, “An Optimal Lifetime Utility Routing for 5G and Energy⁃Harvesting Wireless Networks,” looks at wireless sensor networking as a representative of all the different kinds of links involved in 5G. This paper also addresses energy efficiency. The authors propose an energy⁃harvest⁃aware route⁃selection method that incorporates harvest availability and energy storage capacity into routing decisions. In other words, the harvest⁃aware routing problem is formulated as a linear programming problem with a utility⁃based objective function that balances two conflicting routing objectives so that the proposed algorithm extends network lifetime. In addition, the authors investigate the effects of various network factors, such as topology, energy consumption rates, and prediction error, on energy savings.

  The sixth paper, “Interference⁃Cancellation Scheme for Multilayer Cellular Systems,” discusses interference cancellation, which is a challenging problem in a heterogeneous network that has coexisting multilayer cells, multiple standards and multiple application systems. First, an interference signal model that takes into account channel effect as well as time and frequency error is presented. An interference⁃cancellation scheme based on this model is then investigated. Following that, a method for compensating the timing and carrier frequency offset of an interference signal is presented. In the last step of processing, interference is mitigated by subtracting the estimation of interference signal. Computer simulation shows that the proposed interference⁃cancellation algorithm significantly improves performance in different channel conditions.

  As we conclude the introduction of this special issue, we would like to thank all authors for their valuable contributions, and we express our sincere gratitude to all the reviewers for their timely and insightful comments submitted papers. It is hoped that the contents in this special issue are informative and useful from the aspects of technology, standardization, and implementation.