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The fifth generation (5G) mobile network is standardized and developed to explore the mobile market beyond 2020. In response to the diverse strategies of 5G deployment, five alternative network architectures have been proposed to 3GPP by different mobile operators. To fulfill the urgent deployment requirement from some operators, an early drop of 5G, termed as non-standalone (NSA) new radio (NR), was completed at the end of 2017. After that, the standardization of a new 5G system, including th standalone (SA) new radio access network, was finished in June 2018. This article analyzes and compares the SA NR and NSA NR deployment modes in terms of coverage, network capability, interworking between 4G and 5G, complexity and cost of network deployment, and the latest industry progress. NSA NR performs better in interworking performance in the initial phase, while SA NR performs better in network capabilities, device performance, simple network deployment, and cost efficiency. 5G SA NR is recommended for operators who have the ambition to explore new opportunities in the vertical and enterprise markets.

To meet the demands of mobile networks toward 2020, 5G has emerged. Compared to 4G, the 5G network will be deployed in higher-frequency bands, such as 3.5 GHz. Meanwhile, in order to save costs, operators expect to deploy the 5G network by reusing the legacy sites of 4G networks. Note that the coverage of base stations decreases with the increase of carrier frequency, and coverage enhancement techniques are required in 5G to cope with the coverage loss. In this article, coverage enhancement techniques are first analyzed. A field trial adopting pre-commercial 5G systems is then set up to assess the coverage performance. The analysis along with the promising field trial results indicate that the coverage of the 3.5 GHz frequency band can be guaranteed in the 5G network deployed with 4G legacy sites.

Full-duplex (FD) communications with simultaneous transmission and reception on the same carrier have long been deemed a promising way to boost spectrum efficiency, but hindered by the techniques for self-interference cancellation (SIC). Recent breakthroughs in analog and digital signal processing yield the feasibility of over 100 dB SIC capability, and make it possible for FD communications to demonstrate nearly doubled spectrum efficiency for pointto- point links. Now it is time to shift at least partially our focus to FD networking, such as in cellular networks. FD networking has more complicated interference environments. Therefore, its performance improvement is not that straightforward compared with half-duplex networking. Before putting FD networking into practice, we need to understand to which scenarios FD communications should be applied under the current technology maturity, how bad the performance will be if we do nothing to deal with the newly introduced interference, and most importantly, how much improvement could be achieved after applying advanced interference management solutions. We will discuss all these questions in this article. In particular, we will investigate advanced interference management solutions, including power control and user scheduling, and show that up to 91 percent spectrum efficiency gain and 110 percent energy efficiency gain of FD cellular networks over its HD counterpart can be achieved by applying these solutions.

The explosive increase of mobile traffic demands higher spectrum efficiency for future wireless communications. By properly configuring a 2-dimensional (2D) antenna array at the basestation, the system capacity can be improved with 3 dimensional (3D) multiuser Multiple Input and Multiple Output (MIMO) techniques without modifying the terminal antennas. Therefore, the signal will propagate in a 3D space with angle dispersion in both horizontal and vertical planes. Due to its role in facilitating research and development of 3D MIMO technology, the 3D fading channel model is receiving increasing attention. However, existing fading channel models mostly focus on the azimuth angle characteristics, while neglecting the elevation angle impact. This article provides a state of the art review on 3D fading channel models, emphasizing research related to the elevation angle. We also report some recent field measurements for 3D MIMO and investigate the comprehensive propagation characteristics of the elevation angle.

The articles in this special section focus on 5G mobile communication. With initial commercialization expected in 2020, fifth generation (5G) mobile communications is gathering increased interest and momentum around the world. Following discussions on the 5G vision and key requirements such as high data rate, low latency, and massive connectivity, various candidate technologies have been proposed and investigated. These new technologies include massive antenna technologies to provide beamforming gain and support increased capacity, new waveforms to flexibly accommodate various services and applications with different requirements, and new multiple access schemes to support massive connections. From a spectrum point of view, there is also increased interest in the use of spectrum above 6 GHz for 5G mobile communications.

LTE-Advanced extends the capabilities originally developed in LTE within the 3GPP. Carrier aggregationis the most significant, albeit complex, improvement provided by LTE-Advanced. Bandwidths from various portions of the spectrum are logically concatenated resulting in a virtual block of a much larger band, enabling increased data throughput. Additionally, enhancements to MIMO antenna techniques in the uplink and downlink further increase the data throughput. Cell coverage is improved by means of relay nodes, which connect to donor eNode-Bs. To cope with the many varieties of cell types and sizes (macro, pico, femto), intercell interference control is enhanced to handle these heterogeneous networks. Operators hope to leverage LTE-Advanced to offer their mobile wireless customers a vastly superior user experience.

The rapid growth of mobile applications in recent years has created a need for wideband wireless communication. The only predictable trend is that data-rate and QoS requirements will increase rapidly. This demand is pushing time-division-synchronous code-division multiple access (TD-SCDMA) to evolve in order to provide higher and higher data rates. This article presents the evolution map from TD-SCDMA to future terrestrial universal radio environment (FuTURE) TDD in China. The evolution includes four phases: low chip rate (LCR), high-speed downlink/uplink packet access (HSxPA)/TD-SCDMA EV 1x, long-term evolution (LTE) TDD, and FuTURE beyond 3G TDD. The main features of each phase are described in detail. By introducing the new technologies into the system step by step, for example, multiple input and multiple output (MIMO), orthogonal frequency-division multiplexing (OFDM), TD-SCDMA system can evolve to FuTURE B3G TDD smoothly, and provide high-data-rate services with low cost, low latency, and improved coverage and capacity.