Since 5G networks are expensive in terms of equipment, require large investments during construction, consume large amounts of power and have high operating costs, co-location and sharing have become a new approach to operator network development and operation. This paper first introduces the networking architecture and interoperability interface of inter-network roaming in core networks, followed by the key procedures and specifications of inter-network roaming, and then analyzes the registration procedures and terminal mobility management in roaming areas. Finally, a proposal for inter-network roaming commercialization is presented, and the correctness and feasibility of the scheme are verified through interactive experiments between home 4G and visited 5G as well as between home 5G and visited 5G.

Ubiquitous Internet of Things (UIoT) is required a 3-D network that stretches from space to air to earth. It involves numerous network components, such as satellites, HAPs, UAVs, terrestrial cellular networks, data centers, terrestrial gateways, as well as sharing and openness among operators. Correspondingly, wireless spectrum sharing becomes essential to energy efficiency and, thus, has to be investigated for green UIoT. Meanwhile, both blockchain and sixth-generation mobile communication technology hybrid cloud are recently intriguing technologies, and the enormous potential of combining the two has grown in prominence. For the reason of dependability and security, these two technologies are proposed to apply to spectrum sharing among UIoT devices. Particularly the blockchain’s unique smart contract technology can well complete the spectrum sharing procedure, as verified by the numerical results from our simulation study.

This paper looks into the realization of digital twin (DT) technology in unmanned aerial vehicle (UAV) networks. We propose, in particular, a framework for DT-based UAV applications in which distinct jobs in the digital twin interact with UAVs in the physical world via task manager scheduling. Furthermore, we investigate the use of 3D mmWave Radar imaging on UAVs and apply it to the process of radio frequency (RF) characterizing. After that, the method of 3D ray-tracing is employed to accomplish channel modelling of UAVs, which reflects RF domain digital twin match. Finally, we present numerical results to demonstrate that our developed digital twin platform can provide accurate RF presentation of UAV and therefore accomplish smart operating and administration of the actual UAV network.

In recent years, with the energy consumption and environmental degradation, science and technology embarked on a path of sustainable development. In this situation, 5G green communication system has been widely used. This paper introduces the application of RF reflectors to 5G mmWave, where line‐of‐sight (LoS) blockage is a major hindrance for the coverage. In particular, we investigate the lab measurement of RF reflectors, which is a critical step from the theory to the practice. Furthermore, through the lab measurement, a 3D near‐field range migration (RM) imaging algorithm for MIMO array configuration is proposed, and the sampling scheme is improved to save the computation time while providing high‐quality images.

This work focuses on the analysis for multicast services in fifth-generation (5G) wireless communication system. We investigate the physical- layer wireless multicast technology in massive multi-input multi-output (MIMO) mutual coupling channel model, and proposed the hybrid unicast/multicast transmission system. The mutual coupling channel model is adopted to describe the channel characteristics under the linear antenna array scenario and the rectangular antenna array scenario. The proposed hybrid transmission scheme adopts multicast beamforming in the multicast groups as well as multi-user MIMO (MU-MIMO) linear precoding in the unicast group to increase system throughput. The null-space method based interference cancellation is further performed between each group to eliminate signal leakage generated from each group. Comparisons between two types of antenna array configurations, different channel models, linear precoding as well as multicast beamforming, and user grouping strategies for multicast services are presented and analyzed by simulation.

In this paper, we propose a pilot-aided channel estimation scheme for Orthogonal Frequency-Division Multiplexing (OFDM) systems where channels are assumed to be both time-varying and sparse. Basis Expansion Models (BEM) are often used to model and reconstruct time-varying channel taps. In this paper, the framework of BEM is applied to OFDM systems with time-varying sparse channels. A new method to detect the positions of significant taps is proposed based on the use of Constant Amplitude Zero Auto Correlation (CAZAC) sequence. Based on the results of detection, BEM based estimation is implemented to estimate the detected taps. The numerical simulations illustrate that the proposed two-step estimation scheme for significant channel taps outperforms direct estimation methods for all the channel taps and also this method can reduce the required pilots and thus reduce the computational load and improve the spectral efficiency.