As of today, the fifth generation (5G) mobile communication system has been rolled out in many countries and the number of 5G subscribers already reaches a very large scale. It is time for academia and industry to shift their attention towards the next generation. At this crossroad, an overview of the current state of the art and a vision of future communications are definitely of interest. This article thus aims to provide a comprehensive survey to draw a picture of the sixth generation (6G) system in terms of drivers, use cases, usage scenarios, requirements, key performance indicators (KPIs), architecture, and enabling technologies. First, we attempt to answer the question of "Is there any need for 6G?" by shedding light on its key driving factors, in which we predict the explosive growth of mobile traffic until 2030, and envision potential use cases and usage scenarios. Second, the technical requirements of 6G are discussed and compared with those of 5G with respect to a set of KPIs in a quantitative manner. Third, the state-of-the-art 6G research efforts and activities from representative institutions and countries are summarized, and a tentative roadmap of definition, specification, standardization, and regulation is projected. Then, we identify a dozen of potential technologies and introduce their principles, advantages, challenges, and open research issues. Finally, the conclusions are drawn to paint a picture of "What 6G may look like?". This survey is intended to serve as an enlightening guideline to spur interests and further investigations for subsequent research and development of 6G communications systems.

The Road Towards 6G: A Comprehensive Survey

As of today, the fifth generation (5G) mobile communication system has been rolled out in many countries and the number of 5G subscribers already reaches a very large scale It is time for academia and industry to shift their attention towards the next generation At this crossroad, an overview of the current state of the art and a vision of future communications are definitely of interest This article thus aims to provide a comprehensive survey to draw a picture of the sixth generation (6G) system in terms of drivers, use cases, usage scenarios, requirements, key performance indicators (KPIs), architecture, and enabling technologies First, we attempt to answer the question of “Is there any need for 6G?” by shedding light on its key driving factors, in which we predict the explosive growth of mobile traffic until 2030, and envision potential use cases and usage scenarios Second, the technical requirements of 6G are discussed and compared with those of 5G with respect to a set of KPIs in a quantitative manner Third, the state-of-the-art 6G research efforts and activities from representative institutions and countries are summarized, and a tentative roadmap of definition, specification, standardization, and regulation is projected Then, we identify a dozen of potential technologies and introduce their principles, advantages, challenges, and open research issues Finally, the conclusions are drawn to paint a picture of “What 6G may look like?” This survey is intended to serve as an enlightening guideline to spur interests and further investigations for subsequent research and development of 6G communications systems

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This article aims to provide a comprehensive overview for key issues in broadband LEO satellite communication systems. First of all, the network architecture is introduced, which is the basis of the whole system. The space-based LEO system with ISL, which requires a small number of ground gateways, is the focus. In this system, the satellite constellation design is important with impact on key system performances such as coverage. Two popular LEO constellations, the walker Delta and Star constellations, are introduced. Given satellite constellations, proper beam coverage schemes should be employed at satellites to provide seamless coverage all over the world. A hybrid wide and spot beam coverage scheme is presented, where the LEO provides a wide beam for large area coverage and several steering spot beams for highspeed data access. Moreover, special coverage schemes should be designed in broadband LEO systems for the interference coordination between LEO and GEO. To protect GEO communications, LEO satellites should be turned off if they cause interference to GEO. In this case, to provide services for users covered by the turned-off LEO satellites, a progressive pitch method and a coverage expanding method can be employed. Finally, the coverage performance of LEO is also closely related to resource management schemes. The global resource management for broadband LEO systems is complicated, involving a large amount of data, and a two-level management structure should be employed. Using this structure, an NMC with powerful storage and processing capabilities is employed to carry out the first-level management, making strategies based on all information collected from the whole system. Then satellite base stations with limited capabilities are employed to respond to the strategies generated by NMC in real time.

Broadband LEO Satellite Communications: Architectures and Key Technologies

Digital Soviet Union : the Russian national segment of the Internet as a closed national network shaped by strategic cultural ideas

With a ten-year horizon from concept to reality, it is time now to start thinking about what will the sixth-generation (6G) mobile communications be on the eve of the fifth-generation (5G) deployment. To pave the way for the development of 6G and beyond, we provide 6G visions in this paper. We first introduce the state-of-the-art technologies in 5G and indicate the necessity to study 6G. By taking the current and emerging development of wireless communications into consideration, we envision 6G to include three major aspects, namely, mobile ultra-broadband, super Internet-of-Things (IoT), and artificial intelligence (AI). Then, we review key technologies to realize each aspect. In particular, teraherz (THz) communications can be used to support mobile ultra-broadband, symbiotic radio and satellite-assisted communications can be used to achieve super IoT, and machine learning techniques are promising candidates for AI. For each technology, we provide the basic principle, key challenges, and state-of-the-art approaches and solutions.

6G Visions: Mobile ultra-broadband, super internet-of-things, and artificial intelligence

Internet of Things (IoT) is one of the evolutionary directions of the Internet. This paper focuses on the low earth orbit (LEO) satellite constellation-based IoT services for their irreplaceable functions. In many cases, IoT devices are distributed in remote areas (e.g., desert, ocean, and forest) in some special applications, they are placed in some extreme topography, where are unable to have direct terrestrial network accesses and can only be covered by satellite. Comparing with the traditional geostationary earth orbit (GEO) systems, LEO satellite constellation has the advantages of low propagation delay, small propagation loss and global coverage. Furthermore, revision of existing IoT protocol are necessary to enhance the compatibility of the LEO satellite constellation-based IoT with terrestrial IoT systems. In this paper, we provide an overview of the architecture of the LEO satellite constellation-based IoT including the following topics: LEO satellite constellation structure, efficient spectrum allocation, heterogeneous networks compatibility, and access and routing protocols.

Gengxin Zhang

Papers

LEO Satellite Constellation for Internet of Things