The fifth generation (5G) wireless communication networks are being deployed worldwide from 2020 and more capabilities are in the process of being standardized, such as mass connectivity, ultra-reliability, and guaranteed low latency. However, 5G will not meet all requirements of the future in 2030 and beyond, and sixth generation (6G) wireless communication networks are expected to provide global coverage, enhanced spectral/energy/cost efficiency, better intelligence level and security, etc. To meet these requirements, 6G networks will rely on new enabling technologies, i.e., air interface and transmission technologies and novel network architecture, such as waveform design, multiple access, channel coding schemes, multi-antenna technologies, network slicing, cell-free architecture, and cloud/fog/edge computing. Our vision on 6G is that it will have four new paradigm shifts. First, to satisfy the requirement of global coverage, 6G will not be limited to terrestrial communication networks, which will need to be complemented with non-terrestrial networks such as satellite and unmanned aerial vehicle (UAV) communication networks, thus achieving a space-air-ground-sea integrated communication network. Second, all spectra will be fully explored to further increase data rates and connection density, including the sub-6 GHz, millimeter wave (mmWave), terahertz (THz), and optical frequency bands. Third, facing the big datasets generated by the use of extremely heterogeneous networks, diverse communication scenarios, large numbers of antennas, wide bandwidths, and new service requirements, 6G networks will enable a new range of smart applications with the aid of artificial intelligence (AI) and big data technologies. Fourth, network security will have to be strengthened when developing 6G networks. This article provides a comprehensive survey of recent advances and future trends in these four aspects. Clearly, 6G with additional technical requirements beyond those of 5G will enable faster and further communications to the extent that the boundary between physical and cyber worlds disappears.

第五代（5G）无线通信网络将从2020年开始在全球范围内部署，并且更多功能正在标准化过程中，例如大规模连接，超可靠性和保证的低延迟。但是，5G将无法满足2030年及以后的所有需求，并且第六代（6G）无线通信网络有望提供全球覆盖范围，增强的频谱/能源/成本效率，更高的智能水平和安全性等。根据这些要求，6G网络将依赖于新的使能技术，即空中接口和传输技术以及新颖的网络体系结构，例如波形设计，多址，信道编码方案，多天线技术，网络切片，无小区体系结构以及云/雾/边缘计算。我们对6G的愿景是它将有四个新的模式转变。首先，为了满足全球覆盖的要求，6G不仅限于地面通信网络，还需要与非地面网络（例如卫星和无人机（UAV）通信网络）相辅相成，从而实现空空陆海综合通信网络。其次，将充分探索所有频谱，以进一步提高数据速率和连接密度，包括6 GHz以下，毫米波（mmWave），太赫兹（THz）和光学频带。第三，面对由于使用极其异构的网络，多样化的通信场景，大量的天线，宽带宽以及新的服务需求而生成的大型数据集，6G网络将借助人工智能（AI）和大数据技术，实现一系列新的智能应用。第四，开发6G网络时必须加强网络安全性。本文对这四个方面的最新进展和未来趋势进行了全面的调查。显然，在物理世界和网络世界之间的界限消失的情况下，具有5G以外的其他技术要求的6G将使通信更加快速和进一步。