Whilst the fifth-generation (5G) systems are being rolled out across the globe, researchers have turned their attention to the exploration of radical next-generation solutions. At this early evolutionary stage we survey five main research facets of this field, namely {\em Facet~1: next-generation architectures, spectrum and services, Facet~2: next-generation networking, Facet~3: Internet of Things (IoT), Facet~4: wireless positioning and sensing, as well as Facet~5: applications of deep learning in 6G networks.} In this paper, we have provided a critical appraisal of the literature of promising techniques ranging from the associated architectures, networking, applications as well as designs. We have portrayed a plethora of heterogeneous architectures relying on cooperative hybrid networks supported by diverse access and transmission mechanisms. The vulnerabilities of these techniques are also addressed and carefully considered for highlighting the most of promising future research directions. Additionally, we have listed a rich suite of learning-driven optimization techniques. We conclude by observing the evolutionary paradigm-shift that has taken place from pure single-component bandwidth-efficiency, power-efficiency or delay-optimization towards multi-component designs, as exemplified by the twin-component ultra-reliable low-latency mode of the 5G system. We advocate a further evolutionary step towards multi-component Pareto optimization, which requires the exploration of the entire Pareto front of all optiomal solutions, where none of the components of the objective function may be improved without degrading at least one of the other components.

翻译：尽管第五代(5G)系统正在全球各地推出,研究人员已将其注意力转向探索激进的下一代解决方案。在这个早期进化阶段,我们调查了该领域的五大研究方面,即:Femfacet~1:下一代结构、频谱和服务,Facet~2:下一代网络,Facet~2:Facet~3:物联网,Facet~4:无线定位和感知,以及Facet~5:在6G网络中应用深层次学习。 }在本文件中,我们批判性地评估了从相关架构、网络、应用程序和设计等有希望的技术组成部分的文献。我们描绘了大量依赖不同访问和传输机制支持的合作混合网络的多样化结构,这些技术的脆弱性也得到了探讨和认真考虑,以突出最有希望的未来研究方向。此外,我们列举了一套丰富的学习驱动优化技术。我们通过观察从纯单一成份的带宽效率、功率、最差或整个延迟的变异化模式转变,从一个更低的系统转向一个多成型的系统,而要求一个双向多成型的成型的成型的成型的成型系统,我们可进一步的成型的成型的成型的成型的成型的成型式系统需要一个双形式,要求一个可推进的成型的成型的成型的成型的成型式的成型式的成型式,我们制。我们制式的成型式系统需要一个可进一步的成型式式式的压式式式式的系统需要一个双向一个可进一步的成形式,一个双向式的成型式,需要一个可推进式式式的多式式的成形式式式的成形式式式式式的成形式的成形式式式式式式,要求所有的成形式的成形式的成形式的制制制制制制制制制制制制制制制制制制制制制制制制制的系统,以制制制制制制的系统,以制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制制