# From 5G to 6G--Challenges, Technologies, and Applications
###### Abstract  
As the deployment of 5G mobile radio networks gains momentum across the globe, the wireless research community is already planning the successor of 5G. In this paper, we highlight the shortcomings of 5G in meeting the needs of more data-intensive, low-latency, and ultra-high-reliability applications. We then discuss the salient characteristics of the 6G network following a hierarchical approach including the social, economic, and technological aspects. We also discuss some of the key technologies expected to support the move towards 6G. Finally, we quantify and summarize the research work related to beyond 5G and 6G networks through an extensive search of publications and research groups and present a possible timeline for 6G activities.  
3 GPP; 6G; artificial intelligence; beyond 5G; edge computing; next-gen; THz +
Footnote †: journal: _Future Internet_  
5G standards, such as dealing with signal propagation loss, which will inevitably increase with the use of higher frequencies (beyond 20 GHz), or maintaining efficient network management under increasingly complicated networks [5, 6].  
Although research in the beyond 5G area has picked up momentum in recent years with many surveys and discussions in the literature, we differentiate ourselves by considering a hierarchical approach, providing a comprehensive review of the different aspects of 6G-enabling technologies and the current major research initiatives and publications related to 6G. Moreover, we discuss many of the deep learning methods to be used in 6G, provide an accurate count of papers discussing next-gen networks between 2015 and 2020, and show how the depth of the discussions on 6G have changed over the years. Additionally, we divided the published 6G surveys into seven categories: waveform, antennas, artificial intelligence (AI), security, blockchain, management, and architecture, and provide an up-to-date listing of 6G surveys at the time of writing of this paper. In this paper, we discuss the challenges facing 5G and how they are expected to stimulate the research towards 6G. In particular, the main contributions of this work are as follows:  
* We highlight the main limitations of 5G and its key technologies;
* We present a holistic view of 6G that includes the social, technical, and economic aspects;
* We provide a comprehensive review of recent research activities and projects related to 6G;
* We summarize the literature work on 6G's vision and its potential technologies, as well as the timeline for 6G's roll out on the market;
* We discuss 6G's downsides, from the physical and mental health implications for individuals, to the impact on the Earth's ecosystems, and speculate about its existence in the future.  
The rest of the paper is organized as follows: Section 2 discusses the main shortcomings of 5G, while Section 3 discusses the aspects, requirements, and enabling technologies of 6G. Section 4 presents a summary of the current research related to 6G, and finally, Section 5 provides the conclusion. We show in Figure 2 the outline of our paper.  
Figure 1: A brief overview of the history of wireless communication networks (TD: time division, FD: frequency division, CD: code division).  
Figure 2: Paper outline.