## 1 Introduction
### Challenges and Motivation-Existing Cellular Technologies Cannot Support Tactile Internet Yet
\begin{table}
\begin{tabular}{p{113.8 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Use Case** & & **Availability** & **Cycle Time** & **Payload Size** & \begin{tabular}{c} **Number of** \\ **Devices** \\ \end{tabular} & **Typical Service Area** \\ \hline Motion control & \begin{tabular}{c} Printing \\ machine \\ \end{tabular} & \textgreater{}99.9999\% & \textless{}2 ms & 20 bytes & 100 & 100 m \(\times\) 100 m \(\times\) 30 m \\  & \begin{tabular}{c} Machine tool \\ Packaging \\ machine \\ \end{tabular} & \textgreater{}99.9999\% & \textless{}1 ms & 50 bytes & \textasci{}20 & 15 m \(\times\) 15 m \(\times\) 15 m \\ \hline Mobile robots & \begin{tabular}{c} Cooperative \\ motion control \\ Video-operated \\ remote control \\ \end{tabular} & \textgreater{}99.9999\% & 1 ms & 40–250 bytes & 100 & \textless{}1 km\({}^{2}\) \\ \hline Mobile control & \begin{tabular}{c} Assembly \\ robots or \\ panels with \\ safety functions \\ \end{tabular} & \begin{tabular}{c} Assembly \\ robots or \\ milling \\ machines \\ \end{tabular} & \textgreater{}99.9999\% & 4–8 ms & 40–250 bytes & 4 & 10 m \(\times\) 10 m \\ \cline{2-6}  & \begin{tabular}{c} Mobile cranes \\ \end{tabular} & \begin{tabular}{c} \textgreater{}99.9999\% \\ \end{tabular} & 12 ms & 40–250 bytes & 2 & 40 m \(\times\) 60 m \\ \hline Process automation & \
\begin{tabular}{c} \textgreater{}99.999\% \\ (process monitoring) \\ \end{tabular} & \textgreater{}99.99\% & \textgreater{}50 ms &
\begin{tabular}{c} Varies \\ \end{tabular} & 10,000 devices per km\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison of peak data rate versus latency [18]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Term** & **Definition** & **Source** \\ \hline \multirow{4}{*}{Internet of Things (IoT)} & IoT can be realized as a new form of network created by physical devices. In this type of network, the physical devices are called things. Each thing is embedded with sensing systems and associated software which enable the connection and data exchange with other things over the internet. & [27] \\ \hline \multirow{4}{*}{Tactile internet (IT)} & According to the International Telecommunication Union (ITU), TI can be realized as the next generation of internet network. This new generation of internet is based on the combination of ultra-low latency, extremely high network availability, reliability, and security. Ultimately, TI will enable the advanced human-machine interface (HMI), based on the interaction of humans with the new TI environment through human senses. & [29] \\ \hline \multirow{4}{*}{Tactile internet (IT)} & This notation refers to the mobile network generations, encapsulating the corresponding communication protocols. Concretely, “G” refers to “generation”, whereas the numerical value refers to the number of the generation. For example, 5G refers to the fifth generation of mobile networks & [30] \\ \cline{1-1}  & & \\ \cline{1-1}  & & \\ \cline{1-1}  & & \\ \cline{1-1}  & & \\ \cline{1-1}  & & \\ \cline{1-1}  & & \\ \cline{1-1}  & & \\ \cline{1-1}  & & \\ \hline \hline \end{tabular}  
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Table 2: Glossary of Key Concepts. Figure 3: Verticals sectors’ capabilities and requirements spider charts [26]. Based on the abovementioned identified challenges, the contribution of this state-of-the-art paper can be summarized as follows:  
1. It provides a state-of-the-art review on 5G and related key technologies under the framework of Industry 4.0 and beyond. 2. It identifies three important challenges faced by industrial stakeholders in the volatile global marketplace. 3. It highlights the fact that existing cellular technologies cannot support the tactile internet yet. 4. It clearly introduces the era beyond 5G. The well-known Figure 1 that presents the evolution of mobile network technologies has been elaborated and includes the main features of the 6G technology for the years to come. 5.