## 4 Empirical Study
### Key Technology Network Analysis  
For identifying key technologies, the researchers used patent data from the CPC system for analysis. The centrality of a node was determined by its closeness centrality, betweenness centrality, and fragmentation centrality. All three are effective indicators of centrality. [PERSON] (1998) used the concepts of key player problem-positive and key player problem-negative to define key players in a network. Key player problem-positive refers to a certain node's connectivity to other nodes compared with that of its peers. It is primarily determined by the node's closeness centrality. Key player problem-negative designates a certain node's role in maintaining network stability, that is, the likelihood of network fragmentation once that node is removed. Key player problem-negative is primarily determined by betweenness centrality and fragmentation centrality. The network model of the key technologies is presented in Figure 1, and the key CPCs are presented in Table 4.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**CPC** & \begin{tabular}{c} **Closeness** \\ **Centrality** \\ \end{tabular} & **CPC** & \
\begin{tabular}{c} **Betweenness** \\ **Centrality** \\ \end{tabular} & **CPC** &
\begin{tabular}{c} **Fragmentation** \\ **Centrality** \\ \end{tabular} \\ \hline H04W88 & 90 & H04W88 & 696.273 & H04W88 & 0.470 \\ H04W72 & 80 & H04B10 & 470.019 & H04B10 & 0.468 \\ H04Q11 & 78.5 & H04L5 & 367.544 & H04L5 & 0.467 \\ H04W84 & 77.5 & H04W72 & 297.066 & H04Q11 & 0.466 \\ H04L5 & 77 & H04Q11 & 286.362 & H04W72 & 0.465 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Top five CPC codes of 5G optical networks.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ranking** & **Patentee** & \
\begin{tabular}{c} **Number of** \\ **Patents** \\ \end{tabular} & **Percentage** &
\begin{tabular}{c} **Average Age** \\ **of Patents** \\ \end{tabular} \\ \hline
1 & Huawei Technologies CO., LTD. & 11 & 8.87\% & 1 \\
2 & Smart Mobile INC. & 8 & 6.45\% & 4 \\
3 & Telefonaktiebolaget LM Ericsson (publ) & 7 & 5.65\% & 1 \\
4 & AT\&T Intellectual Property I, L.P. & 6 & 4.84\% & 2 \\
5 & Inphi Corporation & 6 & 4.84\% & 2 \\
6 & Dali Research (Northwind) LLC & 6 & 4.84\% & 3 \\
7 & Futurewei Technologies INC. & 5 & 4.03\% & 2 \\
8 & Corning Optical Communications LLC & 5 & 4.03\% & 2 \\
9 & Google LLC & 3 & 2.42\% & 2 \\
10 & Nippon Telegraph and Telephone Corporation & 3 & 2.42\% & 2 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Number of approved patents of the top 10 patentees.  
Table 4 shows that H04W88, H04W72, H04Q11, and H04L5 are the top five technology domains in 5G, as indicated by their closeness, betweenness, and fragmentation centrality. These results suggest that the key technologies for 5G optical networks mostly lie in the domains of wireless communication network facilities and local resource management (H04W88 and H04W72), selecting arrangements for multiplex systems (H04Q11), and arrangements affording multiple uses of the transmission path (H04L5). Accordingly, the most critical 5G optical network technologies are those related to wireless communication network facilities and multiplex communication systems. In particular, the advancement of optical component technology (e.g., semiconductor lasers, optical amplifiers, and optical filters) paved the way for the flourishing of multiplex communication system technology, which enabled the provision of diversified and high-capacity broadband services. The development of these relevant technologies should dominate the development trends of 5G optical networks in the future.