## 4 Experimental Results and Comparative Analyses
### Empirical Analysis  
In the empirical analysis section of this study, our experiments were designed to comprehensively explore the technological evolution in the 6G field. We conducted DTM analysis on individual subject fields of five datasets in 6G, which included NSTs, RISs, ISAC, ISAGSC, and EAIs. Based on the concept of weak signal analysis, we calculated the TEM and heatmap to quantitatively identify the weak signals of 6G, which is an emerging technology in the near future. These results provide a deeper understanding of the technological evolution in the 6G field, enabling us to identify emerging technologies and trends. This information can support strategic decision-making in the industry, helping stakeholders to plan research and development directions and stay ahead in the highly competitive 6G market. Firstly, we adopted a BERTopic-based DTM to conduct an analysis of the overall trends for 6G technology. Figure 5 shows the top-ranked topics from the charts for five datasets. The topics with line chart visualizations were generated based on our DTM framework. Clearly, all the technologies that are displayed as top-rated topics have grown fast over the years. As we can see in the charts, in the new spectrum technology (NST) of 6G, the 'power \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Model** & **NSTs** & **RISs** & **ISAC** & **ISAGSC** & **EAIs** \\ \hline Baseline & 0.5968 & 0.6849 & 0.6775 & 0.6542 & 0.6647 \\ \hline Baseline + OPT & 0.8898 & 0.9080 & 0.9467 & 0.9241 & 0.9463 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: This table shows the comparisons of performances of averages of TD in the baseline model and baseline with hyperparameter optimizations. The elements highlighted in red in the table represent the maximum values in the corresponding columns. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Model** & **NSTs** & **RISs** & **ISAC** & **ISAGSC** & **EAIs** \\ \hline Baseline & 0.4900 & 0.4978 & 0.4749 & 0.4683 & 0.4615 \\ \hline Baseline + OPT & 0.7877 & 0.6511 & 0.5498 & 0.6412 & 0.5982 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: This table shows the comparison of performances of averages of TC in the baseline model and baseline with hyperparameter optimizations. The elements highlighted in red in the table represent the maximum values in the corresponding columns. amplifier_mixer_inductor_stage' has been rated as the top-most ranked topic recently. This is likely because the power amplifier is essential for boosting the signal power. Since 6G requires high-speed data transmission over long distances in a wider spectrum, a power amplifier can ensure that the signal can still be accurately detected after suffering from attenuation during propagation. The mixer is mainly responsible for frequency conversion. It enables the transformation of signals between different frequencies, which is beneficial for signal processing and transmission in the 6G new spectrum. Inductors, on the other hand, work with capacitors to form LC filters, filtering out unwanted signals and noise. They also play a role in energy storage and impedance matching. Similarly, we can easily identify the top-rated topics for the remaining four subjects from Figure 5, which are the 'dielectric substrate_metasurface antenna' for RISs, 'radar communication_ofdm' for ISAC,'satellite_network' for ISAGSC, and 'beam management' for EAIs. To further explore the technological evolution in the domain-specific fields in 6G, we employed TEMs associated with heatmaps to quantify the emergence of technological shifts in the five subjects of the patent datasets, as shown in Figure 6. The weak signals refer to the signals with a low average proportion but a high growth rate in the obtained topics, as shown in Table 7.  
For instance, in the NST dataset, the identified weak signals provide valuable insights into the emerging technological directions.