## 4 Experimental Results and Comparative Analyses
### Empirical Analysis
Topic 17, '17_channel estimation_sparse_millimeter wave channel_deep learning', indicates that deep learning-based methods for sparse millimeter-wave channel estimation are emerging. In the context of 6G, millimeter-wave communication is crucial for achieving high-data-rate transmission. However, the complex channel environment poses challenges. Deep learning can potentially optimize channel estimation algorithms, improving signal reception and transmission quality. Topic 18, '18_millimeter wave radar_wave radar_doppler_target detection', suggests that millimeter-wave radar technology for Doppler target detection is on the rise. This is important for applications such as 6G-enabled autonomous driving, where precise target detection is essential for vehicle safety. By observing the TEM heatmap for NSTs, we can see how these topics' importance has changed over time. A topic with a low average proportion but a high growth rate, like these two, is considered a weak signal. Monitoring such topics helps stakeholders in the 6G industry anticipate future technological needs and invest in relevant research and development. Figure 5: _Cont._  
Figure 5: _Cont_. Figure 5: This figure shows overall trends and hierarchy clustering for 5 subjects. Figure 6: _Cont_. Some other examples in the RIS dataset are shown in the table. For instance, Topic 5, '5_terahertz_terahertz wave_vanadium dioxide_resonator', shows that the research on vanadium dioxide resonators for terahertz waves is emerging. Terahertz communication is a key technology for 6G, and vanadium dioxide's unique properties may enable the development of more efficient terahertz devices. Topic 10, '10_holographic_nano brick_micro nano optic_nano optic', indicates the potential of holographic nano-brick-based micro-nano optics in 6G. This could be applied to improve the performance of optical communication components in RIS systems. The heatmap of the TEM for RISs visually represents the development trends of these topics. It allows us to compare the growth rates and average proportions of different topics, facilitating the identification of technologies that are likely to have a significant impact on the future of RIS-related 6G applications. This information can guide companies in the 6G field to allocate resources more effectively and focus on technologies with high-growth potential. Regarding the ISAC dataset, Topic 15, '15_grating_waveguide_wavelength_coupler', implies that grating waveguide wavelength couplers are emerging as an important technology. These couplers can play a crucial role in optical-based integrated sensing and communication systems, enabling efficient coupling of optical signals. Topic 18, '18_millimeter wave_mimo_hybrid beamforming_mmwave', shows that millimeter-wave MIMO hybrid beamforming technology is gaining momentum. In 6G, MIMO technology com  
Figure 6: This figure shows overall trends for 5 subjects on the left-hand side (Strong Signal (4), Weak Signal (3), Potential Signal (2), Well-known but Non-strong Signal (1), No Signal or Unclassified (0)) and hierarchy clustering on the right-hand side. bined with hybrid beamforming can enhance communication capacity and signal coverage. The TEM heatmap for ISAC helps visualize the evolution of these topics. It provides a clear picture of which technologies are emerging and which are more established, enabling researchers and industry players to understand the technological landscape better. This understanding is vital for strategic planning, such as setting research priorities and formulating product development strategies in the ISAC domain of 6G. In the ISAGSC field, the TEM helps identify emerging trends such as laser communication in satellite systems and edge computing offloading in ground-integrated networks. Weak-signal topics like '12_laser communication_satellite laser_optical communication_leo satellite' and '19_edge_edge computing_offloading_ground integrated network' imply that these areas are emerging as important research directions.