# A Survey on the Impact of Intelligent Surfaces in the Terahertz Communication Channel Models
## 5 Discussions and Research Directions
### Research Directions  
To meet the 6G implementation requirements, IS will play an essential role in being able to decrease the signal attenuation THz and enable SRE [156; 157]. Although significant progress has been made in several studies in THz signal research, some focus specifically on GHz technology [158; 159]. On the other hand, it is crucial to consider that performance evaluations can be produced more accurately by considering THz signals instead of GHz signals. According to study [91], the THz band is subject to high attenuation and has a more limited propagation range than the GHz band. Critical reports can contain project cost analysis, device design, computational load, and IS sizing. In addition, research has modeled the influence of different IS elements on the transmitter and IS and IS and receiver links as independent, while in practice, they may be correlated. This relationship could exist depending on the distance between the IS elements. In addition to dealing with such a complex situation, researchers may find new obstacles to plan IS to maintain or exceed the performance metrics reported in previous works. Knowledge of the channel makes it possible for transmitters and receivers to use this information to decide when to transmit in order to increase the probability of decoding at the receiver [160; 161]. In addition, correctly modeling the propagation environment by considering both small-scale and large-scale fading makes the system more realistic [162]. Therefore, channel models are crucial for systems requiring high QoS. Comparisons between deterministic and statistical models for channel modeling THz were studied in Section 3. However, despite advances in the various proposals for propagation models at THz, the properties of materials in the high THz band remain unknown [163]. In addition, the frequency selectivity phenomenon in the THz channel deserves special attention due to the distortion in the pulse shape [164]. The statistical model must consider this phenomenon, as it may lengthen the pulse duration [165]. In addition, the dependence between DoA and DoD remains to be studied once it can be correlated [166]. Also, the clustering phenomenon at THz frequencies must be treated carefully, given its dependence on reflection and scattering properties. To study the performance of IS in a more realistic scenario, with the complexity and amount of environmental information of THz channels, accurate modeling for both the IS element and the IS channel, is needed [156; 165; 162]. For channel modeling, when an IS is included, extensive work has been conducted to develop a sufficiently accurate model with acceptable complexity. Additionally, real-time optimization of IS phase-matrix is necessary to enhance the overall system performance [167]. With a massive number of reflecting unit elements to compensate for the severe propagation losses, existing methods of THz communication channel modeling, offset by intelligent signal processing algorithms and wireless connectivity techniques, require high-performance computing [168]. The idea is to apply machine learning tools and AI methods with affordable computational complexity to facilitate the reconfiguration of the IS phase matrix [169]. A THz wireless communication system based on the IS can be a secure communication method because it needs to know the mapping relationship between the received signal and the IS to reflect the transmitted information properly. The chip-scale communication also deserves special attention regarding further investigation of IS application. As pointed out in [133; 152], it is possible to conduct a more in-depth analysis of intricate scenarios, such as the ones involving one transmitter and multiple receivers. The analysis of WiNoC can also be improved by incorporating different wave processing in scattering enclosures like matrix multiplication, signal differentiation, and reservoir computing [170; 171; 172].