## 2 Challenges and Routing in 6G Networks
### Challenges of Routing
#### 2.1.1 The Complex Structure of 6G  
The aim is to develop new structures and approaches that will contribute to the complexity of the system in 6G and next-generation networks. Below, the most significant versions are demonstrated. Figure 3: Key challenges of routing in 6G mobile networks. **THZ levels**  
It is aimed that the data transfer capacity in 6G networks will be more than 20 Gbps per second. Spectrum and energy efficiency are projected to be 3 times and 10 times higher than the previous generation, respectively. In the 6G era, goals such as high data rates, spectra, and energy efficiency require the successful implementation of the THz radio communication spectrum [35; 36]. Ultimate extreme connectivity will be possible thanks to the THz spectrum, which will play an active role in 6G. The higher the data rate, the wider the bandwidth in the THz spectrum. The 230 GHz spectrum is assigned to mobile services in the 100-450 GHz THz bandwidth range [37]. Thanks to this notable feature, it makes it possible to reach high data rates in certain distance ranges. The wide bandwidth and short wavelengths of the THz spectrum provide high resolution. This potential will take sensitive and high perception to a more advanced level in the future. The development of sensitivity and high detection will contribute to location determination and imaging systems. The 6G world has the potential to become \"a new door\" that opens to the physical, virtual, biological, and cyber worlds supported by \"sensing-supported communication\" [37]. It will also support real-time detection and digital twin technology to achieve a major breakthrough. Achieving the targeted high data rates makes the use of the THz spectrum band inevitable. In addition to its potential to provide high data rates, the THz spectrum band also increases the difficulties of communication. High frequencies between 0.1 THz and 10 THz are used in the THz spectrum. The use of these high frequencies leads to high path loss [38; 39; 40; 41; 42]. One of the biggest challenges for the THz band is the excess of the free space path loss. To compensate for this challenge, beamforming technology will be needed, which will be even easier and more effective with the support of sensitive and high detection [37]. Otherwise, the area that will benefit from the potential of THz technology will have to narrow. In addition, the THz band is a challenge in interacting with gases in the atmosphere. Since the 6G THz ranges are short, there is power loss between the antennas, the receiver, and the transmitter. This makes it difficult to produce a stable signal at ultra-wide band frequencies. In studies on this subject, a power amplifier is being developed to make it easier to produce a stable signal [43]. In addition to the propagation-related challenges, another critical barrier in the implementation of THz communication is the fabrication of antennas and components that can efficiently operate at such high frequencies [44]. As the THz band demands extremely small wavelengths, the design and manufacturing of compact, high-precision antennas become increasingly complex. Material limitations, thermal stability, and fabrication tolerances at the nanoscale significantly impact performance, reliability, and cost [44]. Moreover, the development of THz components, such as mixers, modulators, and detectors, is still in its infancy compared to microwave and millimeter-wave technologies. These hardware limitations remain major obstacles to the large-scale deployment of THz systems, necessitating continued advancements in nanotechnology, microfabrication techniques, and novel materials suitable for THz frequencies. **VLC**  
VLC is one of the potential technologies for use in order to achieve the targeted outputs. VLC uses the visible spectrum. The benefits of VLC technology are a license-free 400-800 THz spectrum range, very high spectrum reuse, ultra-high bandwidths, low cost, and zero electromagnetic interference [45; 46; 47; 48].