## 3 Materials and Methods
### Interference and Network Optimization Difficulties
#### 3.9.1 Interference  
One of the issues highlighted by the development of 5G is interference. It should be remembered that interference, by definition, is when two electromagnetic waves overlap. This overlapping causes communication failures from where the wave is sent to where it is received. There are two types of interference: constructive and destructive. Constructive interference occurs when the waves overlap or collide in phase, and this causes the resulting wave to have a greater amplitude. Furthermore, destructive interference is when there is an out-of-phase overlap, where the resultant of this wave will be of lower amplitude [80]. Some networks may be more susceptible to interference depending on the type of wave they handle, i.e., the frequency used in the electromagnetic spectrum. RF can give this interference, whereas in 5G networks, millimeter bands and below 6 GHz bands are used. In addition, it must be taken into account that these interferences will continue to grow with the development of technology. Figure 9 covers various types of interference in wireless communication systems in 5G. Adjacent channel interference occurs when adjacent frequencies or channels overlap due to imperfections in filters or non-linearity in amplifiers. Inter-cell interference happens when two users from neighboring cells try to use the same frequency band simultaneously due to resource limitation within the network. Intra-channel and inter-channel interference occur due to physical proximity of devices and low power within the macro-cell network, respectively. Inter-symbol interference results from signal distortion due to phase or amplitude dispersion in the channel. Inter-carrier occurs due to frequency offsets between sub-carriers. Inter-numerology interference arises due to non-orthogonality in the system, causing difficulties for symbol alignment. Cross-link interference occurs when signals are transmitted to neighboring cells in different directions simultaneously. Inter-beam interference happens due to the use of multi-beam antenna systems, causing interference from adjacent beams. Multi-user interference happens when several users try to transmit their information requests at the same time, and MU-MIMO is used to increase the capacity and performance of wireless broadcasting systems. We must consider that with the evolution of higher data rates, we are looking for the implementation in a frequency spectrum that is becoming more saturated daily. The development in these frequencies makes the operator reuse the same frequencies for neighboring cells to save spectrum. This development causes high interference between cells [81]. In addition to these, other interferences also occur within the networks. The classification of these interferences is as follows:  
* Adjacent channel interference: Adjacent channel interference is a problem that occurs in many devices and many frequency ranges. This occurs when an adjacent frequency or the adjacent channel of the one used by our device overlaps. This problem occurs in 5G, as in other mobile technologies. This type of interference is mainly caused, as stated in [82], by an imperfection in the filters, where they cannot filter the desired signal correctly. These imperfections result in nearby frequencies passing into the passband. In turn, this occurs because the amplifiers are not linear. * Intra-cell and inter-cell interference: Inter-cell interference is one of the most significant causes of network performance degradation. This occurs when two users from neighboring cells attempt to use the same frequency band simultaneously. This occurs,