# Machine Learning-Based Methods for Enhancement of UAV-NOMA and D2D Cooperative Networks
## 5 Performance Evaluation  
In this section, the system sum rate and the spectral efficiency results from Monte Carlo simulations conducted in Matlab(r) are presented to evaluate the performance of the proposed ANN-based PSS. The simulations were executed on a computer consisting of a Windows 10 64-bit operating system, Intel Core i7-8700 CPU, and 16 GB of RAM. Moreover, the impact of various system parameters, such as D2D bandwidth allocation and the UFBS transmit power \(P_{u}\), on the performance of the proposed method is studied. Furthermore, the proposed ANN-based PSS is compared against the standalone UFBS placement schemes k-medoids and k-means [7; 9]. These two methods will be referred to as the k-means deployment process (MEA-DP) and the k-medoids deployment process (MED-DP). More specifically, comparisons are made between different networks schemes, such as the cooperative UAV-NOMA and D2D scheme termed as NOMA-D2D, and two standalone UAV transmission schemes without D2D communication capabilities between the GMTs, the UAV-NOMA optimal user pairing scheme [26], called NOMA, and the time domain UAV-OMA scheme, termed as OMA. In order to assess the performance of the proposed scheme as well as the compared ones, we define the spectral efficiency as:  
\[SE=\frac{R_{ach}}{B_{occ}}, \tag{38}\]  
Figure 5: Accuracy comparison between the different ANN layouts. Figure 6: F1-score, precision, and recall performance measurements of all ANN layouts. where \(R_{ach}\) is the achievable system sum rate and \(B_{occ}\) denotes the total utilized network bandwidth. Concerning both the standalone OMA and NOMA transmission scheme, \(B_{occ}=B_{u}\), while for the NOMA-D2D scheme, \(B_{occ}=B_{d}+B_{u}\). The rest of the selected parameters regarding the abovementioned scenarios are listed in Table 5.  
Figure 7 presents the spectral efficiency performance of the proposed ANN-based PSS for different terrestrial D2D bandwidth values and between the different network schemes. As it can be observed, the proposed ANN-based PSS scheme combined with the NOMA-D2D transmission technique for \(B_{d}=0.2\) provides significant spectral efficiency gains compared to the other NOMA-D2D cooperative networks with \(B_{d}\
eq 0.2\) and the standalone NOMA and OMA schemes. It is noteworthy that the proposed strategy, utilizing a \(B_{d}\) equal to 0.1 MHz, exhibits comparable performance with a \(B_{d}\) equals to 0.2 MHz for low UFBS transmit power values. Conversely, for high UFBS transmit power, the proposed strategy utilizing a \(B_{d}\) equals to 0.2 MHz is determined to result in the near optimal spectral efficiency. Also, regarding the NOMA-D2D cooperative network with \(B_{d}\leq 1.2\) MHz, the proposed method achieves higher spectral efficiency gain than the standalone NOMA and the OMA scheme for all UFBS power transmission values. In contrast, for \(B_{d}>1.2\) MHz, the suggested method's spectral efficiency in a NOMA-D2D cooperative network is inferior to that of NOMA. This occurs because there is no need for additional bandwidth since the weak users' rates are always constrained by the decoding rates of their signals at the strong users (21). Therefore, regarding the communication network, \(B_{d}\) values greater than 1.2 MHz are considered a waste of resources. Additionally, for \(B_{d}=1.2\) MHz, a switch case statement can be established. More specifically, in the case where the \(P_{u}\) is lower than 20 dBm, the NOMA-D2D cooperative network outperforms the NOMA scheme, while for \(P_{u}>20\) dBm, the standalone NOMA outperforms the NOMA-D2D cooperative scheme. This phenomenon occurs for large \(P_{u}\) values since the A2G channel between the weak GMTs and the UFBS is strengthened, resulting in greater achievable rates for the weak GMTs via the direct A2G connection. Hence the D2D communication between the K pairs is mainly avoided, as the offered data rates via the D2D links are lower than those that can arise through the A2G links. This claim can be verified by expression in (21).