# Machine Learning-Based Methods for Enhancement of UAV-NOMA and D2D Cooperative Networks
## 5 Performance Evaluation
Also, observing all the network schemes individually (i.e., NOMA-D2D, NOMA, and OMA), the proposed ANN-based PSS outperforms the other two methods for all UFBS power transmission values. This results from the ability of the ANN to recognize patterns, indicating when each method should be conducted. Furthermore, regardless of the placement method, the cooperation between the aerial and D2D networks is promoted, i.e., the NOMA-D2D method, since it achieves the maximum spectral efficiency rates compared to standalone NOMA and OMA schemes. Moreover, for all UFBS transmission power values, the MEA-DP outperforms the  
Figure 7: Spectral efficiency for the ANN-based PSS and different terrestrial D2D bandwidth values. MED-DP scheme in all three network configurations. This is justified by the explanation given in Section 4. Specifically, as the GMTs are placed randomly and uniformly in the region of interest, the probability of an outlying user appearing is very low. Consequently, in most cases, the k-means algorithm places the UFBS at such a point that it is equidistant by the users, thus improving the quality of channels gains against k-medoids. Lastly, the spectral efficiency of the ANN-based PSS applied to the standalone NOMA scheme is higher than that of MED-DP in the NOMA-D2D cooperative network scheme for \(P_{u}\) values of approximately up to 22 dBm. This phenomenon occurs due to the improvement of the A2G channels through the proposed placement scheme. Consequently, in contrast to other cooperative systems, such as satellite D2D cooperative networks [27], the success of aerial and D2D cooperative networks strongly relies on the UFBS placement procedure. Hence, an inaccurate prediction concerning UAV's position might degrade the overall network quality and lay the D2D network unnecessary. Figure 8: Sum rate for the ANN-based PSS and different terrestrial D2D bandwidth values. Figure 9: Spectral efficiency for \(B_{d}\) = 0.2 MHz and different UFBS placement schemes. Next, Figure 10 presents the sum rate for \(B_{d}\) = 0.2 MHz and different placement procedures for NOMA-D2D, NOMA, and OMA network schemes. Throughout the \(P_{u}\) range and regardless of the placement method scheme, it can be shown that the sum rate of the NOMA-D2D cooperative network is superior to that of NOMA and OMA, respectively. Similarly, as in spectral efficiency in Figure 9, the proposed ANN-based PSS outperforms the other two placement procedures for all network schemes. Moreover, it is observed that the proposed method, when applied in a NOMA scheme, can achieve higher spectral efficiency gains for the MED-DP applied in NOMA-D2D for \(P_{u}>\) 22 dBm. Therefore, in such a scenario, with the deployment of the proposed method, we could avoid D2D transmission and save the entire D2D bandwidth. Overall, the sum rate results of the NOMA-D2D cooperative scheme in all placement procedures indicate that the weak user's achievable rate can be significantly improved. This advantage results from strong users cooperating with weak users of the system through out-band D2D communication.However, the sum rate and the spectral efficiency in all network schemes are heavily contingent on the UFBS placement within the region of interest. Regarding the results in Figures 7-10, the proposed ANN-based PSS outperforms the other two methods in all network schemes and can offer terrestrial users reliable and high-quality communication. Finally, Table 6 summarizes the key characteristics of the proposed ANN-based PSS and the compared MEA-DP and MED-DP schemes. Specifically, our method is less sensitive to outliers compared to MEA-DP, making it more robust in noisy environments. It also has higher reliability compared to both MEA-DP and MED-DP. Regarding spectral efficiency and sum rate, our method outperforms both MEA-DP and MED-DP, indicating that it may be a better choice for optimizing the utilization of resources and achieving higher data transmission rates in the given scenario.