# Machine Learning-Based Methods for Enhancement of UAV-NOMA and D2D Cooperative Networks
## 2 System Model
### Power Allocation Strategy  
Concerning the UFBS NOMA transmission, the objective is to maximize the sum rate of each pair of GMTs under the condition that both GMTs enjoy at least the rate utilizing the conventional UFBS OMA transmission. This is an optimization problem which is mathematically expressed as follows:  
\[\begin{split}\max_{\alpha_{i}}& R_{i}^{u}+R_{j}^{u},\\ \text{s.t.}& R_{i}^{u}\geq R_{i}^{o},\\ & R_{j}^{u}\geq R_{j}^{o},\\ & 0\leq\alpha_{i}\leq 1.\end{split} \tag{26}\]  
The solution to this problem has been obtained in [26; 27] by identifying the optimal value of \(\alpha_{i}\), as:  
\[\alpha_{i}=\frac{\sqrt{1+\Gamma_{j}^{u}P_{u}}-1}{\Gamma_{j}^{u}P_{u}}. \tag{27}\]  
To conclude, in Table 1, the definitions of most of the parameters involved in this study are included.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Definition** \\ \hline \(A\) & Circle region of interest \\ \hline \(u_{l}\) & 3D location of each GMT\({}_{l}\) \\ \hline \(p_{1}\) & 3D location of UFBS \\ \hline \(N\) & Total number of GMTs \\ \hline \(K\) & Total number of GMT pairs \\ \hline \(G_{t}^{u}\) & UFBS transmit antenna gain \\ \hline \(B_{u}\) & UFBS bandwidth. \\ \hline \(P_{u}\) & UFBS transmit power \\ \hline \(F_{u}\) & UFBS operating frequency \\ \hline \(B_{d}\) & D2D bandwidth \\ \hline \(P_{d}\) & D2D transmit power \\ \hline \(F_{d}\) & D2D operating frequency \\ \hline \(G_{t}^{d}\) & D2D transmit antenna gain \\ \hline \(G_{r}^{d}\) & D2D receive antenna gain \\ \hline \(N_{u}\) & A2G receivers noise power \\ \hline \(N_{d}\) & D2D receivers noise power \\ \hline \(\text{PL}_{l}^{u}\) & A2G path loss for each GMT\({}_{l}\) (\(1\leq l\leq N\)) \\ \hline \(\text{PL}_{k}^{d}\) & D2D path loss for each k pair of users (\(1\leq k\leq K\)) \\ \hline \(x_{k}^{u}\) & Superimposed NOMA signal of each k pair\(\sim\)(1 k K) \\ \hline \(\alpha_{i}\) & Power allocation factor of the strong GMT\({}_{i}\) \\ \hline \(\Gamma_{I}^{u}\) & A2G channel gain for each GMT\({}_{l}\) (\(1\leq l\leq N\)) \\ \hline \(y_{i}^{u}\) & The received signal by the strong GMT\({}_{i}\) from the UFBS \\ \hline \(y_{j}^{u}\) & The received signal by the weak GMT\({}_{j}\) from the UFBS \\ \hline \(y_{j}^{d}\) & The received signal by the weak GMT\({}_{j}\) from his pair’s strong GMT\({}_{i}\) when the D2D cooperative transmission is activated. \\ \hline \(\tau_{i}^{u}\) & SNR of the A2G link of the strong GMT\({}_{i}\) assuming perfect SIC \\ \hline \(\tau_{k}^{u}\) & SINR of the A2G link of the strong GMT\({}_{i}\) for detecting the signal \(s_{j}\) from his pair’s weak GMT\({}_{j}\) \\ \hline \(\tau_{j}^{u}\) & SINR of the A2G link of the strong GMT\({}_{i}\) for detecting its own signal \\ \hline \(\gamma_{k}^{d}\) & SINR of the D2D link of the weak GMT\({}_{j}\) for detecting its own signal, which is relayed by his pair’s strong GMT\({}_{i}\) \\ \hline \(\Phi_{k}\) & D2D channel gain for the weak GMT\({}_{j}\) when the D2D cooperative transmission is activated \\ \hline \(R_{i}^{u}\) & Maximum downlink NOMA achievable rate which succeed by the strong GMT\({}_{i}\) through the A2G channel \\ \hline \(R_{j}^{u}\) & Maximum downlink NOMA achievable rate which succeed by the weak GMT\({}_{j}\) through the A2G channel \\ \hline \(R_{k}^{u}\) & Maximum downlink NOMA achievable rate of the weak GMT\({}_{j}\)’s signal which succeed by his pair’s strong GMT\({}_{i}\) through the A2G channel \\ \hline \(R_{k}^{d}\) & Maximum achievable rate which succeed by the weak GMT\({}_{j}\) through the D2D channel \\ \hline \hline \end{tabular}
\end{table}
Table 1: System model parameters definition.