## 3 Optimal Power Allocation (PA), Cooperative Relaying and Channel Models in PD-NOMA
### Cooperative Relaying and Channel Models in PD-NOMA
The K-factor (line of sight paths) is equal to 1, the path delay vector is [0 0.4 0.9], the path gain vector in dB is [0 -5 -10], and a doppler spread equal to 0.5 is chosen. For the Rayleigh fading channel,  
Figure 8: SISO cooperative relaying PD-NOMA model (U1 is used as a relay). SUI-6 parameters are used, such as K-factor equal to 0, path delay vector is [0 14 20], path gain vector in dB is [0 \(-\)10 \(-\)14], and a doppler spread equal to 0.5. In practical scenarios, the 5G micro-cell may consist of plants or foliage. This foliage drastically affects high-frequency communications, such as mm-Wave communication at GHz frequencies. The losses are proportional to the foliage depths (\(d_{f}\)) and carrier frequency. In the proposed model, we use the ITU-developed Weissberger model [44; 45], which accounts for propagation losses related to foliage. \[PL_{d_{f}}= \begin{cases}1.33f_{c}^{0.284}d_{f}^{0.588},&14m<d_{f}\leq 400m\\ 0.45f_{c}^{0.284}d_{f},&0m<d_{f}\leq 14m\\,\end{cases}  \tag{14}\]  
where \(PL_{d_{f}}\) denotes the path loss due to foliage, \(f\) denotes the frequency in GHz and \(d_{f}\) is the foliage depth. We simulate the Weissberger model at 28 GHz with different foliage depths as shown in Figure 9. As the foliage distance between the BS and the user increases, the path loss increases as well, as shown in Figure 9. So it is recommended that for larger foliage depths among the gNodeB and users, higher power will be assigned to those users. The total path losses for a user are calculated by adding NYUSIM path losses (\(\text{PL}(f_{c},d)\)) and foliage losses (\(\text{PL}_{d_{f}}\)) which is given by:  
\[\text{PL}_{total}=\text{PL}(f_{c},d)+\text{PL}_{d_{f}}. \tag{15}\]  
In the results section, we conclude from Figures 10 and 11, that incorporating the cooperative relaying technique into ordinary PD-NOMA systems improves the BER performance of U\({}_{2}\). the existing the existing DBPA algorithm from [18] for two users in the PD-NOMA system. The FIS system is then utilized to assign optimal power to each user, and the two power distribution strategies are compared in terms of performance. The bit-error-rate (BER) for each user signal is calculated using Monte Carlo simulations to determine the difference between transmitted and received bits. The BER curves at \(10^{-3}\) along the Y-axis are used to compare the results, and hence they are plotted against different SNR values. The comparison of BER curves for PD-NOMA employing DBPA and the proposed FIS-based optimal PA schemes is shown in Figure 10. The distance separation of near-user U\({}_{1}\) and far-user U\({}_{2}\) from gNodeB is \(d_{1}=60\) m and \(d_{2}=180\) m, respectively. Using the DBPA scheme, U\({}_{1}\) is allocated with \(P_{1}=0.23\) and U\({}_{2}\) with \(P_{2}=0.77\). The FIS system uses three parameters to determine optimal powers for each user: (\(d_{1}=60\) m, \(d_{f1}=10\) m and \(SNR_{1}=14\) dB) for user U\({}_{1}\) and (\(d_{2}=180\) m, \(d_{f2}=28\) m and \(SNR_{2}=10\) dB) for user U\({}_{2}\). Here, \(P_{1}=0.34\) and \(P_{2}=0.66\) are the calculated power factors for users U\({}_{1}\) and U\({}_{2}\), respectively. The FIS system ensures fairness by providing optimal powers with equity. Fairness can be seen from the obtained SNR levels at a threshold BER of \(10^{-3}\). The proposed methodology integrates D&F cooperation in addition to assigning optimal powers. Due to the D&F cooperation scheme implemented at the near-user level U\({}_{1}\) helps to enhance the performance of far-users U\({}_{2}\). Using DBPA scheme, the obtained SNR levels at a threshold BER is 10 dB for user U\({}_{1}\) and 5 dB for user U\({}_{2}\), subsequently. While using the FIS system, the obtained SNR levels are: U\({}_{1}\) at 8.8 dB; U\({}_{2}\) at 7 dB (in only PD-NOMA), and 6 dB (in D&F PD-NOMA). In the case of DBPA scheme, the difference between the obtained SNR levels is 5 dB, while it is only 2.8 dB in the FIS-based system.