# Novel Resource Allocation Techniques for Downlink Non-Orthogonal Multiple Access Systems
## 5 Results and Discussion
### Performance Evaluation
With 20 users at the BS, the system energy efficiency of the NOMA-PDKL-HNG technique is greater than those of NOMA-DC [28], NOMA-FTPA [11] and OFDMA by 0.66, 1.44 and 5.85 times, respectively. The system energy efficiency performance versus the BS transmit power to circuit power (PBS/Pc) \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Default Value** \\ \hline Radius of the cell (\(R\)) & 500 m \\ Maximum BS transmit power (\(P_{max}\)) & 41 dBm \\ Circuit power consumption (\(P_{c}\)) & 1 W \\ System bandwidth (\(B_{w}\)) & 5 MHz \\ Noise power spectral density (\(N_{0}\)) & \(-\)174 dBm/Hz \\ Decay factor (\(\alpha\)) for FTPA & 0.4 \\ Path-loss exponent (\(\beta\)) & 2 [8] \\ Minimum data rate for strong user & 200 Kbps \\ Minimum data rate for weak user & 20 Kbps \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameter specifications [28]. Figure 3: System sum rate vs. base station (BS) power with 10 UEs. ratio is shown in Figure 6. The BS transmit power is set at 12 W and the circuit power is set at 1 W with only 10 users available at the BS [28]. The results show that the energy efficiency decreases gradually as the power ratio increases because the energy efficiency is inversely proportional to power. NOMA-PDKL-HNG achieves higher energy efficiency when the power ratio is low and decreases faster upon power ratio increment  
Figure 7 shows the effect of the varying the number of users on fairness performance. The BS transmit power is set to 41 dBm with only 10 users available at the BS [28]. In a two-user case, the NOMA-PKKT-HNG has the highest fairness compared to all other schemes. The fairness trend  
Figure 4: System sum rate vs. number of UEs per BS. Figure 5: System energy efficiency vs. number of UEs. Figure 6: System energy efficiency vs. power ratio with 10 UEs. decreases as the number of multiplexed users in the subchannel increases. With four users, the fairness of NOMA-PKKT-HNG shows better performance than NOMA-DC [28] and NOMA-FTPA [11] by 1.94%, and 8.51%, respectively. However, the fairness performance of OFDMA remains constant regardless of the variation of the number of users in the system because the power is always assigned equally between the users. Figure 8 illustrates the fairness index with BS power variation from 1 to 5 W. The BS power with 10 users is considered. In contrast to other approaches, the fairness of the NOMA-PDKL-HNG technique increases as power transmission increases. This is due to the increment of the allocated power per user, which increases their data rate and fairness. In NOMA-DC, it can be shown that fairness is unstable: the fairness is the same from 2 to 4 W and increases at 5 W. The fairness of NOMA-FTPA is slightly higher than that of conventional OFDMA, with almost the same fairness even upon the increment of transmit power. Figure 9 depicts the system energy efficiency with a different number of iterations. The system has a 1 W BS power and a maximum number of 10 UEs. It is shown that NOMA-PDKL-HNG achieves high energy efficiency at all iterations compared to other methods. This is because the pairing process is achieved with optimal pairing process, and power is assigned to the users with less complex mathematical formulation. The optimal performance for all methods is obtained immediately after the first iteration. Figure 8: Fairness vs. BS power with 10 UEs. Figure 7: Fairness vs. number of UEs.