# Multiple-Intelligent Reflective Surfaces (Multi-IRSs)-Based NOMA System
## 5 Simulation and Numerical Results
### Numerical Results of a Single-Reflection Surface Scenario  
Figure 3 illustrates a comparison between IRS-NOMA and IRS-OMA in terms of the required number of reflective elements \(N\) against the achievable EE, with both system being required to maintain a specified level of the target rate. It is worth mentioning that the expression of EE is  
\[EE=B\frac{SE}{P_{Tot-cons}}. \tag{14}\]  
The performance is examined at high \(N\) values to surveillance the behaviors of both systems in such a situation. This figure depicts that IRS-NOMA achieves the same EE as IRS-OMA, but with much less reflective elements; for instance, it could be observed that at \(N=300\), IRS-NOMA achieves approximately double EE than that achieved by IRS-OMA. This proves that IRS-NOMA is less complex and more cost effective than IRS-OMA, and this figure shows that IRS-NOMA outperforms IRS-OMA at high levels of \(N\). Despite the fact that IRS-NOMA offers better outcomes than IRS-OMA, Figure 3 shows that EE trends in general are declining for both systems, which reflects the fact that higher \(N\) levels lead to more power consumption and more non-useful wave scattering, which causes power wastage, and therefore is non-energy efficient. It is worth mentioning that, from Figure 3, the EE decreases continuously as \(N\) increases; however, this merely extends to a certain level, and then EE starts to reach a steady state where increasing \(N\) is not effective. To test the IRS-NOMA and IRS-OMA abilities to achieve given target rates, Figures 4 and 5, respectively, show the required transmission power by both systems to reach a predetermined target rate, and at the same time, maintain successful transmission over a given distance between the source and the destination. To examine the effects of all the respective variables, the two figures considered three different \(N\) scenarios: 50, 100, and 180, besides varying the target rate between 50 Mbit/s and 100 Mbit/s, over \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter Name** & **Value** \\ \hline Total number of active users (\(U\)) & 3 \\ \hline Carrier frequency (\(f_{c}\)) & 5 GHz \\ \hline Overall transmission bandwidth (\(B\)) & 10 MHz \\ \hline The standard deviation of shadowing & 8 dB \\ \hline the total transmission power (\(P\)) & 40 dBm \\ \hline Dissipated power by each reflective element (\(P_{E}\)) & 5 mW \\ \hline Dissipated power by the source (\(P_{\text{S}}\)) & 20 dBm \\ \hline Dissipated power by the destination (\(P_{D}\)) & 100 mW \\ \hline Dissipated power by the rely (\(P_{R}\)) & 100 mW \\ \hline Noise power spectral density (\(\sigma^{2}\)) & \(-174\ dBm/\Hz\) \\ \hline \(\beta_{SR}=-28-20*log10(f_{c})-22*log10(d_{SR})+G_{S}+G_{R}\) & 3 GPP LOS path-loss \\ \hline \(\beta_{RD}=-28-20*log10(f_{c})-22*log10(d_{RD})+G_{R}+G_{D}\) & 3 GPP LOS path-loss \\ \hline \(\beta_{SD}=-22.7-26*log10(f_{c})-36.7*log10(d_{SD})+G_{S}+G_{D}\) & 3 GPP NLOS path-loss \\ \hline Noise figure & 10 dB \\ \hline The reflection coefficient (\(\alpha\)) & 1 \\ \hline Transmitting antenna gain (\(G_{S}\)) & 5 dB \\ \hline Receiving antenna gain (\(G_{R}\)) & 5 dB \\ \hline Transmitting antenna gain (\(G_{D}\)) & 1 dB \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation Setup. several \(d\) measurements. It is worth mentioning that the achievable target rate for the users of both systems is affected by several factors such as the available transmission power allocated to each user and the channel conditions of each user. Increasing the distance or placing the destinations at farther locations will degrade the performance to a point where the users with bad channel conditions will need more transmission power to achieve a given target rate. It can be concluded from both of these figures that IRS-NOMA requires less power than its orthogonal peer. This proves and confirms that IRS-NOMA requires less transmission power, and hence, is more energy efficient than IRS-OMA for various destination locations.