## 5 Proposed Scheme
### Simulation Results and Discussion
#### 6.2.1 Discussion on Performance of D2D Communications  
Here, we analyze the performance of D2D communications underlaying uplink cellular networks.  
Figure 2 depicts the outage probability distribution of D2D communications at varying distance from the eNB to D2D-Rx. As expected, the D2D outage probability of the proposed scheme is much lower compared to the RRA scheme because a definite interference level is maintained. As can be seen, the outage probability increases due to the increase of uplink interference. In the RA with RF = 1 scheme, increasing the distance between D2D-Rx and eNB increases the outage probability significantly. It is observed that the analytical calculation of outage probability results of D2D is very close to the Monte Carlo simulation.  
\begin{table}
\begin{tabular}{l l} \hline \hline
**Simulation Parameters** & **Values** \\ \hline Cell outline & Hexagonal cell framework \\ Total number of resource blocks & 50 [26] \\ Cellular user transmission power & 20 dBm \\ D2D transmission power & 15 dBm \\ Antenna type & 3–120\({}^{\circ}\) directional antennas \\ Noise Power & \(-\)174 dBm/Hz \\ D2D pair distance & 1–50 m \\ Minimum device distance from eNB & 10 m \\ Carrier frequency & 2 GHz \\ Uplink bandwidth & 10 MHz [26] \\ Path loss exponent & 3 \\ Cell radius & 600 m \\ Monte Carlo simulation runs & 15,000 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Simulation parameters and values.  
Figure 2: D2D outage probability with varying distance from eNB to D2D-Rx.  
Figure 3 depicts the outage probability distribution at varying SINR threshold value. We can see from Figure that the D2D outage probability increases with the increase of threshold value of SINR. A significant lower outage probability is observed at the SINR threshold value of \(-10\) dB. It is observed that the proposed scheme experiences much lower outage probability than existing schemes. Comparing to the existing schemes, resource allocation and power control scheme with FRF of 2 yields a 20% reduction in outage probability. This is because of the fact that D2D-Tx in the proposed scheme maintains upper and lower bounds transmit power. We notice that the analytical calculation result is very close to that from the simulation result.  
Figure 4 presents the D2D throughput at varying number of available D2D pairs in a cell. We can see from the Figure that the throughput increases with the increase of D2D pairs. Our proposed scheme yields highest throughput as compared with other existing schemes. This is because of the fact that the proposed scheme dramatically reduced the outage probability. By using our proposed scheme, data traffic through the cellular users is control; hence it maximizes the success rate of transmission. Enabling D2D communications with cellular resource RF of 2 achieves a 4.43 gain in the D2D throughput as compared with RRA scheme. Moreover, our proposed scheme yields a 1.5 gain in the D2D throughput as compared with RA with FRF of 1.  
Figure 4: D2D throughput with varying number of available D2D pairs.  
Figure 3: D2D outage probability with varying signal-to-interference-plus-noise ratio (SINR) threshold.