# User-Information-Aware D2D Multicast File Distribution Mechanism
## 7 Simulation Analysis
### Effects of Various \(\left|U_{p}\right|\) on Utility of the Proposed Scheme  
Obviously, the number of the potential service requesters is a key factor influencing the performance of user-information-aware D2D multicast file distribution mechanism. To explore the relationship between the performance of the proposed mechanism and its own parameter settings, the performances in different communication environment of the proposed mechanism with different number of potential service requesters are studied in this section. As shown in Figure 4, by sequentially changing the weight of video's popularity \(\lambda\), the willingness threshold to accept video push service \(p_{th}^{accept}\) and the number of files \(\left|F\right|\), the performance of D2D multicast file distribution system with different number of potential service requesters shows a huge difference. In general, the utility value of a D2D multicast system is proportional to the number of potential servicing users \(\left|U_{p}\right|\), where the value of D2D multicast utility metric reflects the average throughput of the D2D multicast file distribution system. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Values** \\ \hline The maximum distance (D2D) & 60 m \\ Channel bandwidth \(B\) & 180 KHz \\ Path loss exponent \(\alpha\) & 4 \\ Noise spectral density & \(-\)174 dBm/Hz \\ The circuit loss constant \(E_{dec}\) & 50 nJ/bit \\ Cluster head transmit power \(P_{h}\) & 23 dBm \\ Cellular user transmit power \(P_{c}\) & 30 dBm \\ The willingness threshold \(p_{th}^{accept}\) & 0.5 \\ The number of service requesters \(\left|U_{R}\right|\) & 20 \\ The number of potential service requesters \(\left|U_{p}\right|\) & 10 \\ The number of videos \(\left|F\right|\) & 5 \\ The weight of video popularity \(\lambda\) & 0.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. As shown in the Figure 4a, with the rise of the value of \(\lambda\), the value of utility increases firstly and then decreases and the more potential service requesters, the faster the value of utility drops. That is because the increase in the value of \(\lambda\) makes that the video popularity \(P_{l}^{pop}\) has greater weight in calculating the user's request probability, further reducing the difference of video request probability among users and increasing the intensity of social relationships, thereby the value of utility increases. Nevertheless, when the video popularity \(P_{l}^{pop}\) is a constant, the excessive value \(\lambda\) will cause the smaller absolute value of the willingness \(P_{pi,l}^{accept}\) so the number of potential service requesters who can meet the condition \(P_{pi,l}^{accept}>P_{th}^{accept}\) will decrease, leading to a decrease of utility value and the greater number of potential service requesters, the greater it decreases. As can be seen from Figure 4a, the utility value of the four curves can reach a maximum when the value of the \(\lambda\) belongs to the interval [0.4, 0.7], so we set the value of lambda in other experiments to 0.6. As shown in Figure 4b, when the value of the user's willingness threshold \(P_{th}^{accept}\) continues to rise, the four curves all show a sharp downward trend until the willingness threshold is 0.7, and the greater number of potential service requesters, the greater the decline. That is because that, for any potential service requester in the D2D multicast cluster, the willingness to accept the pushed video file \(f_{l}\in F\) must greater than the willingness threshold \(P_{th}^{accept}\). If the value of \(P_{th}^{accept}\) rises, the number of users meeting the conditions will decline, and the performance of utility will decrease dramatically. The simulations reveal that the value of the willingness \(P_{pi,l}^{accept}\) for most of the potential service requesters is less than 0.7.