## 5 Performance Evaluation
### Tuning of the Multihop P2 MP Settings
#### 5.1.1 Varying Application-Level Settings  
In this subsection, we evaluate how different settings of the UE's application layer affect the performance of the broadcasting and compare MDB with the relaying made by the eNB. We assume that the eNB uses the SRA allocation policy, using the scheduling algorithm described in [32], where two or more UEs can reuse the same RBs if they are not interfering each other. In particular, interference conditions are modeled through a conflict graph [38], which is maintained by the eNBs according to UEs' location information. In the conflict graph, two UEs are conflicting if the power they receive from each other is above a threshold of \(-50\) dBm. In that case, the UEs are placed on different RBs, otherwise they can share the same RBs. Figure 9 shows which UEs receive a broadcast message, when either TTL or GPS coordinates and radius are used. The UE marked with the cross is the one that originates the message, and the boundary of the target area (i.e., the shaded one) is marked by the vertical dashed line. Note that the line only looks straight because the scale on the \(y\)-axis is stretched. UEs that received the message are shown as green circles, whereas red triangles represent UEs that did not. Using coordinates and radius (top left of Figure 9) allows the message to reach all the desired UEs, and few of those outside the range. When TTL is used, the set of UEs depends on the initial TTL value. If the value is set to 5 or 6, some UEs at the border do not receive the message, whereas setting it to 7 covers the entire target area. However, if the line is moved in either direction, or the UE density or the network MCS change, that value stops being optimal and must be recomputed. In order to exemplify the dissemination process of the message, Figure 10 shows the per-TTI allocation of RBs at the eNBs involved in the broadcasting process, which is started by a UE served by eNB1. Thus, the latter allocates RBs to UEs under its control to let them relay the message. After some time, the message reaches UEs served by eNB2 and eNB3, which in turn start granting transmission resources to them. eNB4 and eNB5 do not allocate RBs, since their served UEs are outside the target area. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Carrier frequency & 2 GHz \\ Bandwidth & 10 MHz (50 RBs) \\ Fading model & Jakes \\ Path loss model & ITU Urban Macro [37] \\ Noise figure & 5 dB \\ Cable loss & 2 dB \\ eNB Transmission Power & 46 dBm \\ UE Transmission Power-UL & 30 dBm \\ UE Transmission Power-D2D & 15 dBm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Physical-layer parameters. ITU: International Telecommunication Union; eNB: eNodeB; UE: User Equipment; UL: uplink; D2D: device-to-device. Figure 8: Evaluation scenario. We now evaluate the impact of the Trickle suppression mechanism on MDB. In particular, we consider different settings for its relevant parameters \(K\) and \(I\). We recall that a UE relays a message if fewer than \(K\) duplicates are received within a time randomly selected in the range \([I/2,I)\), \(I\) being the Trickle interval. Defining \(S\) as the number of transmissions performed by all UEs in the floorplan to relay a single broadcast, Figure 11 shows \(E[S]\), whereas Figure 12 reports the 95 th percentile of the time required to complete the dissemination, computed as \(t_{e}-t_{0}\), where \(t_{0}\) is the time at which the originating UEs starts the broadcast, and \(t_{e}\) is the time at which none of the UEs that have  
Figure 10: RB (Resource Block) allocation at different eNBs over time. Figure 9: Target area vs. TTL. received the message can forward it anymore (either because they already have, or because Trickle suppressed relaying). We observe that the combination of large values of \(I\) and small values of \(K\) allows us to transmit fewer messages, hence saving in terms of radio resources and power at the UEs.