## 6 Performance Evaluation
### Evaluation for the Designed Protocol  
#### 6.1.1 Protocol Comparison Simulation Setup  
In our simulator, vehicles move along a span of a multi-lane, bi-directional highway with length \(L_{\rm road}\). The desired average overall vehicle density \(\rho\) is realized by feeding each lane with a flow of vehicles, with three lanes devoted to each direction. On each direction, lane flows have different intensities, such that the slow lane average density and the middle lane average density are three-times and two-times the density of the high speed lane, respectively. Vehicle micro-mobility is generated according to the Krauss car-following model [61; 62], with the following parameters: the maximum speed for all vehicles on the road \(v_{\rm max}=150\) km/h, the minimum distance gap between any two consecutive vehicles \(d_{\rm min}=6\) m, the braking time \(t_{\rm break}=1\) s, the correlation coefficient of driver speed \(a_{\rm csi}=0.95\), the maximum acceleration \(a_{\rm max}=1.5\) m/s\({}^{2}\) and the maximum deceleration \(b_{\rm max}=3\) m/s\({}^{2}\). The default values of the main parameters for our simulation are shown in Table 2.  
For each round of simulation, a content request is generated in one randomly-selected vehicle, which is regarded as the SUV. The target scenario for the simulation is the road surveillance service, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Description** & **Value** \\ \hline \(t_{\rm min}\) & the minimum timer & 0 ms \\ \(t_{\rm max}\) & the maximum timer & 100 ms \\ \(e\) & the parameter for the proposed LBRP & 0.5 \\ \(L_{\rm max}\) & the link lifetime threshold & 10 s \\ \(V\) & the target content size & 5 MB \\ \(P_{\rm L}\) & the transmission power & 500 mW \\ \(C\) & the data transmission rate & 3 Mbps \\ \(R\) & the radio coverage range & 558 m \\ \(d_{\rm width}\) & the width of each driving lane & 4 m \\ \(d_{\rm SD}\) & the inter-transceiver distance & 2 km \\ \(L_{\rm road}\) & the length of the considered highway span & 20 \(R_{\rm max}\) \\ \(\Delta t\) & the minimum sampling time interval & 1 s \\ \(\rho_{1}\) & the vehicle density for the high-speed lane & 10 vehicles/km \\ \(v_{\rm max}\) & the maximum speed for all vehicles on the road & 150 km/h \\ \(d_{\rm min}\) & the minimum distance gap between any two vehicles & 6 m \\ \(t_{\rm break}\) & the time needed for braking & 1 s \\ \(a_{\rm csi}\) & the correlation coefficient of driver speed & 0.95 \\ \(a_{\rm max}\) & the maximum acceleration & 1.5 m/s\({}^{2}\) \\ \(b_{\rm max}\) & the maximum deceleration & 3 m/s\({}^{2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The default values of the main parameters in our simulations. LBRP, Lifetime-aware Beacon-less Routing Protocol. where the SUV wants to get the video information of road segments \(d_{\text{SD}}\) ahead. We assume that up to three vehicles, which carry the target video content, will serve as the candidate SOVs. All of the other vehicles will serve as the candidate BVs. As it should be guaranteed that the request message can achieve at least one SOV, we define the TTL value as \(\left\lceil 2d_{\text{SD}}/R\right\rceil\). The performance of our proposed LBRP algorithm is verified with three state-of-the-art schemes:  
* Distance-Based Forwarding (DBF): the forwarding decision is based on maximizing the one-hop transmission distance, i.e., the timer used by DBF is given by Equation (7) with \(\epsilon=0\). By extending the one-hop transmission distance, DBF can reduce the number of hops of the content delivery path. This is the main target of many multi-hop dissemination scheme designs, originally proposed in [63] and analyzed in, e.g., [5,6]. The DBF is essentially coincident with the Contention-Based Forwarding (CBF), specified as an alternative mode of operation of the standardized GeoNetworking protocol in [64]. Moreover, the DBF concept can also be found in the beacon-based algorithms, e.g., the GPSR protocol [6].