# A Bandwidth-Efficient Dissemination Scheme of Non-Safety Information in Urban VANETs +
## 4 Parameter Tuning and Evaluation through Simulations
### Results
#### 4.3.4 Comparison with UV-CAST  
We compare the roadway scheme and the map-based urban scheme, together with the store-carry-forward mechanism for cities, with a well-known work from the state of the art, UV-CAST [3]. It is a version of DV-CAST [7] adapted to urban environments. It is intended to work in either well-connected or disconnected vehicular networks without help from fixed infrastructure. From the received beacons, a vehicle can determine if it is inside a connected region or not according to the angles to all of its neighbors. If it is, it will act according to the well-connected regime, applying a broadcast suppression scheme. It consists of a distance-based contention to forward the message first. The waiting time for vehicle \(i\), \(\tau_{i}\), is calculated using Equation (6):  
\[\tau_{i}=\begin{cases}\frac{1}{2}\left(1-\frac{d_{i,j}}{\mathcal{R}}\right) \tau_{max}&\text{ if $i$ is at an intersection}\\ \frac{1}{2}\left(2-\frac{d_{i,j}}{\mathcal{R}}\right)\tau_{max}&\text{ if $i$ otherwise}\end{cases} \tag{6}\]  
where \(d_{i,j}\) is the distance from the relay, vehicle \(j\), \(R\) is the maximum transmission range and \(\tau_{max}\) is the maximum waiting time. It follows that vehicles that are located at intersections wait half of the maximum wait at most. The authors do not clarify how the vehicle gets knowledge about intersections, but we could assume it gets the information from a digital map. At the end of the wait, if it did not receive any new duplicate, it forwards the message and inhibits the rest. Then, all of the participants become idle again.  
If it is a boundary node or a totally disconnected node, it will enter the disconnected regime and store-carry-forward the message. Whenever it receives a new beacon, it forwards the stored message. This is repeated until it exits the area of interest associated with the message.  
In the evaluation by the authors, its parameter \(\tau_{max}=500\) ms. We modify it to \(\tau_{max}=350\) ms, to match our \(T_{max}\) value.  
The graphs in Figures 16-18 show the performance results of our simulations. According to the graphs showing the involved vehicles (Figure 16a,b), we can see that UV-CAST reaches a low number of vehicles in the first stage of the dissemination. However, it achieves an almost total coverage in the long run, even in low traffic densities. Our solutions, on the other hand, get to a higher number of vehicles in the first few seconds, especially in high densities, but the increase over time is limited. The cause of UV-CAST's high coverage is its overhead, as we can verify in Figure 17a,b. We can see that the vast majority of duplicates when using UV-CAST are due to its store-carry-forward mechanism. This is what lets the protocol reach such a high number of targets.  
Finally, the ratio graphs in Figure 18a,b summarize what we have just observed. Our alternatives' ratios grow together and slowly towards the one duplicate per receiver reference. UV-CAST, for its part, starts with a low ratio, which justifies the low coverage in the early dissemination stage, and rises  
Figure 16: Involved vehicles in comparison with UV-CAST in the New York scenario: (a) 25 vehicles/km\({}^{2}\); (b) 100 vehicles/km\({}^{2}\).  
Figure 17: Sent duplicates in comparison with UV-CAST in the New York scenario: (a) 25 vehicles/km\({}^{2}\); (b) 100 vehicles/km\({}^{2}\).  
fast to several duplicates per receiver. It is significant that it causes relatively more overhead as the density is higher, as opposed to our schemes.