# A Bandwidth-Efficient Dissemination Scheme of Non-Safety Information in Urban VANETs +
## 4 Parameter Tuning and Evaluation through Simulations
### Results
#### 4.3.1 Parameters for Broadcast Suppression
Apart from the higher traffic density, there are multiple paths that connect the source of the message to any vehicle that is in the same connected network. The access to the channel is more difficult, especially if we face collisions due to several relays forwarding at the same time. Figure 3: Simulation results of the base roadway scheme with different \(T_{max}\) values in the New York scenario: (**a**) long-reach success rate; (**b**) delivery ratio; (**c**) forwarding ratio; (**d**) number of lost packets; (**e**) average per-hop delay; (**f**) average end-to-end delay. We use the value we found above, \(T_{max}=350\) ms, in the map-based variant to study the effect of \(T_{j}\) alone. This parameter is the maximum wait for vehicles at junctions. We want vehicles at intersections to wait, at most, the same as vehicles applying the general distance-based contention equation. Thus, it must be less than or equal to \(T_{max}\). In order to better understand the simulated points, the \(x\)-axis of the graphs in Figure 4 represents the relation between \(T_{j}\) and \(T_{max}\) instead of absolute values. There, we can see that the success, be it in terms of long reach (Figure 4a) or delivery ratio (Figure 4b), is not related to this waiting time either. We also find a very limited effect in the redundancy ratio from Figure 4c. The slight rise is caused by vehicles at a junction that are also the furthest from the  
Figure 4: Results of the map-based scheme with fixed \(T_{max}\) and different \(T_{j}\) values in the New York scenario: (**a**) long-reach success rate; (**b**) delivery ratio; (**c**) forwarding ratio; (**d**) portion of relays from junctions; (**e**) number of lost packets; (**f**) average per-hop delay; (**g**) average end-to-end delay. previous relay. They wait so much that another vehicle forwards first, though it does not inhibit them. It is almost balanced out by the slightly higher number of vehicles that forward from junctions (Figure 4d) when their wait is shorter. Again, a very short maximum delay has the same problems of redundancy and losses as \(T_{max}\) did, and that we can see in Figure 4e. The average per-hop delay, shown in Figure 4f, is clearly influenced by the vehicles that have to wait less because they are at intersections. However, this effect is hidden in the average end-to-end delay, as we can appreciate in Figure 4g. Following a similar reasoning to that for \(T_{max}\), we find that \(T_{j}/T_{max}=0.6\) is the best compromise between losses and delay. This corresponds to \(T_{j}=210\) ms.  
Figure 5: Results of the angle-based scheme with fixed \(T_{max}\) and \(T_{j}\), and varying \(\Delta\alpha\) in the New York scenario: (**a**) long-reach success rate; (**b**) delivery ratio; (**c**) forwarding ratio; (**d**) portion of relays from junctions; (**e**) number of lost packets; (**f**) average per-hop delay; (**g**) average end-to-end delay. Now, we set to find out the angle thresholds, \(\alpha_{min}\) and \(\alpha_{max}\). They will let us determine if a vehicle is receiving a message from a different street, by comparing the reception angle with these two thresholds. The reception angle is calculated by using the relay's reported location and the receiver knowledge of its own trajectory. We define \(\Delta\alpha\) as the difference between \(\alpha_{max}\) and \(\alpha_{min}\). We can observe the effect of this parameter in Figure 5. When \(\Delta\alpha\) is a flat angle to either side, every reception angle indicates that the vehicle is at an intersection. Hence, all of the retransmissions are assumed to be done from intersections, because every vehicle believes it is at one. Additionally, when \(\Delta\alpha\) is \(0^{\circ}\), no one considers itself inside a junction, so none of the retransmissions is done from one. \(\Delta\alpha\) does not affect the success of the scheme, as we can see in the graphs that represent the long-reach success (Figure 5a) and the delivery ratio (Figure 5b).