# Investigating and Modeling of Cooperative Vehicle-to-Vehicle Safety Stopping Distance
## 5 Simulation of Field Tests
### Analysis of Distance-Based Results  
The results from our experiments show that the usage of communication can assist with the reduction of stopping distance, enabling a reduction of up to 30% when packet losses are 0. However, for the consecutive losses, we can see an impact in both distance dependent and distance independent cases.  
Our results show that, at all speeds, consecutive packet loss leads to a reduction in stopping distance. We can also see how important data rate is for vehicle communication, as at each instance of 10 pps for 30 and 50 mph shown in Figures 4 and 5, a negative value is produced indicating the stopping distance has reduced below 0. This means the following vehicle has either collided with the lead vehicle or overtaken it.  
Figure 4 shows the results for 30 mph and shows the data rates of 120 and 140 pps have a reduction of less than 5 m, which is the average length of a vehicle, hence leaving two vehicles space still available to take emergency action. When considering the maximum consecutive packet loss, the minimum data rate that would provide adequate time to respond would be above 75 pps per second in the 50 mph experiments, as seen in Figure 5. Anything lower than this and the stopping distance is reduced by between 50-75%. In the 70 mph example in Figure 6, 25 pps would have a reduction of less than 40%, and the higher data rates with consecutive loss degrade the stopping distance by approximately 10%.  
We can draw a conclusion from our results that, at lower speeds, the consecutive packet loss has much more of an impact. This is due to the stopping distance being smaller, therefore giving less distance to receive the delayed communication message. However, due to high speeds, if packets are not sent at a high enough rate the stopping distance is reduced too low for adequate reaction. This leads to less time for an action to be made, but we also show that this can be mitigated with high data rates.  
The main conclusion to be drawn from the distance dependent test is that, in order to mitigate the effects of consecutive losses, high data rates must be used in order to provide  
Figure 11: Seventy miles per hour (112.63 km/h) distance dependent reduction in stopping distance.  
Figure 10: Fifty miles per hour (80.45 km/h) distance dependent reduction in stopping distance.  
adequate reaction time. We can also see that, if the requirement of a 99.9% reliable system is adhered to, that, in all tests, a loss of two packets consecutively has minimum effect in Figures 9-11. We can also see that the lower data rates suffer more at higher distances but cause more significant degradation to stopping distance at lower distances; the primary example of this can be seen in the 30 mph tests in Figure 9. It can also be seen that, as the distance increases, the packet losses have less of an impact exponentially.  
Figure 7 can also show the reason that the packet loss suffers somewhat at lower distances. The figure shows received power levels at distances up to 250 m, but our focus is only to 100 m. It also shows the fading characteristics indicated at the lower distances by the rapidly changing power levels, hence having the higher losses seen at lower distances. Figure 7 also highlights the power levels for lower distances suffer fading, but 100 m has a lower power level and yet does not suffer the same level of packet losses. This can be attributed to the fading characteristics of the channel and the gain settings on the SDR; we can also see that, at 60 m, a significant level of fading is observed.