# Coordination of Congestion and Awareness Control in Vehicular Networks
## 4 Evaluation
### Congestion, Awareness and Topology Control  
The proposed COMPASS coordination methodology offers better evolution perspectives than integrated solutions, and could be directly used within ETSI's DCC framework to coordinate congestion and awareness control functions. Another important advantage of COMPASS is that it can coordinate multiple protocols operating over the same parameters. To demonstrate this, we have also evaluated the capacity of COMPASS to coordinate congestion, awareness and topology control protocols. While the integration of the three protocols is not straightforward, their coordination using COMPASS is simple. It only requires computing the protocols' CSs and the Intersection CS (the process previously explained is maintained). The topology control protocol here implemented for illustrative purposes is an ideal scheme designed to maintain the number of neighbors above a minimum threshold in order to ensure certain network connectivity. To this aim, the topology control protocol linearly increases the minimum transmission power required until 25 vehicles are present in the neighbor table. Similarly, the transmission power is linearly decreased when more than 250 vehicles are present in the neighbor table. The transmission power is increased or decreased in 1 dB steps. The topology control protocol is hence referred to as TOWER (Topology Control through Linear Power Control). COMPASS has been applied to coordinate the congestion (A-DCC), awareness (MINT) and topology (TOWER) control protocols. Figure 9 plots  
Figure 8: Snapshot of the transmission frequency used by each vehicle after 50 s of simulation time for a traffic density of 50 veh/km/lane. (**a**) A-DCC. (**b**) MINT. (**c**) INTERN. (**d**) COMPASS. Figure 7: Snapshot of the packet transmission power used by each vehicle after 50 s of simulation time for a traffic density of 50 veh/km/lane. (**a**) A-DCC. (**b**) MINT. (**c**) INTERN. (**d**) COMPASS. the spatial distribution of the average \(CBR\), \(D_{p}\) and number of neighbors. The results are shown for different ranges of the \(CR\) requirement. The results depicted in Figure 9 show that COMPASS is capable to successfully coordinate the operation of the congestion, awareness and topology control protocols since the \(CBR\) is maintained below \(CBR_{max}\), \(D_{p}\) is higher than 0 for all vehicles, and the number of neighbor vehicles is maintained above the 25 minimum threshold. These results clearly demonstrate that COMPASS is capable to successfully coordinate different protocols that operate on the same communication parameters without modifying their implementation or having to design new integrated solutions. This section also analyzes the capacity of COMPASS to adapt its coordination process to varying context and operating conditions. The coordination of A-DCC, MINT and TOWER results in that the minimum transmission power that each vehicle requires is established by the topology or awareness control protocols (depending on the context conditions) since A-DCC is designed to utilize a fixed transmission power. In the case of the higher range of \(CR\) values (50 to 200 m), the transmission power level required by the awareness control protocol is high, and therefore the number of neighboring vehicles is also high. As a result, the minimum transmission power to be used (compliant with the ICS) is established by the awareness control process, and not by the topology control protocol. On the other hand, when we consider the lower \(CR\) range (10-50 m), the transmission power required for awareness control is lower, and the minimum required transmission power (again compliant with the ICS) is in many cases the one demanded by the topology control process. These trends are illustrated in Figure 10. This figure depicts the time evolution of the percentage of vehicles with a required minimum transmission power (i.e., minimum transmission power in the ICS) established by the awareness control protocol MINT.