# Data Rate Selection Strategies for Periodic Transmission of Safety Messages in VANET
## 4 Simulation Results
### Comparison of Received Packets  
Figure 5 shows the total number of packets received with different constant bitrates and the DRCC approach. For low congestion scenarios, such as with a packet size of 256 bytes and a beacon interval of 0.1 s, the packet reception is better with lower bitrates of 3 or 6 Mbps. The performances of both versions of DRCC (DRCC1 and DRCC5) are very close to the best results, while higher bitrates of 18 or 24 Mbps show a significant decrease in received packets. On the other hand, bitrates of 9 or 18 Mbps perform better for very high congestion, such as with a packet size of 1024 bytes and a beacon interval of 0.05 s. In this case, DRCC5 is very close to the highest value, while the performance of DRCC1 is slightly lower, and the performance with a constant bitrate of 3 Mbps is the worst. These results indicate the advantages of using an adaptive congestion control technique, such as DRCC, over constant bitrates, since the channel load can vary widely over time. Figure 4: Comparison of CBR with DRCC vs. existing approaches. Figure 3: Comparison of CBR with DRCC vs. using constant bitrates. Next, we compare the proposed DRCC approach with two other existing data rate control approaches: data rate-decentralized congestion control (DR-DCC) [58] and transmission data rate control (TDRC) [57]. Figure 6 compares the total number of BSMs received under different channel loads, using DRCC1, DRCC5, DR-DCC, and TDRC. Under low loads, the performances of the first three approaches were very similar, while TDRC received significantly fewer packets. For medium and high loads, DRCC5 and DR-DCC were similar, with DRCC5 performing slightly better and receiving 4-5% more packets compared to DR-DCC. The performance of DRCC1 was somewhat lower, and TDRC had the worst performance in all cases except for one (with a packet size of 256 bytes and a beacon interval of 0.05 s). In general, we can see that for most approaches, the total number of received packets increases as beacon interval decreases (which is expected) under low/moderate loads. It is also interesting to note that for higher loads (with 1024-byte packets), reducing beacon interval does not increase packet reception. This is due to increased CBR leading to higher rates of packet collisions. The total number of received packets can be an important metric for evaluating different congestion control algorithms. However, it is also important to analyze where those packets are originating from. For each vehicle receiving BSMs (ego vehicle), we divided its neighboring vehicles into three groups. The first (nearest) group consists of vehicles that are at a distance of 100 m or less from the ego vehicle. The second (third) group consists of vehicles that are at a distance of 100 m to 300 m (300 m to 500 m) from the ego vehicle. These threshold distances for grouping neighboring vehicles were chosen  
Figure 5: Comparison of received BSMs with DRCC vs. constant bitrates. Figure 6: Comparison of received BSMs with DRCC vs. existing approaches. by us to show the distribution of received BSMs from vehicles at different distances. In general, messages from neighboring vehicles that are closer to the ego vehicle are more relevant than those from distant vehicles. Figure 7 shows the average number of messages from vehicles at different distances for the proposed algorithm, constant bitrates, and other existing techniques. We can see that under high loads none of the approaches receive packets beyond 300 m; however, for TDRC, there are no received packets beyond 300 m for TDRC even under low loads. This is because TDRC uses a higher data rate in such cases compared to other approaches, resulting in low CBR (<0.2) and higher RSSI requirements. Typically, the nearest vehicles, i.e., within a radius of 100 m from the ego vehicle, have the greatest impact.