# Performance Analysis of the IEEE 802.11p Multichannel MAC Protocol in Vehicular Ad Hoc Networks
## 5 Model Validation and Numerical Analysis
Figure 9: _Cont._  
Figure 10 analyzes the performance of safety and WSA messages on the CCH and the performance of non-safety messages on the SCHs in detail. The configurations parameters are: \(R_{d}\) = 6 Mbps, \(\lambda_{e}=\lambda_{s}=5\) packets/s, \(p_{br}=10^{-5}\), \(L_{e}\) = 200 Bytes, \(L_{s}\) = 160 bits, \(L_{data}\) = 2000 Bytes, \(L_{cs}\) = 400 m, safety-related packet: AIFSN[0] = 3, \(W_{e}\) = 8 and WSA packet: AIFSN[1] = 6, \(W_{s,0}\) = 16. Figure 10a-c shows the packet transmission delay and PRR of safety-related and WSA packets with different parameters on the CCH, and the throughput of non-safety packets with different parameters on the SCHs in the IEEE 1609.4 standard. We can observe the following: (1) A higher channel data rate can reduce transmission delay greatly and enhance reliability, at the same time, improve the throughput greatly. On the one hand, this is due to the fact that a higher channel data rate can shorten the packet transmission time, and thus reduce the chances of contentions on the CCH which the conflict probability on the CCH is reduced ultimately. On the other hand, a higher channel data rate can transmit more packets on the SCHs in a short time. (2) With the decrease in the packet arrival rate, the PRR increases significantly, and the packet transmission delay is also reduced. Moreover, the throughput enhances greatly with the decrease of the packet arrival rate. This is due to the fact that the lower packet arrival rate decrease the collision probability and shortens the backoff blocking time, and thus nodes have more opportunities to make SCH reservation and the number of successful reservations rises. (3) Increasing the bit error rate can decrease the PRR sharply, and the  
Figure 9: Average packet transmission delay and PRR on the CCH, and throughput on the SCHs: (a) packet transmission delay on parameter configurations 1��: (b) packet transmission delay on parameter configurations 2�: (c) packet transmission delay on parameter configurations 3�: (d) packet transmission delay on parameter configurations 4�: (e) PRR on parameter configurations 1�: (f) PRR on parameter configurations 2�; (g) PRR on parameter configurations 3�; (h) PRR on parameter configurations 4�: (i) throughput on parameter configurations 1�: (j) throughput on parameter configurations 2�: (k) throughput on parameter configurations 3�; and (l) throughput on parameter configurations 4�. throughput also is cut down. This is because the length of a safety-related packet is greater than that of a WSA packet, and thus the effect of bit error rate on the transmissions of safety-related packets is greater than that of WSA packets according to Equation (6). The increase of the bit error rate has no effect on the packet transmission delay. (4) The decrease in the size of safety-related packets has a positive effect on both the packet transmission delay and the reliability. However, the performance gain in terms of throughput increases with the increase of non-safety packet size, and this is because each transmission of non-safety packet with long payload carries more data than that of non-safety packet with short payload. (5) With the increase in the carrier sensing range, both the PRR and the throughput rise significantly, however, the packet transmission delay increases. On the one hand, this is because that the larger carrier sensing range can handle the hidden terminal problem effectively, however, the tagged vehicle also has to supervise more nodes, and thus, leads to a longer service time of packets. On the other hand, the increasing PRR can suppress the packet transmission delay which matter less to the number of successful SCH reservations as the increase of the carrier sensing range, which leads to the increase of throughput on the SCHs ultimately. Figure 10d,e shows how the CW and AIFSN affect the reliability and performance of the network.