# Distributed Triggered Access for BSM Dissemination in 802.11 bd V2V Networks
## 4 Performance Evaluation  
In this section, we discuss the performance evaluation of the proposed scheme is discussed. For the performance evaluation of the proposed scheme, an event-driven MAC level simulator has been developed in Matlab which implements IEEE 802.11 EDCA functions and IEEE 802.11 ax TUA functions based on the proposed physical layer numerology of IEEE 802.11 bd discussed in Section 2. In the tested scenario, all VSTAs are located on a one-dimensional highway with the total length of 5000 m as depicted in Figure 4, and the performance is measured for the centered 3000 m. It is assumed that the VSTAs are equipped with a Global Positioning System (GPS) and the wireless communication module with parameters shown in Table 1. In the simulation, the rate of successful packet transmission of DTA and the conventional EDCA are compared. As discussed in Section 2, since an ideal physical channel condition is assumed, the packet error rate and the mobility of VSTAs are not considered, the main focus is the performance impact of packet collision given the VSTA density varies from 0.03 to 0.12. Following the typical characteristics of BSM traffic employed in related works [21; 26; 27; 33; 42], 200 Bytes payload size and 10 Hz arrival rate BSM traffic is considered to be moderate data traffic in the simulation. In addition, in order to emulate future platooning environments with higher requirements, 400 Bytes payload size and 20 Hz arrival rate BSM traffic is used for the simulation as heavy data traffic. To observe the trade-off between the number of multiplexed VSTAs and the airtime of the TB PPDU, 3 and 9 RUs per one DTA sequence are tested. Figure 7 shows the active BSM transmission success rate of the proposed scheme that a BSM is transmitted and delivered to all receivers within the PD range. According to the figure, DTA always shows better performance than the legacy 802.11p EDCA scheme as long as the contention window size and the number of scheduled RUs per transmission is large enough. In case of low vehicle density, the proposed scheme guarantees successful delivery for greater than 90% of the generated BSMs, and in the most extreme case, high vehicle density (0.12) and heavy data traffic (\(R_{BSM}\): 400 B, \(\lambda\): 20 Hz), DTA successfully transmits more than 20% of the generated BSMs improving the transmission success rate by twice of EDCA performance. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Highway length & 5000 m \\ Vehicle density (\(\beta\)) & 0.03, 0.06, 0.09, 0.12 (vehicle/meter) \\ PD range (\(L_{pd}\)) & 300 m \\ ED range (\(L_{ad}\)) & 400 m \\ Triggering range (\(L_{tr}\)) & 100 m \\ BSM arrival rate (\(\lambda\)) & 10, 20 Hz \\ Transmission bandwidth & 10 MHz \\
11p data subcarrier & 48 subcarriers \\
11p OFDM symbol duration & 8 \(\upmu\)s \\ Number of RUs for DTA & 3, 9 RUs \\
11 bd data subcarriers per RU & 72 (9 RUs), 24 (3 RUs) \\
11 bd OFDM symbol duration & 32 \(\upmu\)s \\ Legacy preamble duration & 40 \(\upmu\)s \\
11 bd preamble duration & 48 \(\upmu\)s \\ Data rate & 12 Mbps \\ Trigger frame MAC payload & 38 Bytes \\ CTS frame MAC payload & 17 Bytes \\ BSM MAC payload (\(R_{BSM}\)) & 200, 400 Bytes \\ Slot time & 13 \(\upmu\)s \\ SIFS & 32 \(\upmu\)s \\ AIFS & 58 \(\upmu\)s \\ Contention window size & 256, 2048 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. Figure 7: Active BSM transmission success rate. One remark is that as soon as the EDCA channel access intensity dominates the effect of the contention window, the performance degrades fast because the extended duration of TB PPDU makes it more vulnerable from hidden VSTAs transmission. Therefore, setting an appropriate contention window size can be critical to fully exploit the advantages of DTA. Figure 8 depicts the average BSM collecting delay for which a VSTA collects BSMs of all VSTAs within the PD range.