# Experimental Demonstration of MmWave Vehicle-to-Vehicle Communications Using IEEE 802.11 ad
## 5 Experimental Result  
### Coverage and Beam Measurement  
Prior to the driving experiment, we evaluated the performance of the IEEE 802.11 ad module on static vehicles in terms of beam coverage and directions. For this measurement, the transmitter (i.e., vehicle) and receiver (i.e., laptop) were separated by 2 m, and continuous data traffic was transmitted from the transmitter to the receiver. The Tensorcom module supports only two sectors for beam forming, which covers \(\pm\)30\({}^{\circ}\) and 60\({}^{\circ}\), respectively. We selected one of these sectors and transmitted dummy packets over the air. Then, we measured the received SNR in 360\({}^{\circ}\) of directions around the transmitter. Figure 7 shows the measured beam strength in SNR. The beam angle spreading over \(\pm\)30\({}^{\circ}\), as shown in Figure 7a, was appropriate for the convoy model of vehicles without interfering with other vehicles  
Figure 6: Campus and city routes for measurement. Figure 7: Measured beam patterns and SNR. in adjacent lanes. Another beam sector covered \(\pm 60^{\circ}\), as shown in Figure 7b. The signal strength was the strongest at \(\pm 45^{\circ}\), where the two main lobes were created, while the SNR at approximately \(0^{\circ}\) demonstrated a much lower value of \(-10\) dB. This beam pattern was suitable for the diagonal connection model illustrated in Figure 1b. The SNR of the main and side lobes at the beam \(\pm 30^{\circ}\) case of the beam was approximately \(12\) dB and \(-10\) dB, respectively. Similarly, the receiver SNRs of the main lobe and side lobe at \(\pm 60^{\circ}\) were approximately \(11\) and \(-10\) dB, respectively. As the antenna directivity depends on the number of antennas in the array, the gain was comparable between the two beam patterns. The main lobe width was observed at nearly \(60\) degree in both patterns. The vehicles could switch between the two sectors according to change in the GiV2V topology. **Observation 1. ** A pair of nodes using the IEEE 802.11 ad standard with a directional antenna could achieve the required SNR only by the main-lobe and not by side-lobes. We measured the received SNR of the boresight of \(\pm 30^{\circ}\) beam for varying distances between the transmitter and receiver. For distances within \(5\) m at the boresight, the SNR was more than \(5\) dB, while the SNR was approximately \(0\) dB at distances from \(5\) to \(10\) m, as illustrated in Figure 8. In areas farther than \(10\) m, the SNR varied with fading between \(-5\) and \(-10\) dB. Note that the SNR was less than \(-10\) dB outside the beam angle. **Observation 2. ** The gain difference between the main and side lobes was more than \(15\) dB in IEEE 802.11 ad beam forming. In addition, we measured the required SNR for each MCS level; we recorded the SNR values with which the 802.11 ad module began to receive packets even with certain errors, while changing the distances between the transmitter and receiver nodes at each MCS level. According to Table 4, MCS 3 or 4 level was achievable at less than \(5\)-\(6\) m. After approximately \(10\) m, only MCS 0 or MCS1 was available. Table 5 lists the pathloss exponents calculated by the measured SNR values and approximate distances, as shown in Figure 8. The mean value of the pathloss exponents was \(2.09\), which was nearly same as a known pathloss exponent of the LOS. In addition, the measured SNR = \(-1\) dB for MCS1 was available at approximately \(10\) m and its pathloss exponent was \(2.1\). Table 3 also indicates that the reachable distance could be approximately \(10\) m with the \(\alpha\)= \(2.1\). Therefore, we can conclude that the theoretical calculation and measurement were almost identical, although there might be a little error in measurement. \begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline MCS & 0 & 1 & 2 & 3 & 4 & 5 & 6 & 7 \\ \hline SNR (dB) & \(-10\) & \(-1\) & 2.5 & 4.5 & 6 & 7.5 & 8.5 & 9.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Measured SNR against MCS level.