# Adjacent Vehicle Number-Triggered Adaptive Transmission for V2V Communications
## 4 Numerical Results  
The performances are evaluated in terms of BER, frame error rate (FER), and throughput. The number of transmitted bits or frames is used for the BER and the FER, respectively. However, note that the number of total generated frames is considered for the throughput, since the generated but un-transmitted frames need to be considered. In this paper, the measure of reliability can be interpreted in terms of throughput defined in Equation (4). This is because the throughput here reflects not only the successfully transmitted bits but also the total generated bits including un-transmitted bits. Thus, the higher throughput shows the un-transmitted bits for N = 0 are compensated with the higher order modulation. Therefore, we can say the reliability gets improved in terms of the throughput. For example, a user in the vehicle can enjoy a reliable and stable stream video service, even if the vehicle cannot be connected to the other vehicles in a certain time period. The simulation results presented in Figures 4-7, where the X axis is the energy per bit to noise power spectral density ratio (Eb/N0). \[\text{BER}=\frac{\text{Number of unsuccessfully transmitted bits}}{\text{Number of transmitted bits}}, \tag{2}\]  
\[\text{FER}=\frac{\text{Number of unsuccessfully transmitted frames}}{\text{Number of transmitted frames}}, \tag{3}\]  
\[\text{Throughput}=\frac{\text{Number of successfully transmitted frames}}{\text{Number of total generated frames}}, \tag{4}\]  
Figure 4: Error rate performance of V2V scenario I in a Rician fading channel a with a constant K-factor value (10 dB): the (**a**) BER performance and the (**b**) FER performance. Figure 5: Throughput performance of V2V scenario I in a Rician fading channel with a constant K-factor value (10 dB). Figure 4 shows the BER and FER results for scenario I. In Figure 4a, the BER of the proposed method is higher than that of conventional methods 1 and 2 but slightly lower than that of conventional method 3. Similar results were seen for the FER performance in Figure 4b. This is because the lower the modulation level is, the more robust against noise and interference it becomes. Therefore, in the conventional methods, the relatively lower level modulation shows a lower error rate. Since the proposed method randomly combines two different modulations, the error performance is also combined and located between the conventional methods 2 and 3. Note that the main objective is not the error performance but the overall performance in terms of the throughput. That is, it is more important that how much data is successfully delivered to other vehicles in terms of the throughput. In Figure 5, the throughput performances are presented. When the Eb/N0 is larger than 6.5 dB, the proposed method shows better performance than the conventional methods 1 and 2 but shows worse performance than the conventional method 3. Below 6.5 dB, the proposed scheme provides a lower throughput than the conventional method 2 but a higher throughput than the conventional method 3. Regarding conventional method 1, the maximum throughput performance is below 50%, since they transmit the data very slowly and fail to compensate for the throughput degradation when N = 0 (i.e., no connectable vehicle around). Therefore, the throughput reaches a relatively lower cap, which means the service cannot be provided adequately for this case. Even though 16 QAM in conventional method 2 can bring the maximum throughput up to 76%, the throughput loss of  
Figure 6: Error rate performance of V2V scenario II in a Rician fading channel with various K-factor values: the (**a**) BER performance and the (**b**) FER performance. Figure 7: Throughput performance of V2V scenario II in a Rician fading channel with various K-factor values. 24% still makes the users suffer from discontinuity. On the other hand, the maximum throughput of conventional method 3 reaches near 97%.