# A Packet Collision Reduction Based on Reselection for LTE V2X Mode 4
## 4 Numerical Examples  
### Simulation Environment  
In this paper, we use the traffic flow simulator SUMO (Simulation of Urban MObility) [41] to simulate the behavior of the UEs and update the position of each UE every 100 ms. For the mobility simulation of UE traffic, a highway scenario is used as shown in Figure 10. The highway length is equal to 5 km, the lane width is equal to 4 m, and each way has three lanes. We use the central 2 km as the evaluation range.  
The received power is calculated using the WINNER+ B1 propagation model [42]. The propagation loss \(PL\) [dB] in the WINNER+B1 model is calculated as follows:  
* for \(10<d<d^{\prime}_{BP}\): \[PL=22.7\log(d)+27+20\log(f_{c}),\] (3)
* for \(d^{\prime}_{BP}<d<5000\): \[PL=40\log(d)+7.56-17.3\log(h^{\prime}_{t})-17.3\log(h^{\prime}_{r})+2.7\log(f_{ c}),\] (4)  
where \(d\) is the distance between the transmitter and the receiver in meters, and \(f_{c}\) is the carrier frequency in GHz. The effective antenna heights \(h^{\prime}_{t}\) and \(h^{\prime}_{r}\) are computed as follows: \(h^{\prime}_{t}=h_{t}-1.0\) m, \(h^{\prime}_{r}=h_{r}-1.0\) m, where \(h_{t}\) and \(h_{r}\) are the actual antenna heights at the transmitter and the receiver, respectively. The parameter \(d^{\prime}_{BP}\) is calculated as follows:  
\[d^{\prime}_{BP}=\frac{4h^{\prime}_{t}h^{\prime}_{r}f_{c}}{c} \tag{5}\]  
where \(c\) is the speed of light, and the value is 299792458 m/s in a vacuum. Although the speed of light decelerates slightly in air, the deceleration is usually negligible. \(d^{\prime}_{BP}\) means  
Figure 10: Highway scenario.  
Figure 9: An example of the OA method.  
the breakpoint distance, and it is well known that the radio propagation has different characteristics after the breakpoint distance. Therefore, in Equations (3) and (4), the propagation loss must be divided into cases with \(d^{\prime}_{BP}\) as a boundary. In consideration of the effective range of the WINNER+ B1 model, if \(d\) is less than 10 m, the propagation loss is calculated as \(d=10\) m. The path loss is used to calculate the Signal to Interference Noise Ratio (SINR) for each received packet. The packet error rate [43] based on the estimated SINR is used to determine the success or failure of packet reception. In this paper, channel fading and shadowing are not considered for the basic verification of the proposed methods.  
The simulation parameters are set as listed in Table 3. These parameters are applicable for normal ITS radio propagation. Probability \(p_{k}\) to keep the same resource is set to 0.0. This means that the reselection is always performed when the RC reaches 0. Selection window widths \(T_{1}\) and \(T_{2}\) are set so that the selection window is the maximum. Threshold \(P_{th}\) is set to the lowest possible value. The bandwidth, carrier frequency, packet size, transmission power, noise figure, antenna height, and antenna gain are according to the 3 GPP evaluation scenario [44]. The number of subchannels is set to 2 assuming Quadrature Phase Shift Keying (QPSK) and coding rate 1/2 for the bandwidth. The RRI is determined at the time of UE generation based on probability \(p_{g}\) as shown in Tables 4-6, and it is not changed after the generation.  
For performance evaluation, Packet Reception Rate (PRR) [44] is used. The PRR is calculated as follows:  
\[\text{PRR}_{d_{1},d_{2}}=\frac{\sum_{n=1}^{N}X_{d_{1},d_{2}}^{n}}{\sum_{n=1}^{N} Y_{d_{1},d_{2}}^{n}} \tag{6}\]  
where \(Y_{d_{1},d_{2}}^{n}\) is the number of UEs located in the range \([d_{1},d_{2})\) from the transmitter for the \(n\)-th (\(1\geq n\geq N\)) packet, and \(X_{d_{1},d_{2}}^{n}\) is the number of UEs with successful reception among \(Y_{d_{1},d_{2}}^{n}\).