# LoRa Architecture for V2X Communication: An Experimental Evaluation with Vehicles on the Move
## 6 Outdoor Testing and Analysis of the Prototypes
### Power and Energy Analysis  
As the proposed architecture facilitates modularity, the existing vehicles do not need any extra circuitry or change in vehicle infrastructure to be enabled with V2X. These vehicles can keep the OBU on board and power it up with a small battery to be in the designed architecture. As it is designed to provide legacy vehicles with V2X communication capability, energy efficiency is another major concern. To improve energy efficiency, the units are designed with low power micro-controller chips and LoRa transceivers. Tables 6 and 7 denote the power consumption and energy consumption respectively for both unencrypted and encrypted data transmission. The table shows that the average power consumption of OBU with unencrypted and encrypted data is 341.2 mW and 346.15 mW respectively. This power consumption is very less compared to the task it is performing. On the other hand, RSU consumes less than half of the power that OBU consumes. The power consumption of the RSU is 164.3 mW and 169.25 mW, respectively, with unencrypted and encrypted data communication. The energy consumption for each packet of data transmission is also very efficient. The encrypted communication of each data packet draws the energy of 0.037 J and 0.018 J respectively for OBU and RSU. With a battery of 3.7 V and a capacity of 10,000 mAh with 10% \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Unit**} & \multicolumn{2}{c}{**Unencrypted Data (mW)**} & \multicolumn{3}{c}{**Encrypted Data (mW)**} \\ \cline{2-7}  & **Max.** & **Min.** & **Mean** & **Max.** & **Min.** & **Mean** \\ \hline OBU & 681.3 & 303.3 & 341.2 & 703.3 & 322.7 & 346.15 \\ RSU & 505.45 & 123.1 & 164.3 & 598.9 & 123.1 & 169.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Power consumption for data transmission. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Source of Variation** & **SS** & **df** & **MS** & **F** & \(p\)**-Value** & **F crit** \\ \hline SS P-RSU & 0.177778 & 2 & 0.088889 & 0.5 & 0.611496 & 3.31583 \\ SS VS & 212.3111 & 4 & 53.07778 & 298.5625 & 1.08E-23 & 2.689628 \\ SS Interaction & 1.155556 & 8 & 0.144444 & 0.8125 & 0.59726 & 2.266163 \\ SS Within & 5.33333 & 30 & 0.177778 & & & \\ Total & 218.9778 & 44 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: ANOVA table for two factorial design. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Unit**} & \multicolumn{2}{c}{**Unencrypted Data (mW)**} & \multicolumn{3}{c}{**Encrypted Data (mW)**} \\ \cline{2-7}  & **Max.** & **Min.** & **Mean** & **Max.** & **Min.** & **Mean** \\ \hline OBU & 681.3 & 303.3 & 341.2 & 703.3 & 322.7 & 346.15 \\ RSU & 505.45 & 123.1 & 164.3 & 598.9 & 123.1 & 169.25 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Energy consumption for data transmission. discharge safety, the driving hours with a single charge can be calculated by (3). The running hours of both OBU and RSU are presented in Table 8.  
\[\textit{Driving hours}=\frac{\text{BatterCapacity}-\text{(BatterCapacity}\times \text{DischargeSafetyRate)}}{\text{Average Current Consumption}} \tag{3}\]  
These results reflect excellent energy efficiency for both OBU and RSU. The calculated running time of the OBU are almost half of the RSU as the OBU is equipped with sensors causing it to draw more current. Even though with encrypted data transmission, an OBU can offer up to 130 h of driving time with a 1000 mAh, 3.7 V battery. On the contrary for the same setup, an RSU can operate up to 266 h with a single charge of the battery, so if a person drives for two hours on average, a 10,000 mAh battery can support an OBU for more than two months before the battery needs to be replaced whereas RSU can last more than 4 months. The proposed system is also compared with the other state-of-the-art LoRa V2X models in Table 9 to analyze important functionalities of the architecture like- reliability, latency, energy, security, prototype designing, and evaluation of the systems.