## 4 Structure and Operation of Coded Laser Pilots-Based HILPB WPT System  
The proposed HILPB WPT system comprises of multiple PTXs and PRXs. PTXs mounted on traffic lights at intersections perform vehicle-to-infrastructure (V2I) communication with EVs. Upon receiving a request from an EV, a PTX sends its power channel information (PCI) as a coded laser pilots using each available WPC. The EV selects a PTX based on the PCI. The selected PTX emits HILPB using the designated WPC, which is a laser beam propagation path from a PTX to a PRX and its location is expressed by the spherical coordinates of the laser emission angle.  
The energy conversion efficiency is decreased with increased PV cell temperature and a large part of the absorbed laser energy would dissipate into heat. According to the law of energy conservation, the sum of the thermal-related energy from light-to-heat generation and the electrical energy from light-to-electricity conversion should basically equal the absorbed laser power. These two energy forms of thermal and electrical energy are intrinsically competing for counterparts. The temperature and the thermal stress in the PV array are determined by the heat generated from the absorbed laser energy, which in turn instantaneously determine the light-to-electricity conversion efficiency. The higher the convective heat transfer, the more electrical power would be obtained. The PV array is located on the top of the roof. PTX is placed at the traffic light which is a higher place than the vehicle, so the roof is best seen in a line of sight at traffic signals. The roof is the flattest and widest part of the vehicle. The wider the roof, the more PV array can be installed, and the more power can be received, the more energy can be received. Because the roof is exposed to the outside, it has an excellent natural heat dissipation effect through convection, and artificial cooling using various methods is also possible [36].  
The PRX mounted on the EV performs V2I communication with the surrounding infrastructure, including traffic lights, and converts the HILPB received from the PTX via an embedded PV array into PCI or power. To avoid hazards due to the HILPB, the EVs are not in motion and are halted at the intersections, waiting for the signal to turn green. When the power supply is drained, the PRX receives and analyzes the PCI sent by the PTXs and selects the optimal PTX and WPC for power transmission. Figure 8 illustrates the overall structure of an HILPB-based multiple WPT environment comprising four PRXs and 12 PTXs. Each of the four PTXs at each crossroad has its maximum transmission power (MTP) and WPC, and the transmission distance and incident angle vary according to the geometric relationship between the PTX and PRX, resulting in different amounts of power delivered to the PRX at each transmission event. Depending on the amount of required power, a PRX can generate more than one power transmission path by selecting more than one PTX.  
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Suitable Experimental Setup** & **Setup \#1** & **Setup \#2** & **Setup \#3** & **Setup \#4** \\ \hline Standard deviation of irradiation & 0.0098 & 0.0067 & 0.0068 & 0.0052 \\ Standard deviation of power & 0.0053 & 0.0037 & 0.0029 & 0.0019 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Standard deviation of the difference between the mathematical model and measured values.  
However, one of key problems is the accurate positioning of the PTX and PRX to achieve the highest PTE. If the positioning is not accurate, it leads to power losses and consequently a low PTE is obtained. Figure 9 shows a scenario involving four PTXs and one PRX where the positioning is not proper on the PV array. The circled area outside the PV array leads to the power losses and reduces the PTE. In the given scenario, only T1 can provide the highest PTE concerning its positioning accuracy with the PV array, while T1, T2, and T3 lead to power losses, assuming that all PTXs possess the same power capacity.