## 4 Structure and Operation of Coded Laser Pilots-Based HILPB WPT System
### Power Transmitter (PTX)  
A PTX is a device mounted on a traffic light for V2I communication between the HILPB-based WPT and EVs, and uses a spherical coordinates as shown in Figure 10. A 36 bit PCI specific to each PTX comprising 1 bit is allocated to the start signal, 5 bit each are allocated to the PTX ID and PRX ID, 7 bit each to the IDs of the two parts (polar angle \(\theta\) and azimuthal angle \(\phi\)) of the WPC available for transmission, 8 bit to the MTP per 10 W, and 3 bit to checksum or cyclic redundancy check (CRC), as shown in Figure 11. The WPC IDs indicate the emission direction of the laser beam in the spherical coordinate system. The CRC, which is used for detecting accidental changes in PCI, can be generated from the PRX ID, PTX ID, WPC, and MTP. Figure 8: Block diagram of a multiple WPT environment using HILPB and V2I transmission. Figure 9: Scenario showing the power losses caused by positioning inaccuracy between the PTXs and PRX. The PTXs transmit their respective PCI to the PRXs through laser beams within the Class 1 maximum permissible exposure (MPE) range in the detection step and transmit their MTP through HILPB in the transfer step. They receive messages from the PRXs in real-time around the clock via V2I communication. DS-OCDMA has been designed to provide multiple and simultaneous access to optical systems. DS-OCDMA has been examined already in environments requiring an address or user identification in various optical applications [37; 38; 39; 40; 41; 42; 43]. The PCI transmitted from a PTX comprises DS-OCDMA-encoded data designed to make one PCI orthogonal to the others, given that different sets of information are simultaneously sent from multiple PTXs. DS-OCDMA uses spread spectrum communication and digital modulation. The former is based on a unipolar synchronous prime sequence code and the latter is based on the nonreturn-to-zero (NRZ) on-off keying (OOK). Assigning a unique code to each of the 25 PTXs with different 5 bit device ID numbers is ensured by using synchronous prime sequence codes with a weight of 7 and a code length of 49. The operation of a PTX is divided into standby, detection, and transfer steps as marked in red, green, and blue, respectively, in Algorithm 1. In the standby step, the PTX is waiting for a PCI request message via V2I from a PRX. On receiving a PCI request message, it proceeds to the detection step and transmits its unique PCI encoded with DS-OCDMA in a laser beam within Class 1 MPE, which constitutes a safe level of exposure. A PTX sequentially transmits one encoded PCI after another using one channel each from the WRCs available for transmission. While all PTXs simultaneously proceed with the detection step on receiving a PCI request message, they have different end times because the number of WPCs available varies from one PTX to another. Upon completion of PCI transmission via all available WPCs, the PTXs return to the standby step and only the ones that receive the transfer start message from a PRX initiates the transfer step. A PRX analyzes the PCI transmitted by the PTXs in the detection step, selects the optimal PTX, and sends a transfer start message to the selected PTX, thereby designating the WPC for the given transmission. Thus, the selected PTX transmits the MTP through HILPB using the designated WPC. Upon receiving the transfer stop message from the PRX, it stops the transmission and returns to the standby step. EVs in the near future are constantly monitoring the outside of the vehicle through various sensors, such as radar or LiDAR, so it is possible to predict the occurrence of accidents caused by a collision. In addition, the vehicle can immediately  
Figure 11: Unique PCI packet format transmitted from a PTX. Figure 10: Laser beam direction and position as determined for each PTX channel. detect an external shock, such as a collision of another vehicle or motorcycle, and this can be requested to stop the power supply to the PTX through V2I.