## 2 Background and Related Work
### Leveraging VLC for Intelligent Traffic Solutions  
The V-VLC system, as depicted in Figure 1a, utilizes a mesh cellular hybrid structure with two controllers. The \"mesh\" controller at streetlights relays messages to vehicles,while the \"mesh/cellular\" hybrid controller at the traffic lights acts as a border-router for edge computing [22; 23].  
The system integrates a modulated light transmitter and a PIN-PIN-based receiver to enable wireless communication. Figure 1b illustrates the relative positions of the emitter and receivers, along with a coverage map depicting footprint regions (#1-#9) within the unit cell and their corresponding steering angles (\(\delta\)). The transmitter employs ON-OFF Keying (OOK) amplitude modulation to modulate light emitted from tetra-chromatic white LEDs (WLEDs) positioned at the corners of square unit cells. These WLEDs combine Red (R: 626 nm), Green (G: 530 nm), Blue (B: 470 nm), and Violet (V: 390 nm) light to produce white illumination [24].  
Each WLED channel generates calibrated wavelength signals, enabling up to four independent emitters per unit. The receiver detects combinations of two (#3, #5, #7, #9), three (#2, #4, #6, #8), or four (#1) optical signals, resulting in 24 distinct combinations and 16 unique photocurrent levels [20]. A PIN-PIN demultiplexer filters the signals, decoding the transmitted message based on prior amplitude calibration [25].  
Figure 1: (**a**) 2D representation of the V-VLC architecture. (**b**) V-VLC Emitter and receivers’ relative positions and illustration of the coverage map with the footprint regions in the unit cell (#1–#9) and steering angle codes (2–9) [22].  
The architecture supports Infrastructure-to-Cloud (I2 IM) communication through embedded platforms for processing and sensor interfacing, as well as peer-to-peer Vehicle-to-Vehicle (V2V) communication for data sharing. Streetlights act as geo-transmitters spaced 20 m apart, emitting I2V messages, including synchronization, physical IDs, and traffic data. Vehicles and pedestrians entering a streetlight's range receive a unique identifier qi(x,y,t) along with traffic updates.  
Intersection management utilizes queue/request/response mechanisms and temporal/spatial relative pose concepts. Vehicles or pedestrians approaching intersections send crossing requests (V/P2I). Traffic signals acknowledge these (I2V/P) and assign occupancy trajectories within footprint regions (Figure 1b). Collision risks delay acknowledgments until resolved. Vehicle speeds are tracked using transmitter IDs, while mesh nodes estimate relative poses qij(t) for neighboring vehicles [26]. Requests also include position, direction, and speed, with leader-follower data supporting request confirmation. Delays are analyzed based on queue lengths within cells at the start and end of green phases (Figure 1a).  
The VLC system ensures real-time monitoring of pedestrians, vehicles, and infrastructure. Key metrics, such as queue formation and pedestrian density at corners, are evaluated to enhance safety. P2I2P communication facilitates travel time estimation, while transmitter tracking IDs provide insights into speed and waiting times.