# Vehicular Visible Light Communication for Intersection Management +
## 4 V2X Cooperative System Evaluation  
### Communication Protocol and Coding/Decoding Techniques  
To code the information, an On-Off keying (OOK) modulation scheme was used and it was considered a synchronous transmission based on data frame of 64 bits. A data frame is exemplified in Figure 6.  
If the transmitter is a streetlamp or headlamp, the frame is divided into four blocks; if the transmitter is the traffic light, five blocks are considered. The first block is the synchronization block [10101], the last is the payload data (traffic message) and a stop bit ends the frame. The ID block gives the location (\(x\), \(y\) coordinates) of the emitters inside the array (\(X_{i,j}\)). Cell's IDs are encoded using a 4 bit binary representation for the decimal number. The \(\delta\) block (steering angle (\(\delta\))) completes the pose in a frame time \(q(x,y,\delta,t)\). Eight steering angles along the cardinal points and coded with the same number of the footprints in the unit cell (Figure 1b) are possible from a start point to the next goal. If the message is diffused by the IM transmitter, a pattern [0000] follows this identification, if it is a request (R) a pattern [00] is used. The decimal numbers assigned to each ID block are pointed out in Figure 6a. So, in this time slot, R\({}_{3,4,Sw}\); G\({}_{3,3,Sw}\); B\({}_{4,4,Sw}\) and V\({}_{4,3,Sw}\) are the transmitted  
Figure 5: Phasing diagram: (**a**) Color poses. (**b**) Four-legged intersection. (**c**) Split intersection.  
node packets, from the crossroad 1. Here, the driver receives his request message [pose, and traffic needs] from the infrastructure. This allows it movement across the crossroad to southwest (code 8), directly from the current point (#1) to the goal point (#8).  
Based on the measured photocurrent signal by the photodetector, it is necessary to decode the information received. For this purpose, a calibration curve is previously defined to establish this assignment. In Figure 6b, calibration curve that uses 16 distinct photocurrent thresholds resultant from the combination of the RGBV-modulated signals from the VLC emitter is plotted [29]. The correspondence between each footprint and the photocurrent level is highlighted on the right side of Figure 6b. Here, the MUX signal obtained at the receiver as well as the coded transmitted optical signals is displayed. The message, in the frame, start with the header labelled as Sync, a block of 5 bits [10101] imposed simultaneously to all the emitters. In the calibration block (second block), four calibrated R, G, B, and V optical signals are transmitted at the same time. Here, the bit sequence was chosen to allow all the _on/off_ sixteen possible combinations of the four RGBV input channels (24). In the last block, a random message is transmitted. A periodic retransmission of the calibration curve is needed to ensure the correspondence to the output signal and an precise decoding of the transmitted information. Comparing the calibrated levels (d\({}_{0}\)-d\({}_{15}\)) with the assigned 4-digit binary [RGBV] codes, ascribed to each level (pointed out at the right side of Figure 6b), the decoding is straightforward, and the  
Figure 6: (**a**) Frame structure representation of a request message. (**b**) MUX/DEMUX signal of the calibrated cell. In the same frame of time, a random signal is superimposed.  
message decoded. Taking into account the frame structure (Figure 6a), after decoding the MUX signals, the pose (position and direction), the kind of transmitter (IM or Vehicle) and traffic message are revealed [30].