# Vehicular Visible Light Communication for Intersection Management +
## 3 V-VLC Vehicular Communication
### Scenario and Architecture  
A V2X communication link, in a two-way-two-way traffic light-controlled crossroad, was simulated. Typical four-legged intersections are linked to sixteen roads: eight roads incoming from and eight roads exiting to neighboring crossroads north, west, south, and east. In Figure 2a, the lighting plans of a standard intersection are shown, while in Figure 2b the corresponding plan for a split intersection is displayed. The generated joint footprints in both crossroad regions (LED array = RGBV-modulated color spots) are also inserted. The split intersection (Figure 2b) starts with only one main street that connects two crossroads (Intersection 1-Intersection 2). Road request and response segments, offer a binary (turn left/straight or turn right) choice. Moreover, vehicle's movement is known in each intersection and can be anticipated, considering the flow dependencies between two closely spaced signals. In coordinating traffic signals it is assumed that a vehicle's movement along a main street (\(W>>\) E) is known and can be anticipated. Knowing when a vehicle is going to pass intersection \"1\" allows for a green light to be pre-programmed for that vehicle's direction of travel. The two intersections are referred to as one entity, the interchange. Signal timing refers not only to the phasing patterns at the two intersections, but also to the cycle length and offset relationship between them. The two controllers provide high flexibility since they allow the use of all phasing patterns for both intersections [16].  
To build the I2V, a simplified cluster of unit square cells in an orthogonal topology that fills the service area is proposed [28]. The grid size was chosen in order to avoid an overlap in the receiver from the data in adjacent grid points. The considered geometric scenario in the experimental results uses a smaller size square grid (2 cm), to improve its practicality. Each transmitter, \(X_{i,j}\), carries its own color, \(X\) (RGBV) as well as its horizontal and vertical ID position in the surrounding network (\(i\),\(j\)). In the Proof of Concept (PoC), it was assumed that the standard crossroad is located in the intersections of line 4 with column 3 (Figure 2a) and the split one in the intersection of line 4 with column 3 and 7 (Figure 2b). The emitters are located at the nodes along the roadside. Thus, each LED sends an I2V message that includes the synchronism, its physical ID and the traffic information. In response to the streetlight signal, the receiver assigns a unique ID and the traffic message to the probe vehicle when it enters the streetlight captures range.  
Figure 2a displays the imposed four traffic flows: From west (W), vehicles \(a\), \(c\), and \(d\) approach the crossroad, vehicle \(a\) with straight movement, vehicle c and vehicle \(d\) with left turns. From east (E), vehicle \(b\) approaches the intersection with left turn only. From south (S) vehicle \(e\), oncoming, has a right-turn approach. In the fourth flow, vehicle \(f\), coming from north, goes straight. In coordinating traffic signals vehicle's movement along a main street can be predictable as in Figure 2b. In the design of a coordinated system two-directional flows were considered. One from the west (W) with the same three vehicles (\(a\), \(c\), \(d\)) approaching Intersection 1. In the second flow, vehicle \(b\) from east (E) approaches Intersection 2 with straight movement and Intersection 1 with left turn only. The third traffic flow was shifted to Intersection 2. Vehicle \(e\), oncoming from south (S) Intersection 2, has a right-turn approach while in the fourth flow, vehicle \(f\), coming from north goes straight in Intersection 1.