# Enhancing Heterogeneous Communication for Foggy Highways Using Vehicular Platoons and SDN
## 3 Proposed Scheme: SDVN for Foggy Highways
As a result, the RSU with the lowest \(MD_{controller}\) is chosen to be the LC at each layer from the MC. Figure 2 illustrates a tree-based topology where the MC is the parent node and RSUs at various levels from the MC are the child nodes. The RSU positions are exact depictions of their actual location on the highway, as highways do not have RSUs like signboards, streetlights, or cameras located in the same place. From (1), it is evident that \(HM\) represents the total number of hello messages that each RSU receives from the vehicles within its communication range. The higher the number of vehicles within an RSU range, the greater the likelihood of it being chosen as the LC. For the selection of HV, we assume that vehicles that are moving on the road at the same speed and have the same destination can be part of a platoon. The HV vehicle in our scheme can be led by a driver who knows how to drive in critical situations, maintains speed, and has strong psychological attributes. These driver attributes will be added to our experiment as an extension of this paper. In this article, we consider the first on the road in a platoon as the HV. To explain our algorithm in detail, we use an example scenario in which MC has selected all LCs and HVs (see Figure 1). The visibility on the highway becomes low as the platoons proceed towards the foggy region. Figure 1 shows two platoons moving on the road at different speeds and facing different visibility regions. The communication range of an LC encompasses each platoon. PAMs are exchanged between platoons through LCs (if two platoons are not within communication range) and within the platoon directly using DSRC. These PAMs include platoon ID, vehicular ID, \((x,y)\), \(vel\), \(vis_{c}\), and \(t\). The HV collects the current status (vehicle ID, \((x,y)\), \(vel\), \(vis_{c}\), and \(t\)) of all vehicles within its platoon and forwards this computed information to the nearby LCs. Since LCs are connected directly through LTE, this locally collected information is shared with the  
Figure 2: Decision tree for selecting local controllers. MC and with only LCs involved in the optimal routing path (to decrease the periodic exchange of messages). Thus, based on a limited exchange of control packets, which ultimately reduces network overhead, MC creates a global network view. Different cases are considered below to test the validity of our proposed scheme in low-visibility scenarios. Case (i): High Connectivity--When There Are Platoons on the Highway and They Are in Proximity to the LCs  
As can be seen in Figure 1, platoon A enters a low visibility region where HV instructs all its members to slow down their speed. Before it instructs its members, the LC has already sent a PAM to the HV to reduce its speed due to low visibility ahead. Let us assume that a source vehicle in platoon B, at its current position, intends to communicate with the destination vehicle in platoon A to learn about the road conditions (or visibility conditions) at the location where platoon A is moving. The source vehicle sends a request message to its HV first, and then the HV asks its nearby LC (within communication range \(CR\)), by sending a _packet_in_ message, to find an optimal routing path to platoon A (see Figure 1). This optimal path is calculated as follows:  
\[Path_{optimal}=max(PT_{p}), \tag{2}\]  
where the path-time (\(PT\)) is calculated using link-duration (\(LD\)). If the link is between platoon to platoon or platoon to LC, it is \(LD_{platoon}\), and if it is between LC to LC, it is \(LD_{controller}\), such that  
\[PT_{p}=min(LD_{pc(1,p)},LD_{pc(2,p)^{\prime}},,LD_{pc(l,p)}), \tag{3}\]  
where \(pc\) represents either platoon or controller, based on the communication technology, \(l\) represents the total number of relay nodes, which is usually LCs, but there is a possibility that HVs and members can become relays between two communicating platoons (see next case). \(p=1,2,\ldots,P\) represents all possible paths \(P\) between two communicating platoons.