# UAV-Assisted Hybrid Scheme for Urban Road Safety Based on VANETs
## 3 UAV Assisted (UAVa) Reactive Protocol Strategy
### UAVa's Design Approach
#### 3.2.1 Uava's Network Architecture
Another is dynamic current-time information accumulated from nodes through VANETs or transportation infrastructure, such as traffic surveillance cameras and detection circuits. Connected nodes upload dynamic information via V2R communication or V2U communication, such as sudden traffic congestion caused by unexpected accidents. At the intersection, the traffic monitoring camera and detection circuits track and record real-time traffic information, which includes road density and number of nodes, and then upload the real traffic information to the RSUs at the intersections. Complex traffic details are automatically updated on the entire road network. In our proposed UAVa's network architecture, RSUs at intersections cover a limited communication area, inside this coverage area the RSU receives the node's request and response, the node arrives at this coverage area and requests to RSU for current-time traffic information through VANETs. RSU shares current traffic information through our designed current-time traffic information accumulation and sharing mechanism, designed to accumulate and share current-time traffic information across the entire road network. The node calculates the travel time estimate and selects the shortest route from the source to the destination through [PERSON]'s famous greedy shortest path planning algorithm. Once sudden congestion occurs, immediately current-time traffic information is updated to the entire network. Then the control room will take immediate action, and they launch a UAV to this congested intersection. The UAV will assist RSU in this congested intersection to enhance the coverage area of this intersection, and create a backpressure strategy to avoid new congestion and fixed-route interruption among the source to the destination node. By using the routing table, the source node can modify or revise the route again, and the source node can select the second shortest route for the destination. Our proposed UAVa algorithm is briefly described in Algorithm 1. ```
1:BEGIN
2:/* Initialization*/
3:Vehicle\(\leftarrow\)(Vid, Ncij)//Ncij - Vehicles Current Intersection
4:Define Source \(\leftarrow\)Vcl, Destination \(\leftarrow\)Vdl/\(\l\)cl - Current Location, dl- Destination Location
5:Input Find Shortest Route (Vcl Vdl)
6:/* Initialize: [PERSON]'s Algorithm */
7:Create intersection set w
8:for intersection v in map:
9:distance[v] \(\leftarrow\infty\)
10:visited[v] \(\leftarrow\) Not Visited
11:add v to w
12:distance[source] \(\leftarrow\) 0
13:if w =! = 0 then
14:u \(\leftarrow\) Intersection in w with minimum distance[u]
15:update u from w
16:for neighbor intersection v of u:
17:distance[alt] \(\leftarrow\) distance[u] + length (u, v)
18:if distance[alt] \(<\) distance[v] then
19:distance[v] \(\leftarrow\) distance[alt]
20:visited[w] \(\leftarrow\) u
21:/*select the shortest route*/
22:Input Vid(request) The Real Time Traffic Information \(\leftarrow\) Nij(information)
23:If Destination Intersection Ndij = 0 then//Ndij-Destination Intersection
24:Follow the Selected Route
25:else
26:Revise and Replan Route ACK(information)//ACK-Acknowledgment
27:id\(\leftarrow\) ACK (information)
28:Revise and Re-plan the Route (Vcl Vdl)
29:Select the Second Minimum Route
30:/* Avoid Traffic Congestion */
31:if*t*RSU Capacity Overflow */
32:RSU(send-packet) > ACK(receive-packet)
33:RSU(send-packet) = | = ACK(receive-packet) then
34:RSU(send request for-UAV) CLN(receive UAV request-UAV + 1)//CLN--Cellular Network
35:CLN(request-UAV + 1) CR(receive-UAVrequest)//CR--Control Room
36:CR Send the UAV to the Congested Intersection. 37:OUTPUT: Enhance RSU Capacity. 38:END
```  
**Algorithm 1** Accumulation of Real-Time data