Enhanced Framework for Priority-Based Scheduling in VANETs for Emergency Message Delivery and Network Optimization

Abstract

Vehicular Ad-hoc Networks (VANETs) support road safety and intelligent transportation by enabling vehicle-to-vehicle and vehicle-to-infrastructure communication, but the high mobility and dynamic topology of these networks make it difficult to guarantee timely delivery of safety-critical messages under heavy channel contention. This study proposes an Enhanced Fair Priority-Based Scheduling (EFPBS) framework that combines message-priority classification, fairness-aware queue servicing, and adaptive congestion monitoring to improve Quality of Service (QoS) in VANETs. EFPBS was implemented and evaluated in NS-3 integrated with SUMO for realistic vehicular mobility, using the IEEE 802.11p protocol stack across vehicle densities of 50 to 200 nodes. Its performance was benchmarked against conventional First-In-First-Out (FIFO) scheduling and static Priority-Based Scheduling (PBS) using packet delivery ratio (PDR), end-to-end delay, throughput, fairness index, and packet drop ratio. At the highest tested density (200 vehicles), EFPBS achieved a packet delivery ratio of 25.47%, the highest among the three schemes (compared with 21.97% for FIFO and 25.07% for PBS), the lowest packet drop ratio (74.53%), the highest throughput (2.27 Mbps), and the highest fairness index (0.673). These gains were achieved while sustaining a stable average end-to-end delay of approximately 4.85 ms across all densities and all three schemes, indicating that the improvements in reliability and fairness did not come at the cost of increased latency. The results show that FIFO scheduling is highly sensitive to fairness collapse under moderate density, that static PBS improves delivery only inconsistently, and that EFPBS provides the most stable and scalable behaviour of the three schemes as vehicle density increases. The findings suggest that fairness-aware, congestion-adaptive scheduling is a more viable direction for emergency message delivery in dense VANETs than either arrival-order or static-priority approaches, while also indicating that further gains in absolute delivery ratio are needed before large-scale real-world deployment.