Energy-efficient fragmentation-aware dual adaptive collision-free bit mapping MAC protocol for VANET

In the present work, an enhanced energy-efficient medium access control (MAC) protocol is proposed for adaptive data traffic conditions in VANET. The earlier adaptive collision-free MAC-bit map assisted (ACFM-BMA) protocol effectively integrated electric vehicle (EV) battery levels and buffer status to optimize communication efficiency and energy conservation. However, a key limitation was the underutilization of allocated slots by certain devices. To address this, we introduce the adaptive bit-map assisted protocol (ACFM-ABMA MAC), where each slot is dynamically fragmented into four subslots using two additional control bits, allowing vehicles to request only the required portion of a slot (e.g., 00 for 25% up to 11 for 100%). This fine-grained allocation reduces slot wastage, ensures better channel utilization, and further enhances energy savings. The proposed protocol is analyzed under low, moderate, and high data traffic scenarios, considering vehicle density, periodic traffic generation, and event-driven traffic probabilities. Simulation results confirm that ACFM-ABMA MAC achieves superior energy efficiency, and bounded latency across low, moderate, and high event-driven traffic scenarios.