Mitigation of packet duplication in VANET unicast protocols

Vehicular ad hoc networks (VANETs) are self-organized networks designed to improve the drivers' safety and the efficiency of vehicular traffic management. In this kind of networks, packet losses are common in the path from source to destination, mainly due to the high mobility of the nodes (i.e., vehicles). Reliability mechanisms at different layers are used to mitigate the impact of this issue. In this work, we explain how the loss of acknowledgment frames (ACK) at the medium access control (MAC) layer with the recovery procedure of VANET routing protocols lead to an unexpected generation of duplicate packets. We propose two incoming filters with different levels of detection of duplicate packets at routing layer to prevent the propagation of unnecessary packet copies, so that the available bandwidth will increase as a consequence. To evaluate the behavior of our proposals, we employed two VANET routing protocols: the topological iAODV [1] and the geographical MMMR [2]. We carried out simulations with three vehicle densities in an urban scenario and with two different mechanisms to adapt the size of the contention window (CW), which is an important factor in VANETs to avoid collisions. The extensive statistical analysis of the results show that our approaches are effective to reduce the traffic load in both routing protocols in terms of routing operations, idle time, duplicate packets and end-to-end delay. We also observed an expected minimum degradation of the packet delivery ratio in the geographical routing protocol, thus the benefits of the proposal are clear.