Adaptive Location Division Multiple Access for reliable safety message dissemination in VANETs

IEEE 802.11-based Vehicular Ad Hoc Networks (VANETs) are becoming important in enhancing road traffic safety. Drivers can proactively detect and avoid unsafe situations using safety message disseminated by VANETs. There are two common dissemination techniques: event-triggered multi-hop relaying (flood) and periodic one-hop broadcast (beacon). A basic idea of Location Division Multiple Access (LDMA) has been proposed to mitigate the broadcast storm problem in flood dissemination. However, it has not yet provided practical schemes applicable to a real vehicular environment. Moreover, if flood and beacon traffics coexist in a single channel, the reliability of beacon-type traffic can be significantly degraded during the broadcast storm of flood traffic even if LDMA mitigates the storm. We propose Adaptive LDMA (A-LDMA) that 1) mitigates the broadcast storm problem of flood traffic and 2) isolates beacon traffic from the storm in order to achieve a consistent reliability of safety messaging. Performance evaluation is conducted through ns-2 simulation with aim of understanding 1) the performance of LDMA for beacon and flood traffics, 2) the performance impact of LDMA´s design parameters and mobility, and 3) the feasibility of using LDMA for traffic isolation. In our simulation, A-LDMA improves the delivery rate of individual broadcasts during the broadcast storm from 40% to 60% for flood and to 80% for beacon.