MAC-aware Routing Protocols for Vehicular Ad Hoc Networks: A Survey

International audienceThe constantly growing number of vehicles on our roads has become an increasing major cause of serious injury and death. Efficient data dissemination in Vehicular Ad hoc Networks (VANETs) inevitably requires an efficient and robust routing protocol. In this context, several categories of routing protocols have been proposed in the literature to meet VANETs application requirements in terms of delay, packet loss and throughput. In this paper, we focus on cross layer routing protocols. We present a survey of state-of-the-art MAC aware routing protocols designed for VANETs. These solutions can broadly be divided into two categories: contention-free and contention-based MAC-aware routing. In this paper we carryout a comprehensive comparison of these approaches. Finally, we identify open research issues that should be addressed in order to improve MAC aware routing techniques in VANETs

An Efficient Cross-Layer Design for Multi-hop Broadcast of Emergency Warning Messages in Vehicular Networks

International audienceThe main objective of Vehicular ad hoc networks (VANETs) is to make road transportation systems more intelligent in order to anticipate and avoid dangerous, potentially life-threatening situations. Due to its promising safety applications, this type of network has attracted a lot of attention in the research community. The dissemination of warning messages, such as DENMs (Decentralized Environmental Notification Messages), requirse an efficient and robust routing protocol. In previous studies, the active signaling mechanism has shown its ability to prevent collisions between users trying to allocate the same resource. In this paper, we propose an original message forwarding strategy based on the active signaling mechanism. Our proposal disseminates warning messages from a source vehicle to the rest of the network while minimizing the access delay and the number of relay nodes. For this purpose, a special time slot is dedicated to forwarding emergency warning messages. To avoid access collisions on this slot, the active signaling scheme we propose favours the selection of the furthest node as the forwarder. We carry out a number of simulations and comparisons to evaluate the performances of the scheme

Structural, optical and dielectric properties of Cu1.5Mn1.5O4 spinel nanoparticles

In this study, a Cu1.5Mn1.5O4 spinel was successfully synthesized by a sol-gel method at 500 °C for 5 h and characterized by different techniques. X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectroscopy and Raman spectroscopic analyses confirmed the formation of a spinel cubic structure with the Fd3̄m space group. The SEM proves that the grain size of our compound is of the order of 48 nm. Crystallite sizes determined from three estimates are closer to the grain size obtained from the SEM, indicating the single domain nature of the sample. The optical properties of UV-visible spectroscopy for our sample showed that the gap value is equal to 3.82 eV, making our compound a good candidate for optoelectronic applications. For electrical properties, impedance spectroscopy was performed at a frequency range of 40 ≤ frequency ≤ 106 Hz. This suggested hoping conduction due to three theoretical models. The latter can be attributed to the correlated barrier hopping (CBH) model in region I, overlapping large polaron tunneling (OLPT) in region II and non-overlapping small polaron tunneling (NSPT) mechanism in region III. One dielectric relaxation is detected from the dielectric impedance and modulus, attributed to grain contributions. This behavior was confirmed by both Nyquist and Argand's plots of dielectric impedance at different measuring temperatures