Omar Chakroun

Deterministic access for DSRC/802.11p vehicular safety communication

In this work, we present the design of an efficient Deterministic medium Access (DA) for Dedicated Short-Range Communication (DSRC) vehicular safety communication over IEEE 802.11p, called Vehicular DA (VDA). VDA supports two types of safety services (emergency and routine safety messages) with different priorities and strict requirements on delay, especially for emergency safety messages. VDA processes both types of safety messages to maintain a balance between two conflicting requirements: reducing chances of packets collisions and lowering the transmission delay. To avoid long delays and high packets collisions, VDA allows vehicles to access the wireless medium at selected times with a lower contention than would otherwise be possible within two-hop neighborhood by the classical 802.11p EDCA or DCF schemes. Particularly, our scheme provides an efficient adaptive adjustment of the Contention Free Period (CFP) duration to establish a priority between emergency and routine messages. Simulations show that the proposed scheme clearly outperforms the classical DCF scheme used by 802.11p in high-offered load conditions while bounding the transmission delay of safety messages.

Pedestrian collision avoidance in vehicular networks

Main applications in vehicular networks are primarily looking for road safety improvement. To achieve this goal, positiondata information of all interfering road users must be conveyed effectively. This proposal examines the performance made possible using WAVE/DSRC standard when including pedestrians/two-wheels. First, we propose a specific message format for encapsulating pedestrian and two-wheel position-data information. Second, we propose a complete system for collision avoidance at intersection level. Subsequently, we perform tests to analyze the system performance in terms of packets reception rate and transmission delay using WAVE/DSRC standard in two modes of operation. Namely, we perform a comparison between using only the control channel to announce and forward messages as a safety service, and using one of the dedicated channels 172 or 184 after announcing the service on the control channel. Taking into account different levels of network densities, we investigate the modes of operation that provide lower congestion and channel saturation. The findings in this work are relevant to the design of data transmission patterns for pedestrian collision avoidance systems at intersections when using VANETs.

Overhead-free congestion control and data dissemination for 802.11p VANETs

Direct radio-based vehicle-to-vehicle communication can be used to prevent accidents by letting vehicles exchange information about their state, intentions, and the road conditions. Although it is now a standard, the IEEE 802.11p protocol for vehicular ad hoc networks (VANETs) has known shortcomings. Dissemination is not reliable over distances higher than 300 m and congestion in the communication channel can lead to very low rates of safety messages delivery. Multi-hop routing and access channel techniques are well known approaches that were separately investigated to improve network effectiveness. However, achieving low end-to-end latency with multi-hop techniques is usually at the cost of lower data delivery rates, which in turn causes problems for the effectiveness of safety services embedded in vehicles. In this paper, we introduce a new dissemination and congestion avoidance scheme for safety messages over IEEE 802.11p VANETs. In order to ensure good delivery rates beyond 300 m, the approach propagates information over two hops while avoiding the resulting congestion by using a fully distributed asymmetrical transmit power adjustment technique. The scheme uses two time-dependent optimization-under-constraint processes to elect the best vehicle to act as a relay for data forwarding. The scheme can estimate the probability of reception rate (PRR), and adjust the forwarding distance to meet the minimum requirements of PRR and delivery distance to fit specific safety application requirements. The proposed solution, unlike previous dissemination techniques, works simultaneously on reducing congestion due to multi-hop relaying and on ensuring low end-to-end delay. Simulation results confirm the effectiveness of the proposed adaptation and relaying scheme and its advantageous network performance compared to others, under various traffic constraints.

RMDS: Relevance-based messages dissemination scheme for 802.11p VANETs

Vehicular ad hoc networks (VANETs) leverage communication equipment and infrastructure to improve road safety. These networks, by the rapid change of their topology and their broadcasting dissemination nature, can experience mainly two major problems; (1) the broadcasting storm and (2) network disconnection. In this paper, we focus on safety-related messages and propose a new approach to avoid the broadcasting storm and under various network load. Our scheme, called RMDS, is based on two main concepts; the critical distance and the distance of relevance. It combines an asymmetric power-range adjustment and message frequency tuning aiming to reduce network load. It integrates a new approach to prioritize locally generated messages over relayed ones according to the distance from the event originator. Simulation results confirm the effectiveness of the proposed scheme and its network performance under various traffic constraints.

MUDDS: Multi-metric Unicast Data Dissemination Scheme for 802.11p VANETs

Vehicular ad hoc networks (VANETs) leverage communication equipment and infrastructures to improve road safety. These networks, by the rapid change of their topology, can experience mainly two major problems; (1) the broadcasting storm and (2) the network disconnection due respectively to high vehicles density and their velocity. In this paper, we propose a new unicast data dissemination scheme based on distances estimation using Received Signal Strength (RSS) measurements and congestion detection by mean of a newly designed metric; called Multi-metric Unicast Data Dissemination Scheme (MUDDS). MUDDS adapts the transmission range so that congestion can be avoided. It performs the best available link choice to guarantee both reliable transmission and minimum delivery delay. MUDDS focuses on the broadcasting storm and the network disconnection problems simultaneously. Simulation results confirm the effectiveness of the proposed on-demand adaptation and relaying scheme and its impact on network performance under various traffic constraints.

Indoor and outdoor localization architecture for pervasive environment

Location awareness is one of the key aspects for pervasive computing environments. It enables location data to be accessed and used anywhere by any application. Major challenges to design effective localization solutions are pervasive deployment and support for heterogeneous technologies. In our efforts to design an effective localization solution, we present a dynamic and efficient infrastructure independent layered architecture. The architecture is highly distributed, integrates inference engine to provide best location estimation for multiple technologies. Our architecture is efficient and comes across challenges in localization process such as computational power, reusability and components dependency.

Studying the impact of DSRC penetration rate on lane changing advisory application

Vehicular communication technology leverages communication equipment and infrastructure to improve road safety and provide useful services for road user. In order to operate properly, many of these services need continuous data gathering to assess road situations accurately. In this paper, we analyse the impact of communication technology penetration rate and the proportion of application-equipped vehicles on the efficiency of a Lane Changing Advisory Application in improving travel delay and traffic fluidity. We model the system analytically and perform extensive simulations at different penetration rates both with a microscopic traffic simulator and a network simulator. Vehicle-to-vehicle communication outcomes influence application efficiency and therefore driver behaviour. The mobility pattern is fed back into the traffic simulator in a closed loop in order to assess traffic fluidity. The results of the study present the impact of DSRC penetration ratio on the application performance and by consequence on road traffic fluidity. They show that even at low penetration rates of 10% and 25%, total travel time and traffic fluidity are enhanced.

Investigating the Use of Message Reneging in Multi-hop 802.11p VANETs

Abstract Vehicular ad hoc networks (VANETs) are becoming an important technology to enable enhanced road safety. Based on the 802.11p standard model, VANETs are known to suffer from channel congestion when the number of vehicles increases. Also, problems of fading and channel loss conditions on the road, make the effective delivery rate in VANETs very low beyond distances that are half of the transmission range. In this paper, we are interested in multi-hop message delivery in VANETs to extend the delivery range of safety messages beyond a one-hop range. We investigate the use of priority to favor on-hop messages over relayed ones according to the distance from the event originator. We also investigate the effect of using a limited delay in messages queues versus message reneging with such a scheme. An analytic and simulation study show interesting results under various constraints.

Enhancing safety messages dissemination over 802.11p/DSRC

Direct radio-based vehicle-to-vehicle (V2V) communication can be used to prevent accidents and to provide accurate information on road state or surrounding vehicles intention. Both kinds of information can be used to enable drivers to react in time and avoid hazardous situations. While the IEEE 802.11p standard has specifically been adopted for vehicular communications, its Distributed Coordination Function (DCF) operation can cause poor delivery rates when the communication channel is congested or when messages need to be transmitted over distances higher than 300 meters. In this paper, we propose MORS, a technique for transmission power adjustment to avoid channel congestion, combined with an efficient multi-hop data dissemination scheme. The purpose is to ensure low delays and high delivery rates for V2V communications at distances higher than it would normally be possible with the same effectiveness with 802.11p alone. The power adjustment technique is fully distributed and asymmetrical, and the multi-hop data dissemination scheme is based on a newly designed multi-metric which characterizes the available links capacity. MORS determines, at each hop, the best available link choice to ensure both reliable transmissions and a minimum delivery delay while reducing congestion and network load though adaptive power adjustment. Simulation results confirm the effectiveness of the proposed transmit-power adaptation and multi-hop relaying schemes under various realistic traffic constraints.

Interoperability between Deterministic and Non-Deterministic Vehicular Communications over DSRC/802.11p

In recent works, a priority-aware deterministic access protocol that is based on 802.11p/DSRC was introduced to allow vehicles to access the shared medium in collision-free periods. The VANET Deterministic Access (VDA) protocol as introduced in [8] has no mechanism that prevents a non VDA-enabled vehicle from accessing the channel in a scheduled VDA opportunity (VDAOP). A non VDA-enabled vehicle, i.e. a vehicle not configured with the optional VDA capability over 802.11p, may start transmitting on the shared channel just before or during the VDAOPs reserved for vehicles with VDA capabilities. Also, non VDA-enabled vehicles may be prevented from accessing the shared channel due to the transmission of VDA-enabled vehicles during their respective VDAOPs with a higher priority (shorter AIFS). In this work, we propose a new enhanced VDA scheme, called EVDA that avoids the above issues and prevents interfering transmissions from VDA-enabled vehicles and non VDA-enabled vehicles. We also analyzed the impact of several design tradeoffs between the Contention Free Period (CFP)/Contention Period (CP) Dwell-time ratios on the performance of safety applications with different priorities with EVDA. Simulations show that the proposed scheme clearly outperforms the VDA scheme in high communications density conditions while bounding the transmission delay of safety messages and increasing the packet reception rate.