Songnan Bai

Vehicular Multi-Hop Broadcasting Protocol for Safety Message Dissemination in VANETs

Most safety-related applications targeting at Vehicular Ad-hoc Networks (VANETs) use Vehicle-to- Vehicle (V2V) broadcast method to disseminate safety- related information to all surrounding vehicles. However, the conventional broadcast schemes have the broadcast storm problem which can lead to unbearable transmission delay and packet loss. In this paper, we present an efficient broadcast scheme referred as Vehicular Multi-hop broadcasting Protocol (VMP) for fast dissemination of safety message within the critical area. The core of the VMP is that it designates multiple reliable forwarders with differentiated forwarding delay, and exploits cooperative forwarding mechanism to help the forwarding when the specified forwarders fail to transmit the alert message. With the realistic simulation studies, the VMP demonstrates better performance than previous contention-based schemes by reducing end-to-end delay and message rebroadcasting ratio while keeping high message reception rate.

Context awareness beacon scheduling scheme for congestion control in vehicle to vehicle safety communication

Abstract Vehicle safety applications based on vehicle to vehicle communication typically transmit safety-related beacons to all neighboring vehicles with high reliability and a strict timeline. However, due to high vehicle mobility, dynamic network topology and limited network resource, this periodic beaconing could lead to congestion in the communication network. Therefore, beacon transmission method has a special challenge to efficiently use the limited network resources to satisfy the requirements of safety applications. With this motivation, we propose a novel distributed beacon scheduling scheme referred to as the context awareness beacon scheduling (CABS) which is based on spatial context information dynamically scheduling the beacon by means of TDMA-like transmission. The proposed beacon scheduling scheme was evaluated using different traffic scenarios within both a realistic channel model and IEEE 802.11p PHY/MAC model in our simulation. The simulation results showed that the performance of the CABS scheme was better than periodic scheduling in terms of packet delivery ratio and channel access delay. Also, the CABS scheme satisfies the requirements of the safety applications.

A MIH Services Based Application-Driven Vertical Handoff Scheme for Wireless Networks

Since the future wireless communication environments will contain various wireless access technologies, the provision of seamless mobility to vehicle across these heterogeneous networks is needed. In this paper, we propose an application-driven vertical handoff scheme which includes PMIPv6 handoff process by using IEEE 802.21 Media Independent Handoff (MIH) services to provide seamless connectivity in heterogeneous wireless networks. Both the lower layers’ information of neighbor access networks obtained by MIH services and the QoS requirements of the application are compared to choose the most suitable candidate network for the application. In addition, our scheme put great emphasis on vehicle mobility consideration on handoff network selection due to the vehicle predominant characteristic of moving around dynamically.

Enhanced Selective Forwarding Scheme for Alert Message Propagation in VANETs

Recently vehicular safety applications have been introduced to improve traffic safety and efficiency. These applications are classified into two types: safety-oriented and non-safety applications. In this classification, safety-oriented applications are usually provided by means of vehicular multi-hop broadcasting in order to support reliable and fast alert message propagation to all surrounding vehicles when an emergency event occurs on a road. In VANETs, broadcast-based packet forwarding is usually preferred in order to propagate urgent traffic-related information to all reachable nodes within a certain dangerous region. However, this approach may cause broadcast storm problem, which can lead to serious contention in transmission between adjacent nodes. With this motivation, in this paper, we propose an alert message propagation scheme based on selective forwarding that aims at i) minimizing the number of rebroadcasting nodes, and ii) guaranteeing reliable and fast alert message delivery to all reachable nodes. The proposed scheme is evaluated using two types of highway scenarios. The simulation results show that the proposed scheme performs better than existing broadcast schemes in terms of message delivery latency, message delivery ratio, and message rebroadcasting ratio.

A structured TDMA-based V2I MAC protocol for automated guided vehicle control systems

Recently, IEEE 802.11p based vehicular communication has been widely studied in different area of vehicular applications. In this paper, we mainly focus on the automated guided vehicle (AGV) applications which have a strict communication requirement for very low transmission delay and very high reliability. However, CSMA-based 802.11p standard has problems with unbounded channel access delay and multiple consecutive packet losses due to random access the channel without any control. With this motivation, this paper proposes a novel TDMA-based MAC protocol in order to deliver the vehicle control information with high reliability and bounded latency to satisfy the proposed V2I based AGV system. The proposed TDMA-based MAC protocol is evaluated in comparison with the IEEE 802.11p, i.e., WAVE standard. Simulation results show that the proposed MAC protocol is performed better than IEEE 802.11p in terms of end-to-end delay and packet delivery ratio in desired vehicular applications.

Beacon-based cooperative forwarding scheme for safety-related inter-vehicle communications

Most safety-related applications targeting Inter-Vehicle Communications systems (IVC) rely on multi-hop broadcasts to disseminate safety-related information to all surrounding vehicles. However, these conventional broadcast schemes suffer from the so-called ”broadcast storm” problem, a scenario in which contention and collisions happens a lot due to an excessive number of broadcast packets. In this paper, we propose a novel solution, referred to as the Beacon-based Cooperative Forwarding (BCF) scheme for fast and reliable propagation of safety message within a critical area. With the aid of periodic beacons, the proposed scheme specifies multiple appropriate forwarder candidates to broadcast the alert message before detecting a danger. Moreover, a cooperative forwarding scheme is also proposed to guarantee high reachability and to delay constraints. After realistic simulations, the BCF scheme demonstrated better performance than other contention-based schemes by reducing the end-to-end delay and message rebroadcasting ratio by over 30% while maintaining a high message reception rate.

Movement-aware alternative path routing protocol for vehicular multi-hop communications

Vehicular Ad-hoc Networks (VANETs) are now considered to be suitable for enhancing road safety and efficiency in vehicular environment. Especially, due to the affluent spectrum resource, supports for non-safety relevant services, like inter-vehicle entertainments, are also under investigation. However, in the vehicular environments, the nodes can experience frequent link breakages due to the vehicle mobility characteristic. Thus, a reliable multi-hop routing protocols is definitely needed to overcome the performance degradation caused by it. In this paper, we propose a novel scheme for non-safety applications, which is also referred as Movement-aware Alternative path Routing Protocol (MARP), a reactive unicast routing protocol that considers two factors such as vehicle movement and multi-path to determine the optimum reliable routing paths. In addition, we devote special attention to the random characteristic of the radio propagation model to provide a simulation with the desired level of realism. After realistic simulation studies, the performance of proposed MARP routing protocol outperforms the traditional VANETs routing by reducing the routing overhead and enhancing the stability of routing path.