Tatsuaki Osafune

Multi-Hop Vehicular Broadcast (MHVB)

Inter-vehicular communications (IVCs) are now considered as a way to realize active safety, for example, by providing the position information of each other or the potential danger warning by wireless communications. We have worked on a flooding protocol over vehicular ad hoc networks (VANETs) to efficiently disseminate the information for the sake of active safety applications, such as the positions and the velocities of the vehicles. We propose a flooding protocol with (i) congestion detection algorithm which suppresses unnecessary packets due to vehicular congested traffic and (ii) Backfire algorithm which efficiently forwards the packet through the network by selecting the adequate receiver node based on the distance from the original node. In this paper, we show simulation results over NS2 (network simulator 2). They show that the proposed flooding protocol significantly improves the performance of data dissemination over VANETs

Enhanced Functions of 802.11 Protocol for Adaptation to Communications between High Speed Vehicles and Infrastructures

There are many researches on the mobile network based on IEEE 802.11 wireless devices. While wireless LAN devices are commonly used, they have been originally designed for office use and have no support for high mobility. Hence, the association establishment (the channel scanning of mobile nodes and the auth/association frame exchange between mobile nodes and access points) and the handoff often fails when we try to utilize the device for the communication between high speed vehicles and infrastructures. We proposed the method that realizes rapid association establishment and optimized handoffs to solve the problems in a compatible form with 802.11 protocol. We realized the proposed method by modifying the standard 802.11 specification of client side. On the evaluation in the actual environment, we showed better thoroughput with the proposed method than the one with the standard 802.11 specification.

Floating car data system enforcement through vehicle to vehicle communications

The paper presents a new application enabled by vehicle-to-vehicle (V2V) communication systems; our target is to combine V2V with floating car data (FCD) systems and merge advantages of both: the V2V application warnings to enhance the FCD traffic information precision as well as the information availability; inversely, V2V communication can also benefit from the FCD system and offer some large-scale road network traffic information. We present some architecture modifications which are needed to realize this new application, both in terms of in-vehicle components as well as the networking requirements. The proposed approach is to be built upon the existing infrastructure of FCD system to lower the implementation cost

Performance measurement of mobile ad hoc network for application to Internet-ITS (intelligent transportation system)

We evaluated the performance of an ad hoc network in a mobile environment in order to access its feasibility as an infrastructure for vehicle-to-Internet communication services. To realize this kind of service. The infrastructure should provide wide range where the service is available. We expected that by using an ad hoc network, spatial service range, connection time to the access point while driving, and amount of data transferred from the access point would be better than in existing public wireless LAN services. In the experiment, three cars acted as mobile nodes, and we measured the connection time to the access point and the amount of data that could be given via the access point. The result confirms the feasibility of using an ad hoc network as an infrastructure for vehicle-to-Internet communication services.

RSVconf: Node Autoconfiguration for MANETs

A mobile ad-hoc network (MANET) is a self-configuring network of mobile nodes connected by wireless links, which can form an arbitrary topology. We have worked on a new protocol, RSVconf, to ensure the IP address self-configuration of MANETs, with a special focus on the ITS (intelligent transportation system) context which is indeed the most mobile scenario. The RSVconf protocol manages the creation, merger and remerger (merger after part of the network temporarily separated) of networks at IP layer. It is stateful, distributed and routing independent. The simulation results show its capability to react fast and correctly to the rapid topology changes of mobile networks without a waste of bandwidth. In this paper we present the current status of our research, open aspects and future directions

Effect of Decentralized Congestion Control on Cooperative Systems

Vehicular cooperative systems are expected to provide a promising solution for enhancing active safety of vehicles. It requires stable and secure wireless communications for mutual information exchange among vehicles. In order to realize stable and secure communications, packet loss due to collisions need to be suppressed and communication apparatus should be ensured to perform proper cryptographic verification of packets. Because the hardware constraints in cooperative systems allow only a limited rate for cryptographic processing of packets, congestion control acts as a key technology to solve these challenges. This paper proposes a congestion control algorithm for vehicular cooperative systems to control the packet reception rate at a communication apparatus of a vehicle. The proposed algorithm is evaluated quantitatively by network simulation. The results show that the proposed algorithm can stabilize the packet reception rate by controlling the packet transmission rate on surrounding vehicles in a decentralized manner.

Analysis of an epidemic dissemination protocol for ad hoc networks

We have worked on an epidemic dissemination protocol to maintain soft-state in a decentralized, peer-to-peer fashion, in ad hoc networks. This protocol is an enhancement of passive distributed indexing (PDI) method proposed by Lindemann and Waldhorst. We have enhanced PDI in order to reduce the number of broadcast messages when the search for an item may span several hops. Three enhancements are proposed: (i) lazy query propagation to delay the propagation of query messages such that local responses can inhibit unnecessary search. (ii) Quench waves to stop an already initiated query propagation when still possible. Decision rules based solely on local information determine whether to start a quench wave or not. (iii) The use of multi-point relay (MPR) or similar protocol and algorithm, to reduce redundant broadcast messages.