Satoshi Ohzahata

Flexible, Portable, and Practicable Solution for Routing in VANETs: A Fuzzy Constraint Q-Learning Approach

Vehicular ad hoc networks (VANETs) have been attracting interest for their potential uses in driving assistance, traffic monitoring, and entertainment systems. However, due to vehicle movement, limited wireless resources, and the lossy characteristics of a wireless channel, providing a reliable multihop communication in VANETs is particularly challenging. In this paper, we propose PFQ-AODV, which is a portable VANET routing protocol that learns the optimal route by employing a fuzzy constraint Q-learning algorithm based on ad hoc on-demand distance vector (AODV) routing. The protocol uses fuzzy logic to evaluate whether a wireless link is good or not by considering multiple metrics, which are, specifically, the available bandwidth, link quality, and relative vehicle movement. Based on an evaluation of each wireless link, the proposed protocol learns the best route using the route request (RREQ) messages and hello messages. The protocol can infer vehicle movement based on neighbor information when position information is unavailable. PFQ-AODV is also independent of lower layers. Therefore, PFQ-AODV provides a flexible, portable, and practicable solution for routing in VANETs. We show the effectiveness of the proposed protocol by using both computer simulations and real-world experiments.

Fuzzy logic based multi-hop broadcast for high-density vehicular ad hoc networks

Vehicular ad hoc networks have been attracting the interest of both academic and industrial communities on account of their potential role in Intelligent Transportation Systems (ITS). In vehicular ad hoc networks, vehicles are usually located quite densely within the range of radio transmission. In this paper, we propose a fuzzy logic based multi-hop broadcast protocol for information dissemination in high-density vehicular ad hoc networks. The proposed protocol exhibits low message overheads by means of using only a subset of neighbor nodes to relay messages. In the relay node selection, the proposed protocol jointly considers multiple metrics of inter-vehicle distance, node mobility and signal strength by employing the fuzzy logic. We use computer simulations to evaluate the performance of the proposed protocol.

Controlling File Distribution in the Share Network Through Content Poisoning

Peer-to-Peer (P2P) file sharing applications have dramatically increased in popularity for the past few years. Although a P2P file sharing network shares many files, it does not usually have a management and control mechanism for the files exchanged. Consequently, copyright infringement and malware propagation in P2P file sharing networks have become prevalent. In order to prevent these file distribution, content poisoning has attracted much attention recently. Although content poisoning aims to obfuscate users by diffusing a lot of poisoned chunks in P2P networks, its effect to the networks have not been well studied yet. In this paper, we apply content poisoning to “Share”, one of the most popular P2P file sharing applications in Japan, to control its file distribution. Our evaluation includes how effective our proposed content poisoning method to a live Share network composed of over 100,000 active peers. The evaluation result shows that our content poisoning method decreases the number of peers that complete file download to less than 5% compared to the case without our control. Our content poisoning method also reduces additional traffic required for poisoning to 4%.

A low latency path diversity mechanism for sender-oriented broadcast protocols in VANETs

Abstract In vehicular ad hoc networks, many applications require a low latency and high reliability especially the safety applications. Reliable multi-hop broadcast protocols have been widely discussed recently. However, most of them use explicit acknowledgments and timeout retransmissions to provide reliability. The retransmission method incurs delays when a packet loss cannot be detected on time. Acknowledgment messages also increase the MAC layer contention time at each node. In order to provide a high reliability and low latency with a low overhead, we propose a mechanism which utilizes path diversity. In the proposed mechanism, a message is delivered through two different paths. By cooperation of these different paths, broadcast messages can be disseminated with a short delay and a high reliability compared with the acknowledgment based retransmission approach. Since the proposed mechanism does not use any explicit acknowledgment message, the message overhead is low. We evaluate the proposed mechanism using both theoretical analysis and computer simulations.

Efficient Broadcasting in VANETs Using Dynamic Backbone and Network Coding

Multihop data dissemination in vehicular ad hoc networks (VANETs) is very important for the realization of collision avoidance systems and many other interesting applications. However, designing an efficient data dissemination protocol for VANETs has been a challenging issue due to vehicle movements, limited wireless resources, and the lossy characteristics of wireless communication. In this paper, we propose a protocol that can provide a lightweight and reliable solution for data dissemination in VANETs. The protocol employs dynamically generated backbone vehicles to disseminate broadcast packets to reduce the MAC-layer contention time at each node while maintaining a high packet dissemination ratio by taking into account vehicle movement dynamics and the link quality between vehicles for the backbone selection. The protocol also uses network coding to reduce the protocol overhead and to improve the packet reception probability as compared with conventional approaches. We use theoretical analysis and computer simulations to show the advantage of the proposed protocol over other existing alternatives.

A broadcast path diversity mechanism for delay sensitive VANET safety applications

Reliable multi-hop broadcast protocols for vehicular ad hoc networks have been widely discussed recently. However, most of them use acknowledgement based retransmissions to provide reliability. The retransmission method incurs delays when a packet loss cannot be detected on time. Acknowledgement messages also increase the MAC layer contention time at each node. In this paper, we propose a mechanism to use path diversity to provide the reliability. In the proposed mechanism, a message is disseminated by two different paths. By cooperation of these two paths, broadcast messages can be disseminated with a short delay and a high reliability compared with acknowledgement based retransmission approach. The proposed mechanism does not use any explicit acknowledgement message. We evaluate the proposed mechanism using both theoretical analysis and computer simulations.

Toward Practical and Intelligent Routing in Vehicular Ad Hoc Networks

Apart from vehicle mobility, data rate (bit rate) and multihop data transmission efficiency (including route length) have a significant impact on the performance of a routing protocol for vehicular ad hoc networks (VANETs). Existing routing protocols do not seriously address all these issues and are not evaluated for a real VANET environment. Therefore, it is difficult for these protocols to attain a high performance and to work properly under various scenarios. In this paper, we first discuss the challenges of routing in VANETs based on the data acquired from real-world experiments and then propose a routing protocol that is able to learn the best transmission parameters by interacting with the environment. The protocol takes into account multiple metrics, specifically data transmission rate, vehicle movement, and route length. We use both real-world experiments and computer simulations to evaluate the proposed protocol.

Joint Fuzzy Relays and Network-Coding-Based Forwarding for Multihop Broadcasting in VANETs

In vehicular ad hoc networks (VANETs), due to the limited radio propagation range of wireless devices, many safety applications require a multihop broadcast protocol to disseminate traffic warning information. However, providing an efficient multi-hop forwarding of broadcast messages has been a challenging problem due to vehicle movement, limited wireless resources, and unstable signal strength. In this paper we propose a broadcast protocol that can provide a low message overhead and a high packet dissemination ratio. The proposed scheme uses a fuzzy logic algorithm to choose the next hop relay nodes and uses network coding to improve the packet dissemination ratio without increasing the message overhead. By using the fuzzy logic algorithm, the protocol can choose the best relay node by taking intervehicle distance, vehicle velocity, and link quality into account. Network coding is used to improve the packet reception ratio by utilizing the broadcast nature of wireless channels. We show the effectiveness of the proposed scheme by using both theoretical analysis and computer simulations.

Coded packets over lossy links: A redundancy-based mechanism for reliable and fast data collection in sensor networks

In wireless sensor networks (WSNs), many applications require a high degree of reliability with low delay. Due to the lossy nature of wireless channels, achieving reliable communication can be very challenging. The most commonly adopted approach for achieving reliability is the acknowledgment based retransmission mechanism; however, this approach is inefficient in terms of end-to-end delay especially when there are a large number of hops from a sensor to the sink node. In this paper, we propose a redundancy-based approach that achieves high reliability and low end-to-end delay. The proposed protocol employs a network coding-based approach to improve packet redundancy when a link is unreliable or there is a strict end-to-end delay requirement. The protocol adaptively changes the redundancy level according to the application requirements and link loss rate. The protocol can be implemented easily because modification of the application layer at the source node and destination node is the only mandatory requirement. We implement the proposed mechanism on a real testbed which consists of IRIS motes, and evaluate the performance of the proposed mechanism using real-world experiments, network simulations and theoretical analysis.

An experimental study of peer behavior in a pure P2P network

Abstract: Dynamic peer behavior in P2P networks has a large impact on the performance of the network because each peer acts simultaneously as a server and a client in an overlay network. However, peer behavior in pure P2P networks is not well known because there is no management system and the network size is large. We have proposed a measurement method to collect information efficiently, and a method of analyzing the peer behavior with or without file uploading for pure P2P file sharing networks. These methods have been applied to Winny, which is the most popular P2P file sharing application in Japan. The analysis results show that the network is composed of about 30% of peers observed in 24h, and 50% of peers contribute to the network as file uploaders. Selfish peers, which leave the network after downloading, are observed especially in the morning. The file uploading peers and the peers joining after midnight remain in the network for a long period. We also give mathematical fitting for the distribution of the peer lifetime and the frequency of joining the network. These results show that the distribution of lifetime does not have a heavy tail, and the behavior of peers joining the network is not a Poisson process.