Tomoya Kitani

UbiREAL: realistic smartspace simulator for systematic testing

In this paper, we propose a simulator for facilitating reliable and inexpensive development of ubiquitous applications where each application software controls a lot of information appliances based on the state of external environment, users contexts and preferences. The proposed simulator realistically reproduces behavior of application software on virtual devices in a virtual 3D space. For this purpose, the simulator provides functions to facilitate deployment of virtual devices in a 3D space, simulates communication among the devices from MAC level to application level, and reproduces the change of physical quantities (e.g., temperature) caused by devices (e.g., air conditioners). Also, we keep software portability between virtual devices and real devices. As the most prominent function of the simulator, we provide a systematic and visual testing method for testing whether a given application software satisfies specified requirements.

A Method for Sharing Traffic Jam Information using Inter-Vehicle Communication

In this paper, we propose a method for cars to autonomously and cooperatively collect traffic jam statistics to estimate arrival time to destination for each car using inter-vehicle communication. In the method, the target geographical region is divided into areas, and each car measures time to pass through each area. Traffic information is collected by exchanging information between cars using inter-vehicle communication. In order to improve accuracy of estimation, we introduce several mechanisms to avoid same data to be repeatedly counted. Since wireless bandwidth usable for exchanging statistics information is limited, the proposed method includes a mechanism to categorize data, and send important data prior to other data. In order to evaluate effectiveness of the proposed method, we implemented the method on a traffic simulator NETSTREAM developed by Toyota Central R&D Labs, conducted some experiments and confirmed that the method achieves practical performance in sharing traffic jam information using inter-vehicle communication

A Technique for Information Sharing using Inter-Vehicle Communication with Message Ferrying

In this paper, we propose a method to realize traffic information sharing among cars using inter-vehicle communication. When traffic information on a target area is retained by ordinary cars near the area, the information may be lost when the density of cars becomes low. In our method, we use the message ferrying technique together with the neighboring broadcast to mitigate this problem. We use buses which travel through regular routes as ferries. We let buses maintain the traffic information statistics in each area received from its neighboring cars. We implemented the proposed system, and conducted performance evaluation using traffic simulator NETSTREAM. As a result, we have confirmed that the proposed method can achieve better performance than using only neighboring broadcast.

A uniform airdrop deployment method for large-scale wireless sensor networks

The performance of wireless sensor networks in terms of coverage, connectivity, lifetime and robustness is greatly influenced by the initial physical placement of the sensor nodes. In this paper we propose a novel deployment method for sensor nodes, when a large number of nodes is distributed from the air in a monitoring region that is inaccessible from the ground. In our deployment method, each sensor node is equipped with a parachute and a device to switch between its two falling behaviours (gliding and falling) in the air. After being dropped from midair, sensor nodes stochastically coordinate their falling behaviour in order to distribute themselves uniformly in the monitoring region. In addition, each sensor node exchanges messages with neighbouring nodes while being airborne and it changes its falling behaviour according to the density of the neighbouring nodes in order to reduce non-uniform areas. Through simulation evaluations, we confirm that our proposal can achieve a high uniformity in the placement of the nodes compared to a traditional airdrop method.

A Method for Improving Data Delivery Efficiency in Delay Tolerant VANET with Scheduled Routes of Cars

In Vehicular Ad Hoc Networks (VANETs), delivering messages to a specific location is difficult due to the high mobility of vehicles. In this paper, we propose a method for efficient message delivery in VANETs utilizing the route information in car navigation systems. In the proposed method, each car periodically exchanges the information on its current position and scheduled route in the car navigation system with neighboring cars within radio range. By referring to the exchanged information, each car forwards messages to the neighboring car that will most closely approach the destination. Through simulations, we confirm that the proposed method achieves a better delivery rate with low bandwidth usage than a Geocast-based method and Epidemic routing.

Probabilistic data collection protocols for energy harvesting sensor networks

Energy harvesting has been studied as a candidate for powering next generation wireless sensor networks. The technologies that can harvest electric power from ambient energy sources include solar, vibration, heat and wind. However, sensor nodes powered by energy harvesting devices cannot always communicate with other nodes because the energy harvesting devices cannot provide a stable supply power. A node cannot know whether its neighboring nodes have enough energy to receive a data packet that it has transmitted. During the process of relaying the packet, each additional hop increases the overall probability of losing the packet. In this paper, we propose two data collection protocols for the energy harvesting wireless sensor networks called Probabilistic ReTransmission protocol (PRT) and PRT with Collision Consideration (PRT-CC). The idea is to derive the number of times to retransmit a packet based on the reception probability and the active intervals computed by the receivers themselves. In PRT-CC, each node computes the reception probability with packet collision consideration. The simulation results show that the proposed protocols achieve higher delivery ratio than the previous works (GR-DD and GR-DD-RT).

DAR: Distributed Adaptive Service Replication for MANETs

Mobile Ad Hoc Networks (MANETs) can be used to provide mobile users temporary infrastructure to use services such as database retrieval service when traditional infrastructure-based networks are unavailable in infrastructure-less situations (e.g. after a destructive disaster like an earthquake). The challenging task in such dynamic environments is how we can improve the service availability. An effective strategy is replicating a service at some nodes distributed across the network. However, service replication can considerably impact the system energy consumption. Since mobile devices have a limited amount of battery, a dynamic and efficient service replication is necessary to support such environments. In this paper, we propose a distributed service replication scheme for achieving high service availability with reasonable energy consumption for MANETs. The proposed method called Distributed Adaptive Service Replication (DAR) divides the whole network into disjoint zones of at most 2-hops in diameter and builds a dynamic replication mechanism which puts replicas only in zones with high service demand. Through simulations, we have confirmed that our approach can achieve higher service availability and lower energy consumption than an existing method.

A Configuration Method for Structured P2P Overlay Network Considering Delay Variations

P2P networks can achieve high scalability since they distribute service contents/resources to multiple nodes in the network. In a P2P network, it is necessary to search the resource location on the network when we use some contents/resources. Space filling curve is known as technique to map information of the multi-dimensional space such as the location information onto the one-dimensional space such as ID. In this paper, we propose a novel space filling curve for configuring structured P2P overlay network considering delay based on the geographic information of each node. By using the proposed space filling curve, we can convert geographic information of nodes into their ID (label) of P2P network. Through the numerical evaluation, we confirmed that the proposed curve is more suitable for handling hierarchical spread nodes than the conventional curves.

Automatic classification of motorcycle motion sensing data

Motorcycles are cost-efficient transportation but regarded as unsafe. To build safer motorcycle, the vehicle motion of motorcycles should be clarified. The motion depends on that of a rider much more than that of the body of a motorcycle, and thus motorcycle companies do not have enough motion data. Our research group has researched a sensing network with motorcycles and a vehicle-motion corpus of motorcycle. In this paper, we propose a method to attach an appropriate label to sensed data from the sensing network.

Probabilistic data collection protocols for energy harvesting wireless sensor networks

Energy harvesting from ambient energy sources including solar and vibration has been studied as a candidate for powering next generation wireless sensor networks. However, energy harvesting is unstable to supply a sensor node with energy, and a node cannot know whether its neighbouring nodes have enough energy to receive a data packet. In this paper, we propose two data collection protocols for energy harvesting wireless sensor networks called the Probabilistic ReTransmission protocol (PRT) and PRT with Collision Consideration (PRT-CC). The idea is to derive the appropriate number of times to retransmit a packet based on the reception probability and the active intervals computed by the receivers themselves while, in PRT-CC, each node computes the reception probability with packet collision consideration. The performance evaluation shows that the proposed protocols are able to achieve higher delivery ratio than the previous work, namely, Geographic Routing with Duplicate Detection (GR-DD) and GR-DD with Retransmission.