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).

For accident prevention at intersections, it is useful for drivers to grasp the position of vehicles in blind spots. This can be achieved without infrastructure if some vehicles passing near the intersection capture and share live video of the intersection through inter-vehicle communications. However, such video streaming requires a congestion control mechanism. In this paper, aiming to let a driver grasp the situation at an intersection, we propose a method to select vehicles that send a video in order to generate a live bird's-eye-view video of the intersection. In our method, each vehicle at an intersection exchanges information with others, such as the sub-areas of the intersection it captures, the quality of its video, and its position and speed. Based on the exchanged information, each vehicle autonomously judges whether it should send its video or not. Through simulation with a QualNet simulator, we confirm that our method achieves a good video arrival rate and video quality sufficient for practical use.

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.

In this paper, we focus on the problem of implementing a periodic concurrent system with timing constraints into multi-context dynamically reconfigurable processors (DRP). A concurrent system has multiple tasks that can be executed in parallel. Moreover, some tasks in a specific set of processes might be required to synchronize each other. We propose a method for assigning tasks into a multi-context DRP such that timing constraints of the system are satisfied and the size of the program area required on each context for implementing the given system is minimized. We formulate the problem as an ILP problem and propose a heuristic algorithm for solving the ILP problem efficiently. Experimental results and a case study using ubiquitous sensor devices are given.

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.

In this paper, we propose a method which efficiently collects, retains and propagates traffic information using inter- vehicle communication with "message ferrying" technique used in vehicular ad hoc network (VANET). In the proposed method, we use buses as message ferries which travel along regular routes. In order to improve information propagation efficiency in low- density areas, buses collect as much traffic information as possible from cars in their proximity, and periodically disseminate the collected information to neighboring cars. We have implemented the proposed system on the traffic simulator NETSTREAM and compared information propagation efficiency between our proposed method and a method which uses inter-vehicle communication among only ordinary cars. In the simulation, the proposed method improved the efficiency up to 50%.

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.

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

In this paper, we propose a flexible and high-reliable HW/SW co-design method for real-time systems consisting of multiple functional modules using general purpose components such as DSP, CPU and memory. In our method, we specify a system as a parallel composition of concurrent periodic EFSMs with timing constraints. As communication primitives among EFSMs, multi-way synchronization mechanism can be specified. Here, we propose a technique for efficient development of real-time embedded systems considering both reliability and cost-performance. For the purpose, using a parametric model checking technique, we derive a parameter condition which must hold for the system to proceed without deadlocks and satisfy given timing constraints. Based on the derived parameter condition and cost-performance characteristic of available components, an appropriate combination of components is automatically selected so that the total cost is minimized. We have developed a design support tool based on the proposed technique. By applying our method to development of a basic functionality of a cellular phone, we could decide which functional modules should be implemented as dedicated HW units or on-chip-CPUs' software, and select suitable DSPs and memories with low costs.