Shinya Kitajima

A Mobile Sensor Control Method Considering Node Failures in Sparse Sensor Network

Advances in wireless communication technology have led to an increasing interest in mobile sensor networks.In our previous work, we proposed a method that controls the movement of sensor nodes by using push-based broadcast and communication among nodes.In this method, nodes autonomously move based on the broadcast information on where they can communicate with the sink,and they construct a temporal network to deliver their sensor readings to the sink.However, this method has two problems.First, it cannot sufficiently reduce the moving distances of nodes.Seconds, this method assumes an ideal environment in which node failures do not occur, whereas node failures do occur in real environments.In this paper, we extend our previous method to solve these problems. We also show the results of simulation experiments regarding a performance evaluation of the extended method.

A Query Processing Mechanism Based on the Broadcast Queue for Broadcast Database Systems

In recent years, there has been an increasing interest in the broadcast database system, where the server periodically broadcasts contents of a database to mobile clients such as PDAs. There are three query processing methods in the broadcast database system: (i) the server processes a query and then broadcasts the query result to the client; (ii) the client stores all data that are necessary in processing the query and then processes it locally; and (iii) the server and the client collaborate in processing the query. Since the performance of each method changes according to the situation, such as the interval of query generation and the size of query results, it is difficult to decide the optimal method among them statically. In this paper, we propose a new query processing method which dynamically changes the order of queries submitted in the queue at the server and also changes processing methods for the queries according to the deadline of queries and the system situation. Our method not only improves the response time but also increases the success rate of query processing compared with the traditional methods.

A Broadcast-Based Data Gathering Method Considering Energy Consumption for Sensor Networks

In recent years, there has been an increasing interest in sensor networks, in which sensor nodes such as temperature or humidity sensors communicate with each other for environmental monitoring and so on. In sensor networks, it is important to reduce the energy consumption, since sensor nodes have limits in battery. Most researches achieve this by reducing sensor amount of transmitted data. However, there is a problem that the amount of transmitted data become large and their energy consumption becomes high when there are a lot of nodes in the sensing area. To solve the problem, we previously proposed a data gathering method. In this method, the data sink estimates the data value of nodes, broadcasts the estimated values, and then, sensor nodes whose observed values are largely different from the estimated values send the data. However, this method has a problem that it cannot sufficiently reduce the energy consumption. In this paper, we propose a new broadcast-based data gathering method. In this method, the data sink reduces the nodes which send their observed values when the reliability of gathered values by the data sink is high.

A Query Processing Method Considering the Characteristic of Energy Consumption for Broadcast Database Systems

In recent years, there has been an increasing interest in a broadcast database system where the server periodically broadcasts contents of a database to mobile clients such as PDAs and smart phones. There are three query processing methods in the broadcast database system. Generally, mobile clients have limits in energy consumption, i.e., battery,and each of the three methods consumes different amount of energy for query processing. In this paper, we propose a new method which dynamically chooses one of the three query processing methods considering energy consumption.

A Query Processing Method Considering Query Frequency for Broadcast Database Systems

In recent years, there has been an increasing interest in broadcast database systems, where the server periodically broadcasts contents of a database to mobile clients such as PDAs. There are three query processing methods in the broadcast database system: (i) the server processes a query and then broadcasts the query result to the client; (ii) the client stores all data that are necessary in processing the query and then processes it locally; and (iii) the server and the client collaborate in processing the query. Since the performance of each method changes according to the system situation, such as query frequency, it is difficult to decide the optimal method among them statically. In this paper, we propose a new query processing method which dynamically changes the query processing method based on query frequency. This method improves not only the response time but also the success rate of query processing compared with the traditional methods.

On query processing considering energy consumption for broadcast database systems

In recent years, there has been an increasing interest in the broadcast database system where the server periodically broadcasts contents in a database to mobile clients such as portable computers and PDAs. There are three query processing methods in the broadcast database system, while each method consumes different amount of power for query processing. In this paper, we propose a new query processing method which dynamically chooses an appropriate method among the three query processing methods by considering energy consumption.