Akimitsu Kanzaki

Dynamic TDMA slot assignment in ad hoc networks

In this paper we propose a TDMA slot assignment protocol to improve the channel utilization, which controls the excessive increase of unassigned slots by changing the frame length dynamically. Our proposed protocol assigns one of the unassigned slots to a node which joins the network. If there are no unassigned slots available, our proposed protocol generates unassigned slots by depriving one of the multiple slots assigned to a node, or enlarging frame length of nodes which can cause collision with each other. Moreover, by setting frame length as a power of 2 slots, our proposed protocol provides the collision-free packet transmission among nodes with different frame length. The simulation results show that our proposed protocol improves the channel utilization dramatically as compared with the conventional protocols.

An adaptive TDMA slot assignment protocol in ad hoc sensor networks

Due to its ability to provide collision-free packet transmission regardless of the traffic load, TDMA (Time Division Multiple Access) has been applied in ad hoc sensor networks. We have previously proposed a TDMA slot assignment protocol that utilizes the channel bandwidth effectively in ad hoc sensor networks. However, in this protocol, the channel bandwidth cannot be fully utilized because the frame length across the whole network tends to increase. In this paper, we extend this protocol to further improve channel utilization. The extended protocol prevents the excessive increase of unassigned slots by minimizing each nodes frame length. Furthermore, we verify the effectiveness of our proposed protocols by simulation experiments. The results show that our extended protocol improves channel utilization dramatically in comparison with our previous protocol.

Overhearing-Based Data Transmission Reduction for Periodical Data Gathering in Wireless Sensor Networks

In this paper, we propose a novel energy-efficient data transmission reduction method for periodical data gathering in Wireless Sensor Networks (WSNs). Our method exploits overhearing, which is a typical characteristic of wireless communications. In our method, each node in a WSN autonomously determines whether its own reading is redundant or not by using the overheard packets transmitted by its neighbors. The redundancy of a reading is evaluated by a simple spatial interpolation using the readings of its neighbors. If the reading is determined as redundant, the node stops transmitting it. Furthermore, we present an evaluation based on simulation experiments with various parameters and show that our method suppresses data transmissions and reduces total energy consumption.

Consistency Management among Replicas Using a Quorum System in Ad Hoc Networks

Data replication is effective for improving data availability in ad hoc networks. In an environment where data updates occur, replicas of a data item may be inconsistent. To solve this problem, quorum based consistency management is a promising approach. To reduce communication overhead, it is better to make the number of mobile hosts in each quorum small. In this paper, we propose a consistency management method that constructs quorums with fewer mobile hosts.

An Effective Mobile Sensor Control Method for Sparse Sensor Networks

In this paper, we propose an effective mobile sensor control method, named DATFM (Data Acquisition and Transmission with Fixed and Mobile node) for sparse sensor networks. DATFM uses two types of sensor nodes, fixed node and mobile node. The data acquired by nodes are accumulated on a fixed node before being transferred to the sink node. In addition, DATFM transfers the accumulated data efficiently by constructing a communication route of multiple mobile nodes between fixed nodes. We also conduct simulation experiments to evaluate the performance of DATFM.

An efficient TDMA slot assignment protocol in mobile ad hoc networks

Because of its ability to provide the collision-free packet transmission regardless of the traffic load, TDMA has been applied effectively in ad hoc networks. Until now, assuming a stationary ad hoc network, a TDMA slot assignment protocol which achieves the high channel utilization has been proposed. In this paper, we extend the protocol to accomodate the dynamic topology change due to the movement of nodes. In our protocol, since each node autonomously detects a change in network topology and assigns a slot to itself, the high channel utilization in the previous protocol can be kept even when nodes in a network move. Furthermore, we verify the effectiveness of the protocol by simulation experiments. The results show that our protocol improves channel utilization in comparison to conventional protocols.

A route construction based on measured characteristics of radio propagation in wireless sensor networks

In wireless sensor networks, there are many constraints on electrical power and communication since sensor nodes have limited resources. Therefore, it is important to construct an effective communication route in terms of energy-efficiency and quality of communication. Many studies have been conducted to address this issue. In particular, controlling the transmission power of each node has been one of the hottest issues in recent years. Most conventional studies have assumed an environment in which radio signals transmitted by nodes propagate equally in all directions. However, this model cannot be applied to real environments due to several effects such as the presence of obstacles and antenna characteristics. In this paper, we propose a route construction method based on the measured characteristics of radio propagation in a real environment. Our method first measures the characteristics of radio propagation for all radio links. Second, the transmission power of each node and a communication route from the node to the sink node are determined based on the measured characteristics. In addition, we conduct experiments to verify that our methods can construct effective communication routes in terms of energy-efficiency and quality of communication.

X-Sensor: Wireless Sensor Network Testbed Integrating Multiple Networks

This chapter describes a wireless sensor network testbed, named XSensor, that integrates multiple sensor networks. X-Sensor manages multiple wireless sensor networks constructed at different sites, which can be accessed by remote users. This makes easy for users to conduct experiments in different environments. Moreover, X-Sensor provides real sensor data acquired by sensor nodes in each sensor network, which are useful for researchers working on research fields related to sensor data such as sensor data mining and analysis.

A Dynamic Cluster Construction Method Based on Query Characteristics in Peer-to-Peer Networks

To improve the efficiency of information retrieval in P2P networks, there have been many researches on categorizing data items and clustering peers. In almost all these researches, the number of categories and the policy of categorization are predetermined and static. However, users’ requirements for information retrieval dynamically change. This leads to undesired increase of network traffic. In this paper, we propose a dynamic cluster construction method based on query characteristics and a search method using dynamic cluster. Our method dynamically constructs clusters, when the access frequencies for certain data items increase. This approach can reduce the number of query messages for searching data items further than static clustering methods.

On a TDMA Slot Assignment Considering the Amount of Traffic in Wireless Sensor Networks

In this paper, we propose a TDMA slot assignment protocol that assigns slots to sensor nodes according to the skew of traffic load. Our protocol prevents the appearance of unassigned slots and utilize the channel effectively by adopting our previous slot assignment protocol that dynamically changes the frame length of each node. In addition, each node exchanges the information on traffic load with its neighbors and, if necessary, migrates assigned slots. Thus, our protocol can allocate the channel bandwidth effectively even when there is a skew of the traffic load. Furthermore, we verify the effectiveness of our protocol by simulation experiments.