Yosuke Tanigawa

Fair Routing for Overlapped Cooperative Heterogeneous Wireless Sensor Networks

In recent years, as wireless sensor networks (WSNs) are widely diffused, multiple overlapping WSNs constructed on the same area become more common. In such a situation, their lifetime is expected to be extended by cooperative packet forwarding. Although some researchers have studied about cooperation in multiple WSNs, most of them do not consider the heterogeneity in the characteristics of each WSN such as battery capacity, operation start time, the number of nodes, nodes locations, energy consumption, packet size and/or data transmission timing, and so on. In a heterogeneous environment, naive lifetime improvement with cooperation may not be fair. In this paper, we propose a fair cooperative routing method for heterogeneous overlapped WSNs. It introduces an energy pool to maintain the total amount of energy consumption by cooperative forwarding. The energy pool plays a role of broker for fair cooperation. Finally, simulation results show the excellent performance of the proposed method.

Delay-Sensitive Retransmission Method Based on Network Coding in IEEE 802.11 Wireless LANs

Recently, network coding (NC) has been popularly applied to wireless networks in order to improve channel utilization. In wireless LANs, when NC is applied to packet retransmission, a base station can simultaneously retransmit multiple packets destined to different wireless stations for a single retransmission trial. On the other hand, NC creates additional packet delay at both base station and wireless stations, and hence, packet transfer delay may increase seriously. However, existing NC-based retransmission methods do not consider this additional delay explicitly. In addition, when the number of flows is small, NC exhibits less benefits because the chances of NC-based retransmission are highly reduced. Therefore, in this paper, we propose a novel NC-based retransmission method in order to improve packet transfer delay and jitter of received packets. Moreover, to achieve further improvement of delay, jitter and retransmission efficiency, we propose a retransmission method in which NC-based retransmission cooperates with the typical ARQ method. We overcome the disadvantage of NC-based retransmission by combining with ARQ cooperatively. Finally, we show the effectiveness of the proposed methods by extensive computer simulation.

Active breadcrumbs: Aggressive distribution method of in-network guidance information for content-oriented networks

Lately, access loads on servers and network traffic are increasing due to larger content-size and higher request-frequency in content distribution networks. Breadcrumbs (an architecture with guidance information for locating a content cache) is designed to reduce server-loads and to form content oriented network autonomously in cooperation with cached contents. We also proposed Breadcrumbs+ which solves BCs problem that queries visit the same routers repeatedly with forming a loop of routing. However, Breadcrumbs itself still has a technical issue that some queries potentially traverse longer hops compared to conventional approach. In addition, Breadcrumbs takes only a passive approach; a query is routed by a trail of BCs only when the query happens to encounter a corresponding BC. This indicates that Breadcrumbs has a space to enhance its capability. We expect that active and adaptive control of BC improves user experience. In this paper, we propose Active Breadcrumbs which provides higher cache utilization through active spreading guidance information around cache-nodes. Finally, we show the effectiveness of Active Breadcrumbs in terms of traversing content/query hops and server utilization through the extensive computer simulation.

Selective retransmission with network coding based on restricted block ACK information in wireless LAN multicast

Recently, multicast delivery of multimedia data via wireless LAN is increasing. Though IEEE 802.11 lacks the mechanism to recover packet loss in multicast, network coding (NC) has demonstrated its potential to retransmit lost packets efficiently. However, in existing NC methods, transmission delay becomes worse as the number of receiver stations increases because lost packets are continuously retransmitted until all stations receive them. In transmission of multimedia data, especially, transmission delay should be minimized. Therefore, we decrease transmission delay and improve its scalability for the number of receiver stations, at the expense of small packet loss acceptable for multimedia data.

Integration Method between Localization and Routing in Underwater Sensor Network

These days, the demand on searching underwater area by using underwater sensor network becomes higher. However, we cannot apply terrestrial network protocols directly for this challenge because of the high attenuation and absorption of water that affect radio and optical waves. In underwater environment, especially, it is important to save redundant control messages required to establish and maintain the network at maximum. In this paper, we propose an integration method between localization and routing which were discussed separately so far by simply extending control packets exchanged for localization. The target of this work is efficient setup of the network. Finally, we show the effectiveness of the proposed method by computer simulation.

Breadcrumbs+: Some Extensions of Naive Breadcrumbs for In-network Guidance in Content Centric Networks

For several years, in content distribution networks, access loads at servers are greatly increasing due to larger contents. Breadcrumbs(guidance information for the location of a content cache) have been designed for reducing server loads and forming content oriented network autonomously in cooperation with cached contents. However, it has a problem that some queries cannot reach the intended content in a particular situation. In this paper, we first figure out the cause of the problem. And then, we propose the extended method of Breadcrumbs, named Breadcrumbs+, to solve the problem, remaining its naive property for high scalability i.e. excluding stateful management and control. Finally, we show the effectiveness of the proposed method by extensive computer simulation.

A study on power saving using RTS/CTS handshake and burst transmission in wireless LAN

Recently, buttery-powered portable devices, which can use wireless LAN (WLAN), such as smart phones and tablet computers, are increasing. However, these devices consume more energy when using WLAN interfaces, and the battery lifetime is shorten. In order to reduce the power consumption of wireless stations, IEEE 802.11 specifies PSM (Power Saving Mode). However, PSM cannot save the energy optimally and it increases the transfer delay of packets severely. In this paper, to reduce the power consumption and suppress the transfer delay, we propose a power saving method using RTS/CTS handshake and burst transmission. Wireless stations save energy by sleeping for NAV (Network Allocation Vector) duration. In addition, we extend NAV duration with burst transmission. The number of packets transmitted per burst is decided so that the acceptable transfer delay of each packet is preserved. Finally, we show the effectiveness of the proposed method by computer simulation.

A Congestion Control Method for Multiple Services on Shared M2M Network

In this paper, we propose a congestion control method for low-cost M2M devices in wireless multi-hop networks. By adding the packet priority to each packet and changing it dynamically at intermediate devices, this method considers the requested quality level for each service. Finally simulation results show the excellent performance of the proposed method.

Robust data gathering method using controlled mobility in underwater sensor network

These days, underwater exploration demand is increasing in the field of industry, science, military, and so on. Hence, Underwater Sensor Network to collect data by scattering sensors in water has been attracted attention. However, there are various problems specific to underwater environments including the communication medium. In this paper, we focus on some problems on broken or degrading link between two neighboring nodes moving away from each other along with water current. To recover such links, we propose to introduce and control mobile nodes to relay communication between such two nodes. Existing studies dealing with the controlled mobility focused on the movement from the sea bed towards the water surface in order to avoid broken links caused by a shadow zone. On the other hand, the proposed method recovers broken and degrading links caused by movement of sensors by the water flow. Different from exiting works, limited number of smart mobile nodes move in any directions. In addition, because the cost of node movement in UWSN is higher than that of terrestrial network, this method also aims at reducing the movement distance of mobile nodes. Furthermore, the proposed method can measure and deal with the link disconnection proactively because the movement of mobile nodes is controlled while grasping the network condition. Finally, we show the effectiveness of the proposed method by computer simulation.

A cooperative routing method with shared nodes for overlapping wireless sensor networks

In a wireless sensor network (WSN), one of the most important challenges is extending network lifetime because it is difficult to replace sensor nodes and recharge their batteries. In a WSN, nodes around a sink tend to die earlier than other nodes because these nodes have to transmit and relay more packets. To overcome this problem, many load-balancing methods were proposed. By the way, in recent years, two or more overlapping WSNs have been constructed in the same geographic area. In this situation, the overlapping WSNs are expected to extend their lifetime by cooperative packet forwarding. In this paper, we introduce shared nodes with multichannel communication capability as interchange points among respective WSN planes. With these shared nodes, we propose a novel cooperative routing method for WSNs to balance each others load. Finally, we show the effectiveness of the proposed method by simulation experiments.