Hiroaki Higaki

Navigation system based DTN routing in sparse vehicular networks

Various ad-hoc routing protocols have been proposed for wireless networks with dense distribution of wireless nodes. For support of multihop transmission in sparse wireless networks, some DTN (delay-tolerant network) routing have been proposed. However, it is difficult to get better tradeoff between communication overhead and reachability of data messages in DTN routing. This paper proposes a novel DTN routing protocol with help of satellite navigation system mounted on vehicles for vehicular ad-hoc networks (VANETs). By transmission of data messages along a driving route detected by the navigation system and recovery from the deviation due to next-hop detection failure, the proposed routing achieves high reachability though no copies of data messages are transmitted.

Extension of RH2SWL for Collision-Free Data Message Transmissions by Subsidiary Channel in Wide-Area Wireless Multihop Networks

For achieving higher end-to-end throughput of data messages in wireless multihop networks, collisions and contentions among wireless nodes in a transmission route are required to be avoided or reduced. Under an assumption that each wireless node communicates by using a single channel, collisions are avoided by RH2SWL since a transmission route consists of a sequence of hop-by-hop shortening wireless links. However, distance between a source and a destination wireless nodes connected by a sequence of hop-by-hop shortening wireless links is limited. Therefore, it is difficult for RH2SWL to be applied in wide-area networks. This paper proposes an extension of RH2SWL by introduction of an extended wireless link into a transmission route in which a subsidiary channel different from a usual channel used in each hop-by-hop shortening link is applied. Here, no collisions occur and connectivity is improved.

NeBuST: Low-latency congested sensor data transmission protocol

In wireless sensor networks, sensor data messages are transmitted to a sink node by using wireless multihop transmission with help of intermediate sensor nodes. In event-based sensor networks, no or few sensor data messages are transmitted in usual and burst sensor data messages are required to be transmitted when a sensor detects occurrence of a certain event. It may cause congestion along a multihop transmission route and result in lost messages by buffer-overflow and longer transmission delay. To solve this problem, we propose NeBuST protocol in which congested sensor data messages are buffered not only in the sensor nodes in the route but also in neighbor sensor nodes of the route. Simulation experiments show that the proposed protocol requires shorter transmission delay than the conventional data message buffering only in sensor nodes along the route.

Channel Assignment Protocol with Weaker Restrictions in Wireless Multihop Networks

In wireless multihop networks such as wireless ad-hoc networks, sensor networks and mesh networks, contentions and collisions reduce throughput of data message transmissions. For achieving contentionand collision-free networks, algorithms for assignment of one of multiple communication channels to each wireless communication link has been proposed. However, the ratio of successful channel assignment in the conventional algorithms is not so high due to too hard restrictions on channel assignment. This paper proposes a channel assignment algorithm with weaker restrictions where possible collisions at nodes out of wireless multihop transmission routes are allowed. Based on the novel algorithm, a backward-type channel assignment protocol is designed. Simulation results show that our protocol achieves higher assignment ratio than the conventional protocols with more than 6 communication channels in each wireless communication link.