Tadayuki Fukuhara

Broadcast methods for inter-vehicle communications system

This paper presents novel broadcast methods for an inter-vehicle communications system for ITS. During inter-vehicle communications, it is essential that emergency information be broadcast to surrounding vehicles. Emergency information such as emergency-vehicle-approach information and traffic accident information are needed by vehicles in a particular area. By limiting the broadcast direction, the proposed methods can provide broadcasts to a particular area and avoid mistakenly notifying other areas where the information is not needed. We developed a simulation and experimental system for the proposed method and confirmed that the information is broadcast to the desired area.

Channel occupancy estimation method for Wireless LAN

Channel occupancy is key information to realize efficient operation of the wireless system. Channel occupancy can be defined as the time occupancy ratio in the case of Wireless LAN (WLAN). We propose a novel passive method to estimate the time occupancy ratio of WLAN. The proposed method produces greater improvement in estimation accuracy compared with that of conventional methods. In this paper, we introduce the definition of the time occupancy ratio as the utilization index of a WLAN radio resource. Then, details of the proposal are introduced. Finally, the excellent evaluation results executed on an experimental system are introduced even when many loss packets exist.

Novel multiple path routing technology for multi-hop wireless networks

The novel routing method proposed enables simultaneous utilisation of multiple paths without them interfering with each other, and improves the system throughput of multi-hop wireless networks between base station (BS) and mobile users. The basic concept is that the BS searches and selects the secondary multi-hop path that is located out of the coverage of the primarily selected multi-hop path derived by the conventional AODV scheme. Simulation results show that the proposed scheme improves the system capacity of the conventional multi-hop wireless network.

Downlink Link Aggregation Performance with Delay Adjustment Capability in Multi-Radio Access System

Heterogeneous radio network which efficiently utilizes the resources of multi-radio access systems is one of promising approaches for flexible, reliable and high-capacity communication. Regarding the cooperative controlling functionality in the heterogeneous system, two schemes are considered to be applicable to the efficient usage of multi-radio systems. One is a link selection and the other is a link aggregation which bundles multi-radio access systems. In this paper, the link aggregation is focused and its improvement of the Transmission Control Protocol (TCP) transmission performance over the aggregated link is discussed. The key function of the aggregation is a delay adjustment capability, which compensates the time delay difference among multiple links by addition of the time delay. The performance characteristics are measured by the experimental testbed including LTE, WiMAX and Wi-Fi. The throughput improvement provided by the link aggregation and the effect of the packet re-transmission caused by the link aggregation are addressed.

User-Centric Seamless Handover Scheme for Realtime Applications

We bring a new perspective on a vertical handover scheme, a user-centric seamless handover, toward a next generation network where heterogeneous network systems converge. The proposed scheme allows us to provide users with the optimal service quality for real-time applications in respective network systems, as well as sustaining on-going sessions. Firstly we propose SIP-based bi-casting technology using a Handover Assistant Server to provide optimal service quality in respective network systems and avoid packet loss during handover. The delay difference absorption method is also proposed to adjust the service quality smoothly to the newly connected network. Evaluation results show that the scheme works well for the handover between cellular and high speed wireless access via the implementation of a prototype system.