Hiromi Okada

Development of vehicular-collision avoidance support system by inter-vehicle communications - VCASS

In order to achieve a safe automotive society, it is necessary to develop an on-board intelligent system with inter-vehicle communications (IVC). We want to avoid vehicle collisions under most situations, such as intersections, highways, and blind corners, by using IVC technology through wireless ad hoc networks. The paper describes a vehicular collision avoidance support system (VCASS), and shows its performance by various experiments with two real vehicles. We have installed personal computers, telecommunication equipment, and GPS in the vehicles. A vehicle exchanges location information and velocity vectors with the other by a UDP broadcast, and calculates the relative position/speed. Vehicles warn the drivers of the possibility of collision. We verify the validity and effectiveness of VCASS by experiments.

Vehicular-Collision Avoidance Support System (VCASS) by Inter-Vehicle Communications for Advanced ITS

In advanced ITS, on-board intelligent systems by the Inter-Vehicle Communications (IVC) is essential technology to achieve a safe automotive society. We aim to avoid the vehicular collisions under almost all situations such as intersections, highways, and blind corners by using IVC technology through wireless ad hoc networks. The objectives of this paper are to develop Vehicular Collision Avoidance Support System (VCASS), and to show its performance by various experiments with two real vehicles. We have installed personal computers, telecommunication equipments, and GPS in two vehicles. In this system, the vehicles exchange the location information and the velocity vectors by the UDP broadcast with each other, and calculate the relative position/speed. The vehicles make the warning for drivers with the possibility of the collision. We verify the validity and the effectiveness of VCASS by the experiments.

An effective BECN /CRN typed deflection routing for QoS guaranteed optical burst switching

In recent years, WDM networks have received much attention as the Internet backbone networks because of the explosive growth of the Internet IP-based traffic. The optical burst switching (OBS) has been proposed as an effective optical switching technology in the WDM networks (C. Qiao and M. Yoo, 1999). OBS has the advantages in 1) the high usage rate of the bandwidth, and 2) no necessity of optical buffer. However OBS has the burst-contention problem in the networks. The deflection routing is proposed as one of means to solve this problem. In this paper, we propose a new routing method of using deflection routing. In addition, we propose a QoS/CoS control method using a new routing algorithm. Finally, we show the variety of the proposed methods by computer simulations.

Interference-aware MAC scheduling and SAR policies for Bluetooth scatternets

Bluetooth utilizes fast frequency hopping to mitigate interference from other wireless devices and other Bluetooth piconets that share the same frequency range. However, it still can not avoid the interference between piconets entirely. In our simulation, we observed that the inter-piconet interference can significantly degrade the system throughput by more than 30%. The system throughput within a piconet can be improved by a proper arrangement of the segmentation/reassembling (SAR) policy and a good selection of MAC scheduling protocols. Many SAR policies and MAC scheduling protocols were proposed, but none of them takes the inter-piconet interference into consideration. In this paper, we study the impact of the interference on the performance of TCP traffic over a Bluetooth scatternet with multiple overlapping piconets. To alleviate the impact, we propose interference-aware SAR policies as well as the interference-aware MAC scheduling protocols. The simulation results show that our schemes help reduce the impact of the inter-piconet interference by more than 50%.

A Cost-Effective Dynamic Content Migration Method in CDNs

Content Distribution Networks (CDNs) are highly advanced architectures for networks on the Internet, providing low latency, scalability, fault tolerance, and load balancing. One of the most important issues to realize these advantages of CDNs is dynamic content allocation to deal with temporal load fluctuation, which provides mirroring of content files in order to distribute user accesses. Since user accesses for content files change over time, the content files need to be reallocated appropriately. In this paper, we propose a cost-effective content migration method called the Step-by-Step (SxS) Migration Algorithm for CDNs, which can dynamically relocate content files while reducing transmission cost. We show that our method maintains sufficient performance while reducing cost in comparison to the conventional shortest-path migration method. Furthermore, we present six life cycle models of content to consider realistic traffic patterns in our simulation experiments. Finally, we evaluate the effectiveness of our SxS Migration Algorithm for dynamic content reconfiguration across time.

Effective Flow-rate Control for the Deflection Routing based Optical Burst Switching Networks

Optical burst switching (OBS) has been proposed to realize the next generation Internet on the wavelength division multiplexing (WDM) network technology. In OBS, the burst contention is the major problem. The deflection routing has been designed for resolving this problem. However the deflection routing cannot prevent the burst contention as the network load becomes high. In this paper, we show that a flow-rate control is essential for OBS. We propose leaky bucket deflection method (LB Deflection method). In LB deflection method, edge nodes which generate data bursts carry out a flow-rate control based on leaky bucket method In order to verify the effectiveness of a flow-rate control in OBS, we show that LB Deflection method improves the network utilization and reduces the burst loss probability through computer simulation

Accuracy Improvement of Vehicular Collision Avoidance Support System (VCASS) for the next generation ITS

In recent years, researches and developments on ITS are carried out to solve many problems in road traffic. IVC (inter-vehicular communications) is the key technology to realize the next generation ITS (Tokuda et al., 2002 and Morioka et al., 2000). Vehicles install telecommunication equipments, and exchange information directly with each other. The authors have developed vehicular collision avoidance support system (VCASS) based on IVC in order to prevent a vehicular accident beforehand. The system grasps the relative location of vehicles by exchanging the GPS information in each vehicle. Then the system warns drivers if there is a danger of collision. In this paper we propose two schemes in order to improve the accuracy of VCASS. We evaluate the performance of conventional collision judgment algorithm and the proposal scheme for VCASS. We have verified the effectiveness of the new VCASS in typical road environments.

Effective reflect-transmission schemes for vehicle-pedestrian communications (VPEC)

Inter-vehicle communications (IVC) is one of the most important technologies for realizing advanced intelligent transport systems (ITS). We deal with Vehicle-PEdestrian Communications (VPEC) as communication between vehicles and pedestrians. The objective of VPEC is to protect pedestrians from traffic accidents. In VPEC without any controls, pedestrians (p-nodes) transmit many packets to vehicles (v-nodes) to provide the position information of p-nodes. But, the battery capacity of p-nodes is small. It is necessary to suppress the transmission of p-nodes to obtain proper information exchanges. We present effective reflect-transmission schemes which can reduce needless transmissions from p-nodes on VPEC. In addition, we present silent control protocol, mask control protocol and distance-based priority control protocol as more effective protocols for the reflect-transmission scheme. The proposed protocols can operate the reflect-transmission scheme more efficiently. Further, we have carried out a VPEC experiment to verify the control behavior of VPEC. We outline the experiments and show some results obtained.

A feedback-based contention resolution mechanism for slotted optical burst switching

Optical burst switching (OBS) has been proposed for an effective optical switching technology of WDM networks in broadband Internets. OBS has the advantages, i.e. 1) the high usage rate of the bandwidth and 2) no necessity of optical buffer. However, OBS has the burst-contention problem in control packet phase, and faces to the reduction of the network performance. Recently, slotted OBS has been proposed. The basic performance of slotted OBS is superior to the original OBS. However, slotted OBS itself cannot overcome the burst-contention problem, either. In this paper, we will adapt BECN/CRN typed deflection routing to slotted OBS to obtain the large improvement of the optical network performance. We also present two new schemes for slotted OBS to improve the burst contention problem, i.e. a) enforced waiting control and b) scheduling.

INTERFERENCE-MITIGATING MAC SCHEDULING AND SAR POLICIES FOR BLUETOOTH SCATTERNETS

Bluetooth utilizes fast frequency hopping to mitigate interference from other wireless devices and other Bluetooth piconets that share the same frequency range. However, it still cannot avoid the interference between piconets entirely. In our simulation, we observed that the inter-piconet interference can significantly degrade the system throughput by more than 10%. The system throughput within a piconet can be improved by a proper arrangement of the segmentation/reassembling (SAR) policy and a good selection of MAC scheduling protocols. Many SAR policies and MAC scheduling protocols were proposed, but none of them takes the inter-piconet interference into consideration. In this paper, we study the impact of the interference on the performance of TCP traffic over a Bluetooth scatternet with multiple overlapping piconets. To alleviate the impact, we propose interference-aware SAR policies as well as the interference-aware MAC scheduling protocols. The simulation results show that our schemes help reduce the impact of the inter-piconet interference by more than 15%.