Mirroring of network servers has been considered to be effective for load balancing. However, the cost of setting up new mirror servers is enormously high. In this paper, we propose a dynamic file allocation model with a simple mirroring function for handling significant changes of network traffic in the Internet. According to the load fluctuation, we can dynamically reallocate files using this model. We show that our model accomplishes satisfactory performance and reduces cost by adding a simple mirroring function to all existent servers instead of setting up mirror servers afresh.

In recent years, researchers have studied extensively about vehicle collision avoidance. The authors have developed Vehicular Collision Avoidance Support System (VCASS) based on IVC in order to prevent a vehicular collision beforehand. The system grasps the relative locations of vehicles by exchanging the GPS information in each vehicle. Then the system warns drivers if it detects some danger of collision. VCASS can drastically reduce the potential accidents of vehicular collisions. However, VCASS can not avoid collisions between vehicles and pedestrians, but avoid collisions just between vehicles. About 30% of fatal accidents by vehicles are happened with pedestrians in Japan. So it is necessary to develop a new system for pedestrians. This paper deals with collision avoidance between pedestrians and vehicles. There are two problems to develop such system. First it is necessary to reduce the power consumption of the pedestrian terminal, because pedestrian terminals have small-sized battery compared with vehicles. Second it is necessary to consider the movement characteristic of the pedestrian. In this paper, we propose a new Pedestrian-Vehicular Collision Avoidance Support System (P-VCASS) which extends VCASS. P-VCASS solves above two problems. We show the validity of the proposed system by experiments using some vehicles.

In this paper, we develop a VCASS substitution system (S-VCASS) using a personal mobile terminal in order to improve the effectiveness of VCASS in an environment comprising both VCASS and non-VCASS vehicles. We propose three new pedestrian state judgment algorithms that can be implemented on a personal mobile terminal for inter-vehicle communications. We evaluate the performances of the three proposed algorithms with real vehicles. Finally, we show that the proposed algorithms can recognize vehicles without VCASS.

In distributed network systems, it is one of the most important problems how to assign the files to servers in view of cost and delay. It is obvious that there is a trading-off relationship between costs and delays in these systems. In order to evaluate the optimization that the total cost is minimized subject to the total delay, we have presented the Optimal File Allocation Model as 0-1 integer programming, and have investigated the general characteristics in distributed systems. In this model, we have introduced many cost and delay parameters to evaluate the total cost and delay in the system more exactly. In constructing practical systems, it is necessary to investigate the weight and the contribution of each parameter to the total cost. It is very useful to show how to estimate cost and delay parameters on the basis of this analysis. In this paper, we analyze the sensitivity of these parameters and make clear the influence between principal parameters.

In wireless ATM networks, the condition of the transmission channel fluctuates significantly as a result of many causes such as multipath, shadow phasing, and so forth. Several schemes have been proposed to take care of transmission errors. Some schemes are suitable for favorable channel conditions, while others are more suitable for unfavorable channel conditions. Thus, using a fixed error control scheme regardless of channel conditions is destined to be inefficient. This paper presents a dynamic error control scheme that dynamically selects an appropriate error control scheme according to the conditions of the transmission channel. Using this method, we can decrease both errors and the overhead of redundancy.

Various recent intelligent transport system projects are promoting vehicle safety and efficient vehicular traffic control all over the world. One of ITS applications is a system that solves road traffic problems by using vehicular communications technology. Inter-vehicle communication (IVC) is the communications technology for vehicles to exchange moving vehicle information by wireless networks without any base stations. The Vehicular Ad-hoc Network (VANET) is expected to provide new applications for passengers of vehicles by enabling vehicles to communicate with each other via IVC as well as with roadside base stations via roadside-to-vehicle communications. However, when each vehicle transmits its own information to neighboring vehicles, the amount of information being transmitted increases significantly. To solve this problem, we present a novel real-time recognition method for vehicular traffic congestion via VANET with IVC. Vehicles collect the original GPS information of other vehicles by communicating with each other, and they create content that may be useful for drivers by analyzing that original information. The proposed method can reduce the information amount and deliver the analyzed contents to other vehicles efficiently. Computer simulation results show that the proposed method provides real-time information of vehicular accidents and traffic congestion to distant vehicles accurately.

A new transfer mode and a switching architecture which can support loss free and no delay jitter service class with shorter switching delay compared with "stop and go queueing scheme" is proposed. This scheme combines ATM scheme with hierarchical STM framing concept.

Recently, the border security systems attract attention as large-scale monitoring system in wireless sensor networks (WSNs). In the border security systems whose aim is the monitoring of illegal immigrants and the information management in long-period, it deploys a lot of sensor nodes that have the communication and sensing functions in the detection area. Hence, the border security systems are necessary to reduce the power consumption of the whole system in order to extend the system lifetime and accurately monitor the track of illegal immigrants. In this paper, we propose two effective barrier coverage construction methods by switch dynamically operation modes of sensor nodes to reduce the operating time of the sensing function that wastes a lot of power consumption. We carry out performance evaluations by computer simulations to show the effectiveness of two proposed methods and show that the proposed methods are suitable for the border security systems.

In this paper, we present a new design to support multicasting in an ATM switches, called the Singlecast Stuffed Multicast Advanced Processing (SSMAP) ATM switch, which can transmit multicast traffic effectively. The SSMAP ATM switch consists of two cell operation parts, a multicast operation part and a singlecast operation part. This structure is designed so as to increase the efficiency of packet forwarding by allowing singlecast cells to use the resources that remain unused during multicast traffic handling. Furthermore, we propose new multicast scheduling methods using the SSMAP ATM switch. We evaluate the characteristics of the SSMAP ATM switch and multicast scheduling methods by computer simulations, and demonstrate their validity.

The RFID tag system has received attention as an identification source. Each RFID tag is attached to some object. With the unique ID of the RFID tag, a user identifies the object provided with the RFID tag, and derives appropriate information about the object. One of important applications of the RFID technology is the position estimation of RFID tags. It can be very useful to acquire the location information concerning the RFID tags. It can be applied to navigation systems and positional detection systems for robots etc. In this paper, we propose a new position estimation method of RFID tags by using a probabilistic approach. In this method, mobile objects (person and robot, etc.) with RFID readers estimate the positions of RFID tags with multiple communication ranges. We show the effectiveness of the proposed method by computer simulations.

In recent years, there are many collision accidents between vehicles due to human errors. As one of countermeasures against the collision accidents, automotive radar systems have been supporting vehicle drivers. By the automotive radar mounted on the vehicle, it is possible to recognize the situation around the vehicle. The ranging with automotive infrared laser radar is very accurate, and able to understand the object existence in the observation around the vehicle. However, in order to grasp the situation around the vehicle, it is necessary to be aware of the attribute of the detected object. The information obtained by the automotive radar vehicle is only the direction and the distance of the object. Thus, the recognition of the attribute of the detected object is very difficult. In this paper, we propose a novel vehicle information acquisition method by using 2D reflector code. Through experiments, we show that the proposed method is able to detect 2D reflector code and is effective for vehicle information acquisition.

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.

In this paper, we consider optimal mirror allocation problems for the purpose of load balancing in network servers. We focus on constructing high-reliability networks and propose the optimal mirror allocation model such that the system reliability is maximized subject to costs and delays, in view of the trade-off between the reliability and cost. This optimization model is capable of dealing with various kinds of network topologies, although for simplicity, we assume the read-only situation. We formulate this optimization problem into a 0-1 integer programming model, and we use an approximate method for numerical analysis in order to analyze more large-scale systems. Our objective is to find the optimal mirror allocation by solving this model, and to show quantitatively the general characteristics of the load balancing and the improvement of the system reliability by the distributed mirror allocation.

CDMA is considered a suitable access control for wireless multimedia communication systems. In this paper, we present an access scheme for packet-typed wireless networks, called PRMA/URN (Packet Reservation Multiple Access/URN) for the CDMA environment. This protocol combines URN algorithm with PRMA, instead of slotted-ALOHA. Also, we introduce enhanced access control into PRMA/URN for effective transmission of multimedia information, i.e. voice and data information. The enhanced access control has two characteristics. First, voice mobile terminals have priority in the initial access. Second, data mobile terminals can transmit packets continuously if necessary. We carry out the performance comparisons for CDMA environments between PRMA, PRMA/URN and PRMA/URN with enhanced access control, and show numerically the effectiveness of PRMA/URN with enhanced access control.

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.

Multicast routing problem is one of the essential problems for supporting multicast and broadcast communication service which is the most important service of the multimedia information networks. Multicast routing is the problem of finding out an adequate path which connects one source node and more than one destination node, i.e. a tree shaped path. In packet type networks, a packet for multicast communication should go through the tree shaped path as making its copies at a branching node for efficient use of network resources. However, concentration of packet copy operations at a particular node leads to performance degradation of other calls which go through this node. In this paper we propose two multicast routing algorithms which distribute packet copy operations through whole nodes in the multicast path; a link added type algorithm and a loop constructed type algorithm. Both algorithms, at first, find out an approximate solution for minimum cost path, and avoid concentration of packet copy operation at a little sacrifice of total cost in the path. Computer simulation results show that these algorithms can decrease the burden of packet copy operation per a node at the sacrifice of increase in average distance (cost) of a source-destination pair but the sacrifice of total cost is very small.

Inter-Vehicle Communication (IVC) is one of the most important technologies to realize advanced Intelligent Transport Systems (ITS). We extensively apply the IVC technology to the communications between pedestrians and vehicles. We call this kind of communications VPEC (Vehicle-PEdestrian Communications). The objective of this paper is to present an effective control scheme for VPEC and to evaluate the performance of proposed scheme by experiments. We deal with direct communications between pedestrians and vehicles. Due to the battery shortage of pedestrians' terminals (p-node), we have presented a reflect-transmission scheme. In this paper, we propose a new access protocol for reflect-transmission scheme, and show its validity by various experiments with several vehicles.

The RFID (Radio Frequency IDentification) tag technology is expected as a tool of localization. By the localization of RFID tags, a mobile robot which installs in RFID readers can recognize surrounding environments. In addition, RFID tags can be applied to a navigation system for walkers. In this paper, we propose an adaptive likelihood distribution scheme for the localization of RFID tags. This method adjusts the likelihood distribution depending on the signal intensity from RFID tags. We carry out the performance evaluation of estimated position error by both computer simulations and implemental experiments. We show that the proposed system is more effective than the conventional system.

In this paper, we present an access scheme for packet-typed wireless networks, called DQRUMA/PAR (Distributed-Queueing Request Update Multiple Access with Periodically Automatic Reservation), which can transmit multimedia traffic efficiently. Here, we deal with three kinds of traffic i. e. voice, data and still picture. DQRUMA/PAR introduces the transmission scheme that mobile stations for voice communications reserve the transmission capacity periodically during their talkspurts. The transmission control process of DQRUMA/PAR will become easier than the one of DQRUMA, and the delay characteristic of voice is improved. Furthermore, we study two enforced protocols on DQRUMA/PAR. One is the more enforced protocol for voice communications. We call this as Voice Enforced mode (VE mode) on DQRUMA/PAR. The other is the more enforced protocol for data communications. We call this as Data Enforced mode (DE mode) on DQRUMA/PAR. The transmission delay of voice will become reduced significantly by introducing VE mode. On the other hand, the transmission delay characteristic of data will be improved by introducing DE mode. We carry out the performance comparisons of pure DQRUMA/PAR with PRMA and DQRUMA and show the considerable improvement of the protocol numerically. Next we make the performance comparisons between pure DQRUMA/PAR and two enforced modes on DQRUMA/PAR and show the considerable improvements of these enforced protocols, respectively.

RFID (Radio Frequency Identification) technology is expected to be used as a localization tool. By the localization of RFID tags, a mobile robot equipped with an RFID reader can recognize the surrounding environment. In this paper, we propose a novel effective scheme called the communication range recognition (CRR) scheme for localizing RFID tags. In this scheme, an RFID reader determines the boundaries of the communication range when it is appropriately positioned by the robot. We evaluate the estimated position accuracy through numerous experiments. We show that the moving distance of the RFID reader in the proposed scheme is lower than that in conventional schemes.