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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.

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.

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.

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.

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.

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.

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 recent years, transportation convenience is improved significantly by the spread of the automobile. However, traffic violation vehicles passing on the signal, hit-and-run, etc. are increasing with the increase of vehicles. To track a violation vehicle, recognition systems of the license plate using the image processing technology and cameras have been developed. However this system becomes expensive and complicated. To solve these problems, we have proposed a recognition method of the vehicle code using infrared laser radar. We set up a one-dimensional code created by reflectors on the vehicle, and acquire the vehicle information by reading the vehicle code by infrared laser radar. It can be constructed inexpensive system by using infrared laser radar. However, there is a problem that the number of code patterns is small, so the system cannot accommodate too many vehicles. In this paper, we propose a new code recognition method using time-sequence processing for infrared laser radar. We create a two-dimensional code by setting different type reflectors on vertical positions. Thereby we increase the number of code patterns. Through experiments, we demonstrate the effectiveness of the proposed method.

We have proposed a simple vehicular information acquisition scheme using infrared radar and reflector code in order to recognize vehicle information with low cost. However, since the size of the reflector code is so large and the number of code patterns is not so large, it is necessary to reduce the size and increase the patterns in order to be attached with vehicles. So we propose a new scheme using subdivided reflector code.

The quasi-synchronous transfer mode (Q-STM) method realizes cell-loss free and intranetwork delay jitter-free transmission on asynchronous transfer mode network, by allocating transmitted cell positions. In this paper, some design issues of the Q-STM method are considered and the applicability of the Q-STM method is investigated. First, the algorithms of the call setup procedure for Q-STM are compared. The effect of the number of subframes (NS) is investigated, and the most efficient NS in an assumed environment is obtained. Moreover, the QOS of ATM service class and processing time of a call setup are evaluated. Through these evaluations, we show guidelines for implementing the Q-STM and the applicability of the Q-STM.

The RFID (Radio Frequency Identification) is considered as one of the most preferable ways for the position estimation in indoor environments, since GPS does not work in such situations. In RFID system, an RFID reader enables to estimate the position of RFID tags easily and inexpensively. In applications with the position estimation of RFID tags, indoor robot navigations are very important for human society. The problem is how to obtain the position estimations of RFID tags as accurately as possible.

Recently, the radio frequency identification (RFID) system is paid attention as an identification source that can realize a ubiquitous environment. One of the important technologies that apply the RFID system is the indoor position estimation of RFID tags. For example, it can be applied to an indoor navigation system for handicapped person and recognition of ambient environment by a mobile robot, etc. In this paper, we propose a new positional estimation method to estimate the RFID tag position by using the tune of the antenna directivity of the RFID reader (D-CRR). This method controls the directivity of the antenna by dynamically changing the distance between the antenna elements of the RFID reader. We show the effectiveness of the proposed method by computer simulations.

RFID (Radio Frequency Identification) systems have become meaningful as a new identification source that is applicable in ubiquitous environments. Each RFID tag has a unique ID, and is attached to an object. A user reads the unique ID of an RFID tag with RFID readers and obtains the information of the object. One of the most important technologies that use the RFID system is the position estimation of RFID tags. The position estimation means to estimates the location of the object with the RFID tag. It is very useful to acquire the location information of RFID tag. If a user understands the position of the RFID tag, a new navigation system for persons in complex buildings. In this paper, we propose a new method for accurate indoor position estimation of passive RFID systems named as the Sliding-Typed CRR method. In this method, the position of an RFID tag is estimated by using S-CRR (Swift Communication Range Recognition) method. The proposed method is capable of accurate position estimation in any directions of RFID tags.

The RFID (Radio Frequency IDentification) system is paid attention to as a new identification source that achieves a ubiquitous environment. Each RFID tag has the unique ID, and is attached to some object. A user reads the unique ID of a RFID tag with RFID readers and obtains the information on the object. One of the most important technologies that use the RFID system is the position estimation of RFID tags. The position estimation means to estimates the location of the object with the RFID tag. It can be very useful to acquire the location information of RFID tag. If a user can understand the position of the RFID tag, the position estimation can be applied to a navigation system for walkers. In this paper, we propose a new method named as Swift Communication Range Recognition (S-CRR) method as an extended improvement of the previous CRR method on the estimation delay. In this method, the position of RFID tag is estimated by selecting the communication area model which corresponds to those boundary angles. We carry out the performance evaluation by the experiments of RFID system and show the effectiveness of S-CRR for position estimation.

RFID (Radio Frequency IDentification) systems have become meaningful as a new identification source that is applicable in ubiquitous environments. Each RFID tag has a unique ID, and is attached to some object. A user reads the unique ID of a RFID tag with RFID readers and obtains the information on the object.

This paper proposes a prioritized resolvable-contention-ring scheme for high-speed optical communication networks and investigates its performance. The priority mechanism is based on the time-token control scheme. This mechanism attempts to guarantee the frame delay of time-critical traffic by controlling the frame transmission of noncritical traffic. The noncritical frame can be transmitted only if token rotation time is faster than target rotation time. This paper examines the priority mechanism in the case of two priority levels and also in the case of four priority levels. System performance is studied using a computer simulation method with a time-continuous simulator. The validity of the priority mechanism is demonstrated in a comparison with a fiber distributed data interface (FDDI) and the nonprioritized resolvable-contention ring. Efficient operation of the priority mechanism is investigated by considering the buffer overflow rate of each priority class. The proposed scheme performs effectively. Moreover, the performance of FDDI is comparatively degraded because of long token waiting time and large token capture time.

This paper proposes two new access protocols, wherein the power control during transmission (PCX) scheme attempts improvement of the throughput by capture effect; this scheme is applied to s-ALOHA. Either method solves the problem of contradiction between the packet transmission time difference required in PCT scheme and the synchronized transmission as the basic requirement in PCT scheme and the synchronized transmission as the basic requirement in s-ALOHA. The first protocol is the s-ALOHA with capture interval (s-ALOHA/CI), which is concerned with the fixed-length packet format. A capture interval is provided in the first part of the slot, wherein the transmission time is selected at random to provide the transmission time difference. The second protocol is s-ALOHA with tail synchronization (s-ALOHA/TS), which is concerned with the variable-length packet format. Utilizing the variable-length property, the tail of the packet is synchronized to the tail of the slot and the packet is transmitted. Then the packet length difference produces the transmission time difference. It is verified through evaluation by analysis and simulation that the throughput performance of traditional s-ALOHA is greatly improved in either protocol by the capture effect. Especially, in contrast to the deterioration of the effective throughput of the traditional s-ALOHA due to the slot loss, it is verified that the performance of s-ALOHA/TS is better than that of the fixed-length packet scheme. These high-performance protocols will serve as a powerful means of realizing the effective operation of VSAT network, etc., with the synchronization function.

The RFID (Radio Frequency IDentification) tag is expected to be used as a tool of localization. With the localization of RFID tags, a mobile robot with an installed RFID reader can recognize the surrounding environment. In addition, it can be applied to a navigation system for walkers. In this paper, we propose a new scheme named Communication Range Recognition (CRR) in order to localize RFID tags effectively. In this scheme, the RFID reader finds the edges of the communication range when its position is moved appropriately by the robot. We evaluate the performance of the estimated position error through numerous experiments. We show that our proposed scheme can reduce the moving distance of the RFID reader without degrading the accuracy of localization in comparison with the conventional schemes.

This paper focuses on the localization technology of passive RFID (Radio Frequency IDentification) tags. By this technology, we will be able to detect some target, to get information on it, and to find the position and the distance of it. This paper proposes a novel scheme named Communication Range Recognition (CRR) in order to localize RFID tags effectively. This scheme finds the edges of the communication range of the RFID reader antenna when its position is moving by the robot appropriately. We evaluate the performance of the estimated position error through numerous experiments. We show that our proposed scheme can reduce the moving distance of the RFID reader without degrading the accuracy of localization in comparison with the conventional schemes.

Optical Burst Switching (OBS) has been proposed to realize the next generation Internet on the Wavelength Division Multiplexing (WDM) network technology. Optical Burst Switching is an ultra high speed switching technology for optical fiber networks but has the data burst contention problem. In this paper, we introduce Virtual Path (VP) concept addressing burst contention resolutions in OBS networks. We propose two novel flow control schemes, named Static Inter Arrival Time Flow Control (S-IAT) and Dynamic Inter Arrival Time Flow Control (D-IAT). S-IAT keeps the data burst contention rat e in an acceptable level on OBS networks. Based on S-IAT, D-IAT achieves almost the same data burst contention rate and higher throughput than S-IAT by using the data burst loss rate threshold. We will show the availability of proposed schemes by computer simulations.

Recently, the RFID tag system is paid attention to as an identification source. Each RFID tag is attached to some object. With the unique ID of RFID tag, a user identifies the object provided with the RFID tag, and derives appropriate information about the object. One of the important applications of 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 plural communication ranges. We show the effectiveness of the proposed method by computer simulations.

The advent of VSAT (very small aperture terminal) has made it possible to consider a new utilization of satellite communication. This paper proposes a new access protocol v-ALOHA, which is matched to the characteristics of the packet switching network based on VSAT. p-ALOHA is used as a means to cope with the requirement for simplification. To complement its disadvantage of low through-put, a new control scheme is combined based on the new utilization. The performance is improved by the capture effect. The basic idea of the control scheme is to vary the power with time while transmitting packets. The difference in the transmission-start time is converted into the power difference and produces the capture effect, thereby improving the performance. Thus, an access protocol is realized which improves the low throughput of p-ALOHA while preserving its simplicity. This paper describes the basic idea of this v-ALOHA and the protocol structure, indicating qualitatively its features. Then the throughput performance is formulated through a quantitative analysis. It is shown from the numerical results for the fixed-length packet that the performance of the proposed scheme is better than other capture schemes, approaching sufficiently the performance of s-ALOHA. For the case of the variable-length packet, there is no slot loss as in s-ALOHA, and the proposed scheme is shown, using an example, to be better sometimes than s-ALOHA.

The RFID (radio frequency identification) tag 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, it 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.

Recently, we need high bit rate transmissions of the wireless LAN to access the internet at offices and houses. Multi-Poll access scheme has been proposed as an efficient access control scheme for these necessities. The scheme is a central control scheme using Polling system. In order to establish a high speed multimedia transmission, we need to integrate the required quality of services effectively. In this paper, we propose QoS (Quality of Service) guaranteed Multi-Poll access scheme for multimedia services in wireless LAN. We evaluate the transmission performances of the proposed scheme for effectiveness by computer simulations. We have clarified that the proposed scheme has the outstanding performances on the throughput, delay time, and frame drop rate comparing to the conventional scheme.

Using the rate control to restrict the peak cell rate of traffic is addressed. The asynchronous transfer mode (ATM) environment is considered as a discrete-time environment in which one slot is equal to one cell transmission time. A rate control that can restrict the number of cells during any fixed-length time interval in a discrete-time environment is studied. The scheme is realized by means of simple counter accumulation per slot, and it is easy to synchronize with slots. The simplicity of this scheme may make possible the flexible restriction of the peak cell rate according to network conditions. The scheme is analyzed, using matrix analytic techniques, in order to investigate the smoothing effect of bursty traffic and the queue length required to satisfy a certain quality of cell loss probability. Numerical results show the effect of restricting the peak cell rate of bursty traffic and the tradeoff between the smoothing effect and the required queue length. >

Presents a new access control scheme for the wireless communication packet networks of variable packet length environment, s-ALOHA/PAIT (slotted ALOHA with power assigning and immediate transmission controls). The scheme improves channel throughput in two aspects, capture effect and reuse of vacant period of a slot. For reuse of vacant period of a slot, a packet can be transmitted immediately unless it overrides the slot boundary even though the timing is not at the beginning of the slot. It enables more than one packet to be transmitted successfully in a slot. Transmission power is varied to lead capture effect among packets transmitted at the beginning of a slot and also between a packet at the beginning of a slot and one transmitted in the middle of the same slot. The authors evaluate the performance of s-ALOHA/PAIT compared with the conventional s-ALOHA and show that s-ALOHA/PAIT obtains considerable improvement of the throughput performance. >

The performance of a homogeneous multiprocessor system with common memory contentions is evaluated in this paper. A symmetric continuous-time Markovian queueing network model is developed and analyzed. The main result is that the average number of active processors, as an important performance measure, is derived and given by a very simple recursive formula. Using the result, several properties of the multiprocessor system are proved analytically. It is found that a profound performance measure defined as processing power saturation ratio is significant in the evaluation of multiprocessor systems. Some numerical examples are also available to verify the obtained results.