論文

Physical objects often form a group such as objects in a shipping container. RFID enables us to identify each object and even the container itself. However, current RFID does not provide information on IDs missing from a group. This paper proposes a method to determine the unique IDs of objects missing from a group without any external database or verifier. The proposed method logically splits a group into mutually overlapped sub-groups and writes group-related information, which is generated from the unique IDs of objects in the subgroup, to RF tags' memory. When we check the integrity of a group of objects, unique IDs and group-related information of RF tags are extracted from RF tags' memory. With an iterative decoding over group-related information with the unique IDs of identified objects, missing IDs are determined. A numerical simulation reveals that the proposed method can identify 96-bit unique IDs of up to 64 objects missing from a group composed of 100 objects by writing 840-bit group-related information to each RF tag. We also examined the performance with an experiment and confirmed that we can successfully determine 16-bit IDs of up to 12 missing RF tags from a group of 20 RF tags by writing 280-bit group-related information to each RF tag. The experiment results agree well with the numerical simulation. © 2012 IEEE.

Occupancy determination of a large room, such as university campus room, using pyroelectric infrared (PIR) sensors is difficult because PIR sensors are inherently insensitive to humans that are motionless and it is difficult to achieve 100% coverage even with multiple sensors. To overcome these problems, the authors propose using particle filtering of networked multiple PIR sensor data to improve the accuracy of the occupancy state determination. The particle filtering can eliminate incorrect occupancy state transition without incurring large delays. Our method is robust to the incompleteness of the coverage and accuracy. The authors performed an experiment in a campus room (15.3m×6.4m) with 4 PIR sensors to prove the validity of the proposal. The experiment shows that the proposal can improve the occupancy determination accuracy from 29.6% to 98.3%. The system has been continuously used in the university power saving project. © 2012 IEEE.

This study proposes a collateral registration method of asset based lending (ABL) and evaluates parameters of supply chain management (SCM) operation that affect performance of ABL. Radio frequency identification has been deployed recently and there increases the application areas using its track and trace capability. ABL is one of them, in which company borrows money from financial service company (FSC) by using movable asset, such as inventory, as collateral. We proposed a registration method that is compatible to the current RFID standard, analyzed the SCM parameters that affect the loan condition of ABL, and summarized how companies design the SCM operation to take advantage of the financing scheme. © 2012 IEEE.

Radio frequency identification (RFID) is an automatic identification technology which identifies physical objects individually according to their unique identifiers (ID) recorded in each RFID tag. Many business processes require the integrity verification of a group of objects in addition to individual object identification. This paper proposes "group coding" of RFID tags with which we can verify the integrity of groups of objects by writing parity check data to the memory of RFID tags. It was revealed by simulations and experiments that we could determine the number of missing RFID tags up to 10 with accuracy over 99% when we write 96 bits of the checksum data to 20 RFID tags. The whole duration of group decoding measured in the experiment was approximately 2 to 3 s. The time to compute group encoding and decoding was in the order of several milliseconds and thus negligible. The RFID inventory accounts for the majority of the duration. © 2004-2012 IEEE.

Flexible multibody dynamics is applied to the deployment analysis of a large space antenna composed of a reflective mesh, a cable network and a deployable truss structure. It is clarified that the tension of some of the cables increase when the reflector is stowed. The largest deployment force is observed slightly before the completion of the deployment. A proper allocation of both translational and rotational springs can provide an efficient deployment force. A deployment experiment on a 4.8 m aperture reflector model verifies the computational results. It is concluded that a flexible multibody dynamics simulation is an indispensable design tool for reducing the weight and ensuring the secure deployment of low-cost mesh reflectors.

The authors have been developing a large deployable mesh reflector for advanced satellite communication. This large reflector consists of a mesh membrane surface and a deployable truss structure. In this paper, analysis methods for a large deployable mesh reflector structure are introduced, and the theoretical basis for the analysis is explained. By using those analysis methods, we manufactured prototype reflector modules and carried out an experiment on them. The validity of the analysis methods were verified from the results of the analyses and experiments. The design procedure of mesh reflector surface and the effect of the mesh surface tension on the truss deployment are discussed.

Single-hop connection methods, which establish direct mobile to mobile communication links in the existing domestic mobile satellite communications system, are investigated. The difficulty for the single-hop connection stems from the PDC frame format, in which traffic and control channels reside in one frame. Two single-hop connection methods, based on a non-regenerative transponder satellite and a regenerative transponder satellite, are derived and evaluated in accordance with the required functionality on mobile terminal, base station and satellite. In each of the two methods, the satellite transponder has to involve such circuit as narrow-band filter bank, channel switch and beam switch. A regenerative transponder satellite has to have MODEM and frame decompose/compose circuits, additionally. Those circuits can be build by applying digital signal processing technology with relatively small circuit under a given satellite life time and space environment.

We have proposed the mobile multimedia satellite communication system designed to realize high-speed multimedia communications. This system uses a mobile network for the return link and the newly developed satellite-tracking antenna that receives high-speed satellite signals for the forward link. This paper describes the system configuration featuring the satellite-tracking antenna performance and network performances measured by network throughput. The satellite-tracking antenna achieves 0.42 degree rms and 0.13 degree rms accuracy in the azimuth and the elevation, respectively. These accuracies meet the pointing loss requirements, 1 dB, in the link analysis. Even in mobile environments, 1 Mbit/s of throughput, which is limited by the system round trip time, can be achieved for file downloading when TCP is used as the transport protocol. This throughput can be improved when XTP is applied as the transport protocol.

We have proposed a mobile multimedia satellite communication system designed to realize high-speed multimedia communications. This system uses a mobile network for the return link and a newly developed tracking antenna that receives high-speed satellite signals for the forward link. This paper describes the system configuration, the tracking antenna performance and the IP network's performance in mobile environments. The tracking antenna was accurate to within 0.80 degree rms and 0.25 degree rms in azimuth and elevation, respectively. These accuracies meet the pointing loss requirement, 1 dB, in the link analysis. The network performance of the system was evaluated both in stationary and mobile environments by measuring the round trip time and the throughput. These characteristics were measured for several return link implementations, e.g., PDC (Japanese Cellular Standard), PDC-Packet (Packet communication service of PDC) and Satellite phone. Even in mobile environments, 1 Mbit/s of throughput, which is limited by the system round trip time, can be achieved for file downloading with TCP as transport protocol. This throughput can be increased to almost the network limit when XTP is applied as the transport protocol. © 2002 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

This paper presents a new automatic-frequency control (AFC) configuration capable of removing a large amount of frequency offset (up to about +/- 0.625 fs, where fs means symbol rate of signals). The new AFC consists of the AFC that removes frequency offsets between +/- 0.125 fs and another AFC that detects the frequency offset range coarsely between +/- 0.625 fs. First, the principle of the new AFC configuration is described. Then, the performance of the new AFC is confirmed via computer simulation. It is shown that the proposed AFC configuration can accommodate wide range frequency offsets as well as reduce the acquisition time. © 2003 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

In order to realize lightweight onboard satellite antennas, we proposed a technique that uses linear interpolation to reduce the number of control circuits. Compared to the conventional approach, the reduction is about 70%. To apply the technique to practical multi-beam systems with frequency reuse, it is necessary to meet the requirement in term of beam isolation. This paper presents a method for determining the excitation weights so as to meet the requirement of multi-beam systems with frequency reuse. We confirm the validity of the method by calculating the antenna patterns generated by the excitation weights output.

Satellite communication systems have entered the mobile multimedia communication era. To support small earth terminals, the satellites must have high levels of effective isotropic radiated power. Onboard high-power amplifier not only need to generate high RF output power, but also to generate as little heat as possible. To address this issue, we present a new technique that reduces the amount of heat generated in high power amplifiers on a satellite. The technique makes use of heat suppression signals so as to maintain the amplifier's power efficiency. The potential impact on satellite systems is presented. To minimize the interference of the heat suppression signals on the carrier, some techniques are proposed using a multi-port amplifier and an antenna array and a reflector. © 2003 by the American Institute of Aeronautics and Astronautics, Inc.

This paper presents the results of train experiments and their analysis of Ku band mobile multimedia satellite communication system. First, the requirements for the satellite-tracking antenna are described. And then, the satellite signal availability as well as the network performance, which were measured on trains, are described. Based on these data, it is confirmed that the satellite visibility from a train, which varies in accordance with the train's route, can be related to network throughput and the network throughput can be conceived as a high-speed Internet access. It is verified that major cause of network throughput degradation was identified by our laboratory tests. © 2003 by the American Institute of Aeronautics and Astronautics.

A layer 3 diversity reception scheme that enhances the transmission characteristics of Ku band mobile satellite communication systems is presented. The initial thrust for developing this scheme is to realize high-speed communication for trains that experience shadowing caused by terrestrial obstacles such as tunnels, buildings, bridges and structures that support trolley wires. Layer 3 diversity was chosen for long distance diversity to prevent signal shadowing caused by terrestrial obstacles and to yield packets in the same order as in the original packet stream while minimizing the alterations of existing receivers. The technology enables high-speed communication under simulated shadowing conditions in a running train environment while assuring correct packet order. Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

A formula of multibody finite element analysis based on the corotational formulated finite element method and the direct coordinate partitioning for deployable truss structures is proposed. A beam element used in linear finite element analyses is a basic element in the formula. A corotational frame is defined by node coordinate systems attached to a beam element. A tangent stiffness matrix contains a virtual rotation displacement of the corotational frame. By the appropriate transformation of this virtual displacement, a simple geometric stiffness for the formula is obtained. The formula makes it possible to analyze the deploying motions of large deformed deployable truss structures, to be applicable to general finite elements, and to increase convergence speed of the Newton method in a solution algorithm. This improvement is achieved by neglecting virtual work done by rigid body motion in the process of employing the geometric stiffness to the conventional formula. A validity of this formula is confirmed through results of a numerical deployment analysis of a deployable beam structure.

This paper presents a new automatic-frequency control (AFC) configuration capable of removing wide range frequency offsets (up to about ±0.625 fs, where is is signal symbol rate). The new configuration consists of an AFC that removes frequency offsets between ±0.125 fs and another AFC that detects the frequency offset range coarsely between ±0.625 fs. This paper describes the principle of the new AFC configuration. The proposed AFC configuration employs four correlators to enhance the acquisition range. It also adopts the reverse modulation scheme to decrease the acquisition time. The performance of the new AFC configuration is confirmed via computer simulations. It is shown that the proposed configuration can accommodate wide range frequency offsets as well as reduce the. acquisition time.

The phased array fed reflector antennas with interpolation network for next generation mobile satellite communication systems are discussed. A small satellite, such as 2kW-payload power, was used to reduce system cost. The improvement in onboard antenna performance is achieved by increasing reflector diameter. A modification of the directional constrained minimum power (DCMP) method is proposed to handle interpolation networks. The validity of the method is confirmed by calculating antenna patterns of a designed phased-array-fed reflector antenna.

Mobile satellite communication systems are attracting much attention as an effective way to provide broadband communications in planes, ships, and long-haul trains in which economical services are not effectively provided by terrestrial systems. Such a system usually requires a wide frequency bandwidth and a satellite with high electrical output power, but these resources are severely restricted. A multi-beam system with frequency reuse is able to spread the usable bandwidth virtually. Applying an adaptive modulation method to the system achieves efficient use of resources. In this system, optimally assigning resources to beams is indispensable in enhancing the system capacity. However, this optimization method becomes complex since it is necessary to consider the influence of inter-beam interference which may depend on the variation in the communication traffic distribution. We propose a new adaptive resource assignment method in order to overcome this complexity and to enhance the system capacity. In the proposed method, a bandwidth vector and an approximate curve of the spectrum efficiency are introduced. Based on case studies assuming 19 beams, we show that the proposed method achieves 4.2 times higher system capacity than that of a system in which resources of each beam are fixed. Copyright © 2004 by NTT Corporation.