論文

After investigating the potential market for satellite communications in around 2010 that will have advantages over future terrestrial communication networks, we concluded that there will be a large demand for broadband communications services for passengers in vehicles such as long-haul trains, seagoing vessels, and airplanes. In this article, we describe a next-generation broadband scalable mobile satellite communication system for Japan that can offer economical broadband Internet service for passengers in such vehicles. We describe possible services, estimate the potential market, and discuss the requirements for such services to flourish. Finally, we discuss enabling technologies required for the system.

When a multitude of RFID tags are in the interrogating field, an anti-collision technology must be used. In literatures, the reading performance was mainly investigated on the error-free communication links between reader and tags. In the practical situations, particularly where a number of readers and other wireless devices share the same frequency band, the performance on the erroneous links would be significant interest. In this paper, we evaluated Gen2 Air Protocol paying attention to the anti-collision performance in random error communication link. As a result of simulation, two findings were obtained. Firstly, there is an appropriate number of slots depending on the number of tags. This number hardly changes even if a random error is incurred on the link. Secondly, the singulation speed might be significantly degraded particularly in erroneous links, if the optimal number of slots is not chosen. The findings can be interpreted such that the necessary link quality can be derived if the number of tags and permissible time are known a priori to the implementation. For instance, if 64 tags are required to be read in one second, it is necessary to ensure the link quality to be better than BER=10-4 in random error environment. © 2005 IEEE.

Readability of passive RFID fundamentally depends on the tag empowering. The minimum required power, usually referred to as sensitivity, depends on the chip and antenna manufacturing. The sensitivity affects the readability but it is not the sole determinant of readability. The readability of RFID comprises a number of factors, particularly in the UHF band. This paper proposes a classification of tag readability degradation factors and measurement methods to quantify the factors. It is shown that tag performance change at the attachment may affect the readability. A tag probe, a power measurement antenna at the position of tag attachment, can monitor essential data to comprehend the situation and establish a countermeasure to improve the tag readability. The operating environment, involving reader antenna positions and standing waves result from the multipath fading, is another important factor for the readability. The characteristics of the environment could be also grasped by using the tag probe. © 2005 IEEE.

We describe a layer 3 diversity reception scheme that enhances the transmission characteristics of Ku-band mobile satellite communication systems. This scheme can realize high-speed communication for vehicles that experience shadowing caused by terrestrial obstacles such as tunnels, buildings and bridges, especially for trains that frequently experience shadowing from the trolley wire structures. Layer 3 diversity was chosen for long distance diversity to prevent signal shadowing caused by terrestrial obstacles while minimizing the alterations of existing receivers. The technology enables high-speed communication under shadowing conditions in a running train environment. Copyright © 2006 The Institute of Electronics, Information and Communication Engineers.

Incorporation of heterogeneous wireless sensor and actuator networks (WS&AN) is an essential challenge of web based Internet of Things (IoT) architectures. We propose to use UPnP and end-to-end HTTP communication using CoAP to bridge WS&AN and IoT system. UPnP enables automatic discovery of sensor devices which directly connect to a WS&AN via a gateway. Instead of translating WS&AN and UPnP protocols at the gateway, we propose to use CoAP in WS&AN. This provides flexible communications between sensor devices and applications. Drawback of this end-to-end Web based IoT information system is vulnerability to excessive traffics from sensor devices or from the applications because there is no authority to monitor and control traffics in the architecture. We examined the performance of our implementations to find that the transmit performance of a single sensor device could be limited by the serial communications of embedded transceiver. Excessive data requests from applications might also result in the packet loss and wasteful WS&AN congestion. If the traffic is confined within the performance limits, the implemented UPnP and ZigBee bridging using CoAP shows satisfactory performance. We can subscribe up to 16 sensor devices data with 500 msec using simple HTTP POST requests. © 2011 ACM.

RFID is an essential technology to uniquely identify physical objects. In many practical business processes using RFID, we check not only individual objects but also check if there is no missing objects and no extra objects in a group of objects. While individual objects identifications are done by using RFID, group verifications are usually done by looking up a shipping list or corresponding EDI data which require a network connection. In this paper, we propose "group coding of RF tags" by which we can verify the integrity of a group of objects just by writing additional data in RF tags' memory. The additional data is computed from unique IDs of objects that belong to the group. We propose fundamental and general group codings. With the fundamental group coding, we can check if the integrity of a group of objects is preserved or not. It is a parity check of hashes of unique IDs in a group. We also propose general group coding by extending the fundamental group coding. With the general group coding, we can estimate the number of missing objects if the integrity of a group is not verified. The strength of the missing number estimation can be controlled by the size of data written to RF tags. It can be considered as a Low Density Parity Check (LDPC) in physical objects. The theory of group coding is confirmed by a numerical simulation and an experiment. It is shown by the simulation and experiment that we can detect 10 missing RF tags out of 20 RF tags with 99.5% reliability by writing 96-bit data into each RF tags besides its 96-bit unique ID. © 2011 IEEE.

The Internet of Things is a concept of connecting small real space physical objects to the Internet using sensor network, RFID, and other forms of wireless network technologies. In this paper, we present an EPC (Electronic Product Code) based Internet of Things (IoT) architecture. The key concept of the architecture is EPC network over heterogeneous access network. We particularly focused on a ZigBee network as it can collect the latest information about 'Things'. The EPC Network provides certain static information about 'Things' such as name and manufacturer. To support end-to-end communication between sensor nodes and applications, Constrained Application Protocol (CoAP) instead of Hyper Text Transfer Protocol (HTTP) over ZigBee is developed. A gateway on a local area network converts HTTP and CoAP. A pseudo Universal Plug and Play (UPnP) protocol supports JOIN/LEAVE management of sensor nodes. We also prove a prototype home appliances management system that adopt our architecture over a ZigBee network. Our prototype provides energy-saving application using home appliances information collected through the system. © 2011 IEEE.

We have developed a system using a combination of a multi-hop sensor network and 3G networks to support patients daily medication in home care. Each medication of a patient is represented by a sequence of close-open-close events of an off-the-shelf pill box, which are detected by a small Hall sensor. The system enables home visiting nurses to remotely monitor their patients' medication and to give feedback on the medication status to patients. This bidirectional communication between medical staff and patients is essential to motivate patients' medication and to make their experience of being taken care for at homes more comfortable. A semi-automatic message generation system helps medical staff to send feedback without spending excessive time and effort. We have been examining this system for more than three months with three subjects and found that a simple open/close sensing of an off-the-shelf pill box can provide a valuable medication history. It has also shown that the feedback system improves the rate of failure medication from 5.3% to 0.0% in the best case. © 2011 IEEE.

In any sensor information system, unique identification (ID) of each sensor is indispensable. Usual practices to secure uniqueness of sensor ID is to use MAC or network address or to use a proprietary ID in application layer. In pervasive computing era, it is desirable to uniquely identify a sensor with a URN regardless of types of network to which the sensor is connected. This paper proposes to embed a dual interface RF tag, which records a globally unique ID, EPC (Electronic Product Code), used in business transactions, to sensor microcontroller(MCU). The dual interface RF tag allows us to access its tag data either via RF interface and a baseband interface. This enables a sensor MCU to use EPC to uniquely identify the sensor for its whole product lifecycle. Since EPC have been only accessed through the RF interface, we developed a modified UPnP to automatically discover EPC enabled sensors through the baseband interface for various access networks. Taking advantage of the existing network RFID architecture, we can search services related to an EPC in a form of URL and also can publish and subscribe sensor data service with a standardized web service interface. This paper reports a hardware implementation of dual interface RF tag with a ZigBee transceiver. Timing requirement of RFID protocol to access RF tag's memory can be met by a software control of off-the-shelf MCU GPIO. A 96 bits EPC stored in an dual interface RF tag can be retrieved in 12.3 msec. For the automatic device discovery of an EPC enabled sensor attached to a ZigBee network, a modified UPnP is also developed. The proposal is implemented in a working prototype with 49 sensors which geographically dispersed in 3 locations which can continuously collect 181 sensor data for various applications. We also evaluated the minimum time interval to publish sensor data to find 300 msec is the shortest interval in our implementation. This interval is dominated by the communications capacity between sensor MCU and on-board transceiver chip. © 2011 IEEE.

Consider a situation where one desires to retrieve sensor data from an arbitrary environment via a moving interrogator. Maintenance of street lights and electric apparatus in conduits for example. The fundamental problems with this system have been 1)the trade-off relation between power consumption by sensor and the data retrieval rate for the interrogator, and 2)the data retrieval agility for the moving interrogator. A higher duty ratio incurs more power consumption in sensors whereas a lower duty ratio leads to a less reliable retrieval rate. Even though there have been such efforts as"adaptive sleep period control" which was derived form the packet arrival rate,they didn't systemically solve the problem, particularly for moving-interrogator environment. This paper presents a solution of separating the timing of sensor-sampling and the timing of sensor-data retrieval. The asynchronous data retrieval mechanism is facilitated by a dual interfaced UHF passive RF tag known as a " record tag "which the authors have been developing. This paper examines the power consumption composition of a prototype recorder tag. The power consumption efficiency of the proposed data-retrieval method is discussed in comparison with that of the existing method in term of " Sensor Sampling Interval vs.Battery Life Expectancy"The author also evaluated the viability of retrieving sensor data through a moving-interrogator. We specifically inspected the relationship of " Interrogator's moving Speed vs Successful Data Retrieval Rate "The tests showed that with a commercial 1.2V rechargeable battery, the recorder tag lasts for 21 days forluminance and temperature sensing using a 30 minute samplinginterval, extending the traditional battery lifespan ten times longer, yet still preserving 100% time availability for sensor data retrieval. The power consumption is expected to be eight times as efficient when using optimized circuitry. Experiments in an emulated fading environment reveal that the data retrieval rate is observed to be the highest when the maximum relative speed between the moving-interrogator and the recorder tag is less than 3km/h, with an optimized distance of separation being 10cm for a 27dBm EIRP interrogator. The moving speed, 3km/h, can be improved by optimizing the anti-collision procedure and by enhancing the sensitivity of the recorder tag. © 2010 IEEE.

In a long-range RFID system, the communication range is far longer than that in a conventional short-range RFID system. However, the long-range RFID system tends to suffer interfering problem between systems. In this report, we evaluate the interference avoidance method of assigning the frequency channels and time slots to reader with using the information of the reader position. From the computer simulation, we show that the number of required time slots for avoiding the interference can be reduced and the frequency utilization efficiency can be increased when the dependence between the interference geometrical distance between readers and the frequency distance between channels is taken into account. © 2010 IEEE.

UHF band passive RFID is an essential identification technology in pervasive computing world. One of the industrial demands to UHF band passive RFID is fast reading of many RF tags. This is particularly relevant for item-level-tagging of CDs, DVDs, books and consumer electronics. Many high-speed MAC protocols have been proposed thus far. Quantitative evaluation of reading speed, however, is not easy because we need to lay out many RF tags and measure the reading durations usually through interrogator APIs, which differ from interrogator to interrogator. In this paper, the authors propose two efficient multiple RF tag emulation algorithms which leverage the probabilistic nature of MAC protocol. We have implemented the algorithms onto a programmable battery assisted passive tag (BAP), equipped with an 8bit micro processor and evaluated the reading speed of commercial interrogators. It was revealed that the BAP can efficiently emulate the behavior of more than 1000 Gen2 RF tags for the reading speed evaluation with a trivial penalty on accuracy. ©2010 IEEE.

UHF band passive RFID systems are being steadily adopted by industries because of their capability of long range automatic identification with passive tags. For an application which demands a large number of readers located in a limited geographical area, referred to as dense reader mode, interference rejection among readers is important. The coding method, baseband or subcarrier coding, in the tag-to-reader communication link results in a significant influence on the interference rejection performance. This paper examines the frequency sharing of baseband and subcarrier coding UHF RFID systems from the perspective of their transmission delay using a media access control (MAC) simulator. The validity of the numerical simulation was verified by an experiment. It is revealed that, in a mixed operation of baseband and subcarrier systems, assigning as many channels as possible to baseband system unless they do not exploit the subcarrier channels is the general principle for efficient frequency sharing. This frequency sharing principle is effective both to baseband and subcarrier coding systems. Otherwise, mixed operation fundamentally increases the transmission delay in subcarrier coding systems. Copyright © 2009 The Institute of Electronics, Information and Communication Engineers.

Recently, system designers, especially in the field of product life-cycle management system start considering use of user memory bank of UHF RFID tags. By storing most useful life-cycle data onto a tag, user can access to the data even without access to back-end databases. One of the major issues to make use of the user memory bank is detection of memory tampering. Although technology vendors start introducing new functionalities such as fine grained locking along with high capacity user memory, these tags with new functionalities require new non-standardized air protocol to operate - require modified version of reader/writers. Also, these tags are usually more expensive. In this paper, we introduce a novel approach to this problem: tag side write journaling mechanism and "Tag Memory Cloaking," which protect the journal by using. Tag Private Memory region, which is only readable and not writable from external devices such as a reader/writer, but writable by tag itself. Also, any write to the user memory automatically add journal entry - offset and length of the write - into the Tag Private Memory region. Later, a user can check existence of overlapped writes to user memory by checking the journal records. Since we have not modified any of air protocol, standard compliant read/writer can fully capable of all of our proposed operations: write to the tag, read, then detect unusual modification to user memory area. We have implemented the functionality to Programmable Battery Assisted Passive tag (BAP), then validated the method with several standard compliant reader/writers. © 2008 IEEE.