XML query processing is one of the most active areas of database research. Although the main focus of past research has been the processing of structural XML queries, there are growing demands for a full-text search for XML documents. In this paper, we propose XICS (XML Indices for Content and Structural search), which aims at high-speed processing of both full-text and structural queries in XML documents. An important design principle of our indices is the use of a B+-tree. To represent the structural information of XML trees, each node in the XML tree is labeled with an identifier. The identifier contains an integer number representing the path information from the root node. XICS consist of two types of indices, the COB-tree (COntent B+-tree) and the STB-tree (STructure B+-tree). The search keys of the COB-tree are a pair of text fragments in the XML document and the identifiers of the leaf nodes that contain the text, whereas the search keys of the STB-tree are the node identifiers. By using a node identifier in the search keys, we can retrieve only the entries that match the path information in the query. The STB-tree can filter nodes using structural conditions in queries, while the COB-tree can filter nodes using text conditions. We have implemented a COB-tree and an STB-tree using GiST and examined index size and query processing time. Our experimental results show the efficiency of XICS in query processing.

Our group is exploring interactive multi- and hypermedia, especially applied to virtual and mixed reality multimodal groupware systems. We are researching user interfaces to control source→sink transmissions in synchronous groupware (like teleconferences, chatspaces, virtual concerts, etc.). We have developed two interfaces for privacy visualization of narrowcasting (selection) functions in collaborative virtual environments (CVES): for a workstation WIMP (windows/icon/menu/pointer) GUI (graphical user interface), and for networked mobile devices, 2.5- and 3rd-generation mobile phones. The interfaces are integrated with other CVE clients, interoperating with a heterogeneous multimodal groupware suite, including stereographic panoramic browsers and spatial audio backends & speaker arrays. The narrowcasting operations comprise an idiom for selective attention, presence, and privacy-- an infrastructure for rich conferencing capability.

Elliptic curves offer interesting possibilities for alternative cryptosystems, especially in constrained environments like smartcards. However, cryptographic routines running on such lightweight devices can be attacked with the help of "side channel information"; power consumption, for instance. Elliptic curve cryptosystems are not an exception: if no precaution is taken, power traces can help attackers to reveal secret information stored in tamper-resistant devices. Okeya-Takagi scheme (OT scheme) is an efficient countermeasure against such attacks on elliptic curve cryptosystems, which has the unique feature to allow any size for the pre-computed table: depending on how much memory is available, users can flexibly change the table size to fit their needs. Since the nature of OT scheme is different from other side-channel attack countermeasures, it is necessary to deeply investigate its security. In this paper, we present a comprehensive security analysis of OT scheme, and show that based on information leaked by power consumption traces, attackers can slightly enhance standard attacks. Then, we explain how to prevent such information leakage with simple and efficient modifications.

This paper examines polarimetric scattering characteristics caused by a dihedral corner reflector of finite size. The dihedral corner reflector is a basic model of double-bounce structure in urban area. The detailed scattering information serves the interpretation of Polarimetric Synthetic Aperture Radar (POLSAR) data analysis. The Finite-Difference Time-Domain (FDTD) method is utilized for the scattering calculation because of its simplicity and flexibility in the target shape modeling. This paper points out that there exists a stable double-bounce squint angle region both for perfect electric conductor (PEC) and dielectric corner reflectors. Beyond this stable squint angular region, the scattering characteristics become completely different from the assumed response. A criterion on the double-bounce scattering is proposed based on the physical optics (PO) approximation. The detailed analyses on the polarimetric index (co-polarization ratio) with respect to squint angle and an experimental result measured in an anechoic chamber are shown.

An effective access control scheme in CDMA networks is proposed to provide multimedia services. The proposed scheme controls the access of multimedia traffic using the delay of data traffic and the transmission rate control of video traffic. Numerical results show that throughput and delay are improved by allowing delay of data traffic under low and medium traffic conditions, and by decreasing the transmission rate of video traffic under heavy traffic conditions.

This paper focuses on algorithms for an efficient scalar multiplication. It proposes two algorithms for computing points of the form 2kP in affine coordinates. One works for k=2, and the other works for an arbitrary natural number k. The efficiency of these algorithms is based on a trade-off between a field inversion and several field multiplications. Montgomery trick is used to implement this trade-off. Since a field inversion is usually more expensive than 10 field multiplications, the proposed algorithms are efficient in comparison with existing ones.

We propose a new security class, called plaintext simulatability, defined over the public-key encryption schemes. The notion of plaintext simulatability (denoted PS) is similar to the notion of plaintext awareness (denoted PA) defined in [3], but it is "properly" a weaker security class for public-key encryption. It is known that PA implies the class of CCA2-secure encryption (denoted IND-CCA2) but not vice versa. In most cases, PA is "unnecessarily" strong--In such cases, PA is only used to study that the public-key encryption scheme involved meets IND-CCA2, because it looks much easier to treat the membership of PA than to do "directly" the membership of IND-CCA2. We show that PS also implies IND-CCA2, while preserving such a technical advantage as well as PA. We present two novel CCA2-secure public-key encryption schemes, which should have been provided with more complicated security analyses. One is a random-oracle version of Dolev-Dwork-Naor's encryption scheme [8],[9]. Unlike the original scheme, this construction is efficient. The other is a public-key encryption scheme based on a strong pseudo-random permutation family [16] which provides the optimal ciphertext lengths for verifying the validity of ciphertexts, i.e., (ciphertext size) = (message size) + (randomness size). According to [19], such a construction remains open. Both schemes meet PS but not PA.

In this paper, we propose an angle of arrival (AOA)-based beamforming structure with strong interference resistant capability for OFDM systems. First, we present novel interference resistant angle of arrival (AOA) estimation schemes for each multipath without training sequences or symbols as the pre-processing of the proposed structure. The generalized sidelobe canceler (GSC) structure is thus applied with the AOA information to avoid calculating the beamforming weight vector individually on a per subcarrier basis, wherein the GSC structure with the reduced-rank multistage Wiener filter (MSWF) is adopted. We also propose a signal transformation scheme to improve performance before the signals are fed into the GSC receiver. The proposed receiver offers better performance than the GSC form of the constrained Wiener filter-based receiver due to the faster convergence property of reduced rank processing and the signal transformation scheme.

It has recently been reported that the performance of hyperelliptic curve cryptosystems (HECC) is competitive to that of elliptic curve cryptosystems (ECC). Concerning the security of HECC, the theta divisors play an important role. The scalar multiplication using a random base point is vulnerable to an exceptional procedure attack, which is a kind of side-channel attacks, using theta divisors. In the case of cryptographic protocols of the scalar multiplication using fixed base point, however, the exceptional procedure attack is not applicable. First, we present novel efficient scalar multiplication using theta divisors, which is the positive application of theta divisors on HECC. Second, we develop a window-based method using theta divisors that is secure against side-channel attacks. It is not obvious how to construct a base point D such that all pre-computed points are theta divisors. We present an explicit algorithm for generating such divisors.

This paper reports on an evaluation result of current obfuscation techniques for Java byte code, such as Collberg's techniques in terms of mutational capability, real-time applicability, and program size increase. We suggest effective obfuscation techniques for random and real-time obfuscation (RR obfuscation). In the evaluation results, the combination of some obfuscation techniques was found to be useful for RR obfuscation, and some obfuscation techniques makes little or no difference after a certain threshold.

Space-frequency transmit diversity (SFTD) and space-code transmit diversity (SCTD), which are both based on space-time block codes (STBC), were applied to time-direction spreading and two-dimensional spreading orthogonal frequency-division multiplexing code-division multiplexing (OFDM-CDM) systems, and the transmission performances were compared by computer simulation. SFTD is designed for space and two adjacent subcarriers whereas SCTD is designed for space and two distinct Walsh-Hadamard (WH) codes. The simulation results show that SCTD applied to time-direction spreading OFDM-CDM was superior to SFTD because frequency selectivity distorted STBC's orthogonality between sub-carriers in SFTD. In contrast, when they were applied to two-dimensional spreading OFDM-CDM, SFTD was superior to SCTD when the number of WH codes belonging to the same mother-code group is small because the frequency diversity provided by SFTD surpassed that provided by SCTD. In addition, both SFTD and SCTD provide high tolerance to large Doppler spread. It can be therefore concluded that both SCTD and SFTD can be used in the same frame by code-multiplexing according to their suitability to physical channels. SCTD is suitable for transmitting high-rate data via time-direction spreading, whereas SFTD is suitable for transmitting control data via two-dimensional spreading.

To find the best transformation between a "model" point set and an "image" point set is the main purpose of point pattern matching. The similarity measure plays a pivotal role and is used to determine the degree of resemblance between two objects. Although some well-known Hausdorff distance measures work well for this task, they are very computationally expensive and suffer from the noise points. In this paper, we propose a novel similarity measure using the Hilbert curve named Hilbert scanning distance (HSD) to resolve the problems. This method computes the distance measure in the one-dimensional (1-D) sequence instead of in the two-dimensional (2-D) space, which greatly reduces the computational complexity. By applying a threshold elimination function, large distance values caused by noise and position errors (e.g. those that occur with feature or edge extraction) are removed. The proposed algorithm has been applied to the task of matching edge maps with noise. The experimental results show that HSD can provide sufficient information for image matching within low computational complexity. We believe this sets a new direction for the research of point pattern recognition.

The Gallant-Lambert-Vanstone method [14](GLV method for short) is a scalar multiplication method for elliptic curve cryptography (ECC). In WAP WTLS [49], SEC 2 [44], ANSI X9.62 [1] and X9.63 [2], several domain parameters for applications of the GLV method are described. Curves with those parameters have efficiently-computable endomorphisms. Recently the GLV method for Jacobians of hyperelliptic curve (HEC) has also been studied. In this paper, we discuss applications of the GLV method to curves with real multiplication (RM). It is the first time to use RM for efficient scalar multiplication as far as we know. We describe the general algorithm for using such RM, and we show that some genus 2 curves with RM have enough effciency to be used in the GLV method as in the previous CM case. Moreover, we will see that such RM curves can be obtained abundantly unlike the previously proposed CM curves of genus 2.

This paper presents the design of low-power low-noise 10 GHz CMOS monolithic integrated LC VCOs suitable for data clock recovery architectures in optical receivers of SDH (STM-64) and SONET (OC-192). Optimizations of device parameters and passive components are given in detail. For passive components, differential and single-ended inductor structures as well as MOS varactors with and without lightly doped drain/source (LDD) implantation have been investigated. The VCOs implemented in a 0.18 µm process demonstrate the single-side-band phase noise of as low as -107 dBc/Hz at 1 MHz offset and 21% tuning range while consuming only 7 mW under 1.8 V supply.

In this paper, a novel projection-based method is presented to register partial 3D point clouds, acquired from a multi-view camera, for 3D reconstruction of an indoor scene. In general, conventional registration methods for partial 3D point clouds require a high computational complexity and much time for registration. Moreover, these methods are not robust for 3D point cloud which has a low precision. To overcome these drawbacks, a projection-based registration method is proposed. Firstly, depth images are refined based on both temporal and spatial properties. The former involves excluding 3D points with large variation, and the latter fills up holes referring to four neighboring 3D points, respectively. Secondly, 3D point clouds acquired from two views are projected onto the same image plane, and two-step integer mapping is applied to search for correspondences through the modified KLT. Then, fine registration is carried out by minimizing distance errors based on adaptive search range. Finally, we calculate a final color referring to the colors of corresponding points and reconstruct an indoor scene by applying the above procedure to consecutive scenes. The proposed method not only reduces computational complexity by searching for correspondences on a 2D image plane, but also enables effective registration even for 3D points which have a low precision. Furthermore, only a few color and depth images are needed to reconstruct an indoor scene. The generated model can be adopted for interaction with as well as navigation in a virtual environment.

Mobile agent technology is applied to enhance the remote network management of large-scale networks, and real-world oriented entertainment systems, and so forth. In order to communicate, the agents exchange messages mutually and migrate repeatedly among terminals. Although these systems efficiently accomplish the tasks by using a large quantity of mobile agents, they have a serious problem in that the number of messages between agents increases in proportion to the square of the number of agents. These systems have to reduce the communication costs, such as the number of hosts relaying messages; however, the conventional message-delivering schemes alone cannot keep the communication costs to a minimum under all conditions. To minimize the communication costs, we propose a hybrid message-delivering scheme which dynamically selects the optimal message-delivering schemes. Firstly, we evaluate the communication costs of conventional schemes, and we design the hybrid message-delivering scheme. Then we perform simulation evaluations to derive the threshold value for switching a scheme to minimize the communication costs.

To achieve both of a high peak performance and low average power characteristics, frequency-voltage cooperative control processor has been proposed. The processor schedules its operating frequency according to the required computation power. Its operating voltage or body bias voltage is adequately modulated simultaneously to effectively cut down either switching current or leakage current, and it results in reduction of total power dissipation of the processor. Since a frequency-voltage cooperative control processor has two or more operating frequencies, there are countless scheduling methods exist to realize a certain number of cycles by deadline time. This proposition is frequently appears in a hard real-time system. This paper proves two important theorems, which give the power-minimum frequency scheduling method for any types of frequency-voltage cooperative control processor, such as Vdd-control type, Vth-control type and Vdd-Vth-control type processors.

In this paper a straight-forward approach to extract the equivalent loop-gain of a continuous time Delta-Sigma modulator with an arbitrary DAC waveform in z-domain is presented. In this approach the arbitrary DAC waveform is approximated by the infinite number of rectangular pulse shapes. Then simply using the transformations available in literatures for a rectangular DAC pulse shape and applying superposition on each rectangular pulse shape, the loop-gain of the system is derived in z-domain.

Bluetooth is reputed as a wireless networking technology capable of forming ad-hoc networks between digital devices. In particular, the Bluetooth scatternet will be an essential part of the fully distributed ad-hoc networks. However, scatternet is not fully described in the Bluetooth specification. This has been the topic of discussion among researches in relation to the formation algorithm, scheduling scheme, etc. Most of the proposed algorithms reported in past researches on scatternet formation are too large and complex to be implemented in a real commercial Bluetooth hardware. Therefore, the verifications of the proposed algorithms reported in past researches were done through only simulations. In addition, the formation process takes too long and these past researches had been conducted only in static environment where no node enters or leaves the scatternet. In this paper, therefore, we propose a new scatternet formation algorithm called Node Ring Scatternet (NRS), emphasizing on two aspects, i.e. implementation and dynamic property of the algorithm. The algorithm is very simple and compact and is verified to be easily implementable in a real commercial Bluetooth device. For the dynamic properties, the NRS entails relatively short formation delay and a reformation algorithm in a dynamic environment was designed. Therefore, the network of the NRS can be scalable and flexible. In addition, a new protocol called SFMP (Scatternet Formation & Management Protocol) was designed and is presented herein. Using this protocol, the NRS algorithm was implemented in a real Bluetooth device, and the performance was verified through hardware experiments. Based on the experimental results, it was found that the NRS composed of up to 20 nodes is formed and the proposed algorithm has shown improvement in terms of formation delay, formation probability and reformation.

An inverse scattering problem of estimating the surface impedance for an inhomogeneous half-space is investigated. By virtue of the fact that the far field representation contains the spectral function of the scattered field, complex values of the function are estimated from a set of absolute values of the far field. An approximate function for the spectral function is reconstructed from the estimated complex values by the least-squares sense. The surface impedance is estimated through calculating the field on the surface of the half-space expressed by the inverse Fourier transform. Numerical examples are given and the accuracy of the estimation is discussed.