Software watermarking is a digital technique used to protect software by embedding some secret information as identification in order to discourage software piracy and unauthorized modification. Watermarking is still a relatively new field and has good potential in protecting software from privacy threats. However, there appears to be a security vulnerability in the watermark trigger behaviour, and has been frequently attacked. By tracing the watermark trigger behaviour, attackers can easily intrude into the software and locate and expose the watermark for modification. In order to address this problem, we propose an algorithm that obscures the watermark trigger behaviour by utilizing buffer overflow. The code of the watermark trigger behaviour is removed from the software product itself, making it more difficult for attackers to trace the software. Experiments show that the new algorithm has promising performance in terms of the imperceptibility of software watermark.

This paper is concerned with a method to reduce the computation time of the Discrete Ray Tracing Method (DRTM) which was proposed to numerically analyze electromagnetic fields above Random Rough Surfaces (RRSs). The essence of DRTM is firstly to search rays between source and receiver and secondly to compute electric fields based on the traced rays. In the DRTM, the method discretizes not only RRSs but also ray tracing procedure. In order to reduce computation time for ray searching, the authors propose to modify the conventional algorithm discretizing RRSs with equal intervals to a new one which discretizes them with unequal intervals according to their profiles. The authors also use an approximation of Fresnel function which enables us to reduce field computation time. The authors discuss the reduction rate for computation time of the DRTM from the numerical view points of ray searching and field computation. Finally, this paper shows how much computation time is reduced by the new method.

We propose a novel adaptive filtering scheme named metric-combining normalized least mean square (MC-NLMS). The proposed scheme is based on iterative metric projections with a metric designed by combining multiple metric-matrices convexly in an adaptive manner, thereby taking advantages of the metrics which rely on multiple pieces of information. We compare the improved PNLMS (IPNLMS) algorithm with the natural proportionate NLMS (NPNLMS) algorithm, which is a special case of MC-NLMS, and it is shown that the performance of NPNLMS is controllable with the combination coefficient as opposed to IPNLMS. We also present an application to an acoustic echo cancellation problem and show the efficacy of the proposed scheme.

In this paper, a new method is proposed for unsupervised speckle level estimation in synthetic aperture radar (SAR) images. It is assumed that fully developed speckle intensity has a Gamma distribution. Based on this assumption, estimation of the equivalent number of looks (ENL) is transformed into noise variance estimation in the logarithmic SAR image domain. In order to improve estimation accuracy, texture analysis is also applied to exclude areas where speckle is not fully developed (e.g., urban areas). Finally, the noise variance is estimated by a 2-dimensional autoregressive (AR) model. The effectiveness of the proposed method is verified with several SAR images from different SAR systems and simulated images.

In this paper, we consider the problem of partitioning a given collection of node sets into k collections such that the average size of collections is the largest, where the size of a collection is defined as the cardinarity of the union of the subsets contained in the collection. More concretely, we give an upper bound on the performance ratio of an approximation algorithm proposed by Abrams et al., which is known to have a performance ratio of at least 1-1/e≅0.6321 where e is Napier's constant. The proposed upper bound is 1-(2-d+1√2)d+1/2 for any d≥1 provided that k=o(n) which approaches to 0.75 as d increases.

This paper presents an analysis of radiation-induced clock-perturbation in phase-locked loop (PLL). Due to a trade-off between cost, performance, and reliability, radiation hardened PLL design need robust strategy. Thus, evaluation of radiation vulnerability is important to choose the robust strategy. The conventional evaluation-method is however based on brute-force analysis — SPICE simulation and experiment. The presented analysis result eliminates the brute-force analysis in evaluation of the radiation vulnerability. A set of equations enables to predict the radiation-induced clock-perturbation at the every sub-circuits. From a demonstration, the most vulnerable nodes have been found, which are validated using a PLL fabricated with 0.18µm CMOS process.

AC conversion has a huge variety of applications and so there are many ongoing research topics as in every type of power electronic conversion. New semiconductors allow the increase of the switching frequency fact that brings a whole new prospective improvement in converter's operation. Many other possible nonlinear operation regimes, including period doubling and chaotic oscillations, appear besides the conventional steady state operation. In this work, a nonlinear discrete-time model of an AC/AC buck type converter is proposed. A discrete time iterative map is derived to highlight the sensitive switching dynamics. The model is able to observe fast scale phenomena and short transient effects. It offers more information compared to other methods such as the averaging ones. According to Electro-Magnetic Compatibility (EMC) regulations, low wide-band noise is more acceptable than the high narrow-band, therefore the goal of this work is to spread the harmonic noise into a wide frequency spectrum which has lower amplitudes compared to the conventional comb-like spectrum with distinctive amplitudes at switching frequency multiples. Through the numerical and experimental consideration the converter can operate in a chaotic motion and the advantages of the performance improvement are also discussed.

This paper proposes a vanishing point-based road detection method. Firstly, a vanishing point is detected using a texture-based method proposed in a recent study. After that, a histogram is generated for detecting two road borders. The road area is defined as the region between the two road borders and below the vanishing point. The experimental results demonstrate that our method performs well in general road images.

Per-User Unitary Rate Control (PU2RC) performs poorly when the number of users is small and suffers from the sum-rate ceiling effect in the high signal-to-noise ratio (SNR) regime. In this paper, we propose a multimode transmission (MMT) strategy to overcome these inherent shortcomings of PU2RC. In the proposed MMT strategy, the transmitter finds out the optimal transmission mode and schedules users using each user's instantaneous channel quality information (CQI) parameters. First we assume that each user's CQI parameters are perfectly reported in order to introduce the proposed MMT strategy. Then we consider the quantization of CQI parameters using codebooks designed by the Lloyd algorithm. Moreover, we modify the CQI parameters to improve the system's robustness against quantization error. Finally, in order to reduce the quantization error, we design a hierarchical codebook to jointly quantize the modified CQI parameters by considering the correlation between them. Simulation results show that the proposed MMT strategy effectively overcomes the shortcomings of PU2RC and is robust against low quantization level of CQI parameters.

Biometric identification has recently attracted attention because of its convenience: it does not require a user ID nor a smart card. However, both the identification error rate and response time increase as the number of enrollees increases. In this paper, we combine a score level fusion scheme and a metric space indexing scheme to improve the accuracy and response time in biometric identification, using only scores as information sources. We firstly propose a score level indexing and fusion framework which can be constructed from the following three schemes: (I) a pseudo-score based indexing scheme, (II) a multi-biometric search scheme, and (III) a score level fusion scheme which handles missing scores. A multi-biometric search scheme can be newly obtained by applying a pseudo-score based indexing scheme to multi-biometric identification. We secondly propose the NBS (Naive Bayes search) scheme as a multi-biometric search scheme and discuss its optimality with respect to the retrieval error rate. We evaluated our proposal using the datasets of multiple fingerprints and face scores from multiple matchers. The results showed that our proposal significantly improved the accuracy of the unimodal biometrics while reducing the average number of score computations in both the datasets.

A promising application of a single-flux quantum (SFQ) circuit is read-out circuitry for a multi-channel superconductive sensor array. In such applications, the SFQ read-out circuit is expected to operate outside a magnetic shield. We investigated an SFQ circuit structure, which is tolerant to an external magnetic field, using the AIST 2.5kA/cm2 Nb standard 2 process, which has four Nb wiring layers including the ground plane. By covering the entire circuit using an upper Nb wiring layer called the control (CTL) layer, the influences of the external magnetic field on the SFQ circuit operation can be avoided. We experimentally evaluated the sheet inductance of the wiring layer underneath the CTL shielding layer to design a magnetic-field-tolerant SFQ circuit. We implemented and measured test circuits comprising toggle flip-flops (TFFs) to evaluate their magnetic field tolerances. The operating margin and maximum operating frequency of the designed TFF did not deteriorate with increases in the magnetic field applied to the test circuit, whereas the operating margin of the conventional TFF was reduced by applying the magnetic field. We have also demonstrated the high-speed operation of the designed TFF operated in an unshielded environment at a frequency of up to 120GHz with a wide operating margin.

In order to analyze an impact of threshold voltage (Vth) fluctuation induced by random telegraph noise (RTN) on LSI circuit design, we measured a 40-nm 6-Tr-SRAM TEG which enables to evaluate individual bit-line current. RTN phenomenon was successfully measured and we also identified that the transfer MOSFET in an SRAM bit-cell was the most sensitive MOSFET. The proposed word line boosting technique, which applies slightly extra stress to the transfer MOSFET, improves about 30% of detecting probability of fail-bit cells caused by RTN.

This paper presents the strategy of MOS varactor's high-Q optimization, a novel scalable model for the quasi-millimeter-wave MOS varactors, and confirmation results by discrete MOS varactors and VCO measurements. To realize a high-Q MOS varactor in the quasi-millimeter-wave region, low MOS varactor capacitance and low series resistance of unit cell are essential. Downsizing is a key to realize both low capacitance and low resistance. However, it is induced by Cmax/Cmin reduction, simultaneously. Therefore, scalable MOS varactor model is necessary to use optimum MOS varactor to cover various application requirements using same process. Decreasing the MOS varactor's size of W/L =2µm/2µm to 0.5µm/0.26µm, the Q factor increased sevenfold at f =20GHz but Cmax/Cmin is reduced by 60%, by using conventional PSP model, an error of approximately 20% is shown. Proposed model has been improved its accuracy from 18.9% to 0.2% for N+ MOS varactor and from 22.1% to 0.8% for P+ MOS varactor, for minimum size of MOS varactor even if model covers wide dimension range. Also, it has been confirmed this model is covered in two types of layouts. Oscillation frequency and phase noise also have been confirmed by three types of 22GHz VCOs. The accuracy of oscillation frequency is less than 2.5% and that of phase noise at 1MHz offset from carrier is less than 5dB.

In this paper, we study the impact of opportunistic user scheduling on the outage probability of cognitive radio (CR) multiple-input multiple-output (MIMO) systems in the high power region where the peak transmit power constraint is higher than the peak interference constraint. The primary contributions of this paper are the derivation of exact closed-form expressions of the proposed scheduled CR-MIMO systems for outage probability and asymptotic analysis to quantify the diversity order and signal to noise ratio (SNR) gain. Through exact analytical results, we provide the achievable outage probability of the proposed scheduled systems as a function of SNR. Also, through asymptotic analysis, we show that the scheduled CR-MIMO systems provide some diversity order gain over the non-scheduled CR-MIMO systems which comes from multi-user diversity (MUD). Also, the SNR gain of the proposed scheduled systems is identical to that of the non-scheduled CR-MIMO systems.

The single flux quantum (SFQ) is expected to be a next-generation high-speed and low-power technology in the field of logic circuits. CMOS as the dominant technology for conventional processors cannot be replaced with SFQ technology due to the difficulty of implementing feedback loops and conditional branches using SFQ circuits. This paper investigates the applicability of a reconfigurable data-path (RDP) accelerator based on SFQ circuits. The authors introduce detailed specifications of the SFQ-RDP architecture and compare its performance and power/performance ratio with those of a graphics-processing unit (GPU). The results show at most 1600 times higher efficiency in terms of Flops/W (floating-point operations per second/Watt) for some high-performance computing application programs.

One of the most important requirements for a routing protocol in wireless body area networks (WBANs) is to lower the network's temperature increase. The temperature of a node is closely related to its activities. The proactive routing approach, which is used by existing routing protocols for WBANs, tends to produce a higher temperature increase due to more frequent activities, compared to the on-demand reactive routing approach. In this paper, therefore, we propose a reactive routing protocol for WBANs called priority-based temperature-aware routing (PTR). In addition to lowering the temperature increase, the protocol also recognizes vital nodes and prioritizes them so they are able to achieve higher throughput. Simulation results show that the PTR protocol achieves a 50% lower temperature increase compared to the conventional temperature-aware routing protocol and is able to improve throughput of vital nodes by 35% when the priority mode is enabled.

Providing diverse Quality of Service (QoS) with ultra-low power consumption and support of mobility is the most important and challenging issue in wireless body area networks (WBANs). The IEEE 802.15.4 standard exhibits a desirable feature for WBAN, but its inability of mobility support makes it insufficient. In this paper, we show what is required for node mobility support and propose two strategies for the support. We observed that the amount of time required for the association process is the key reason IEEE 802.15.4 is unable to handle mobility. In this paper, we present a new fast association technique, which prevents nodes from scanning multiple channels. In the proposed scheme, by scanning just a single channel, a node can learn about all the coordinators working in different channels. The single channel scanning scheme is able to decrease the association time of IEEE 802.15.4 operating in 2.4GHz by 32 times. Furthermore, in this paper, a method to increase the node connectivity time with its coordinator in IEEE 802.15.4 beacon-enabled mode is introduced. The method tries to anticipate whether the node is moving towards or away from the coordinator by analyzing the signal strength of multiple beacons received from the same coordinator. Thus, the connectivity time is increased by choosing the coordinator with good signal strength, but located both furthest from the node and toward the direction which mobile node is moving. Our approach results in significant improvement by reducing the number of times the moving node switches coordinators. Experimental results have verified that our schemes work well in the mobile sensor network environment.

Space diversity reception is well known as a technique that can improve the performance of wireless communication systems without any temporal and spectral resource expansion. Implant body area networks (BANs) require high-speed transmission and low energy consumption. Therefore, applying spatial diversity reception to implant BANs can be expected to fulfill these requirements. For this purpose, this paper presents a local frequency offset diversity system with π/4-differential quadrature phase shift keying (DQPSK) for implant BANs that offer improved communication performance with a simpler receiver structure, and evaluates the proposal's bit error rate (BER) performance by theoretical analysis. In the theoretical analysis, it is difficult to analytically derive the probability density function (pdf) on the combined signal-to-noise power ratio (SNR) at the local offset frequency diversity receiver output. Therefore, this paper adopts the moment generating function approximation method and demonstrates that the resulting theoretical analyses yield performances that basically match the results of computer simulations. We first confirm that the local frequency offset diversity reception can effectively improve the communication performance of implant BANs. Next, we perform an analysis of a realistic communication performance, namely, a link budget analysis based on derived BER performance and evaluate the link parameters including system margin, maximum link distance and required transmit power. These analyses demonstrate that the local frequency offset diversity system can realize a reliable communication link in a realistic implant BAN scenario.

We have already proposed a service discovery scheme using mobile agents for mobile ad hoc networks where node positions in the network and the network topology change frequently. Mobile agents autonomously migrate among nodes and then perform a given task at a node. In the service discovery scheme using mobile agents, mobile agents collect and disseminate services in the network so it is most important how the mobile agents migrate in the network. Therefore, we propose two types of mobile agent migration mechanisms in this paper. One is that mobile agents migrate to the nodes at which other mobile agents do not stay, the other is that mobile agents migrate to the nodes to which mobile agents can disseminate a lot of service information. Finally, we conducted simulation experiments to investigate the performance of the proposed migration mechanisms with respect to the service dissemination time and rate.