A synchronization state can be observed in coupled circuits. Furthermore, an interesting synchronization state was confirmed in coupled time-delayed chaotic circuits. In this study, we propose novel coupled systems and investigate the synchronization state in coupled time-delayed chaotic circuits. The proposed coupling methods of time-delayed chaotic circuits depend on the attractor type. We focus on the relationships between the synchronization state and the coupling method. Moreover, we investigate the special coupling methods of time-delayed circuits in this study.

View full abstract

In our research, we propose a novel synchronization scheme based on noise-induced synchronization. We introduce natural environmental noise as an additive input noise to uncoupled nonlinear oscillators. The natural environmental noises in neighboring areas are cross-correlated, and we have already shown that limit-cycle oscillators can be synchronized by such cross-correlated noise. In this paper, we investigate the feasibility of the proposed natural synchronization scheme for the Rössler system, one of the chaotic oscillators. We first evaluate the synchronization performance by adding cross-correlated Gaussian noise, and we show the possibility of synchronizing the chaotic oscillators using the cross-correlated noise. We also introduce a real environmental noise, environmental sound data obtained at neighboring microphone devices, and we show that Rössler oscillators can be synchronized by such cross-correlated environmental noise. Our proposed synchronization method can be applied to intermittent communication. Accordingly, we evaluate the collision probability for the proposed synchronization method in intermittent communication. We introduce some cyclic interference sources and measure the probability of collision.

View full abstract

We are developing technology for camera systems to monitor humans using an intermittent-sensing scheme. In this system, to reduce power consumption, a CMOS image sensor is powered on and captures optical images when humans are detected using a low-power IR array sensor. A low-power analog front end (AFE) circuit that reads the small output voltage of an IR array sensor is required to create the system. Therefore, we examined the circuit for the IR array sensor using methods of a dual-slope integrating analog-to-digital converter (ADC). Consequently, a power reduction of approximately 83% compared with existing IR array sensor devices is expected. Another expected achievement is a battery life of about 12 months, which would be 4.7 times longer than that of the previous system using an existing IR array sensor device for the whole system.

View full abstract

This paper presents a Ternary Content Addressable Memory with Individuality (ITCAM), which has individuality for data retrieval that is caused by the manufacturing of each LSI. The results of the maskable search by the ITCAM are different for each LSI. The ITCAM was implemented on two FPGA chips and tested in practice. The characteristic evaluation results show that the mask value for each LSI and word is slightly different due to the manufacturing variations. The reproducibility of mask value was confirmed under certain conditions. The reproducibilities were 88%, 73%, and 32% for one FPGA chip (CHIP A) and 94%, 52%, and 47% for another (CHIP B) when the operating time of ITCAM is 8, 64, and 128 system clocks, respectively. Thus, the reported ITCAM is a promising solution for providing a little individuality to each LSI.

View full abstract

For many mathematical applications, the conventional coordinate rotation digital computer (CORDIC) algorithm can achieve high efficiency. However, the iterative procedure of the conventional CORDIC algorithm is inefficient owing to its rotation strategy. Chen et al. proposed a CORDIC algorithm with an improved rotation strategy to reduce the number of unnecessary iterations of the CORDIC algorithm. As a result, the calculation speed can be improved to four times than that of the conventional CORDIC hardware when the improved rotation strategy can finish its own functions within one clock cycle. However, the complexity of the improved rotation strategy is greatly increased, making it difficult to finish each rotation within one clock cycle. To overcome this difficulty, a hardware architecture for CORDIC with an improved rotation strategy is proposed to ensure that the improved rotation strategy can be finished within one clock cycle.

View full abstract

Given an undirected weighted graph G = (V,E,c) and a set T, where V is the set of nodes, E is the set of edges, c is a cost function, and T is a subset of nodes called terminals, the Steiner tree problem in graphs is that of finding the subgraph of the minimum weight that connects all of terminals.
The Steiner tree problem is an example of an NP-complete combinatorial optimization problem [1]. Thus, approximate methods are usually employed for constructing the Steiner tree. In this study, the KMB algorithm [2], which is an efficient construction method for Steiner tree problems, is enhanced by considering edge betweenness [3]. The results of numerical simulations indicate that our improved KMB algorithm shows good performances for various types of benchmark Steiner tree problems.

View full abstract

We propose an artificial slime mould model (ASMM) inspired by the plasmodium of Physarum polucephalum (P. polucephalum). ASMM consists of plural slimes, and each slime shares energy via a tube with neighboring slimes. Outer slimes sense their environment and conform to it. Outer slimes periodically transmit information about their surrounding environment via a contraction wave to inner slimes. Thus, ASMM shows how slimes can sense a better environment even if that environment is not adjacent to the slimes. The slimes subsequently can move in the direction of an attractant.

View full abstract

We have proposed a firefly algorithm that distinguishes between males and females. In this algorithm, both males and females exist. In this study, we investigate the features of our proposed algorithm by changing the parameters and the percentage of females. We compare our proposed firefly algorithm with the conventional firefly algorithm using four well-known test functions. Numerical experiments indicate that our proposed firefly algorithm is superior to the conventional firefly algorithm under some conditions.

View full abstract

To detect abnormal price jumps of financial markets, some indicators based on volatility have been used such as the bipower variation and the BPV ratio. However, these indicators only focus on a single individual stock and do not consider　the　relationships among　all　individual　stocks　composing a complex financial system. For this reason, we applied an autoencoder to learn the relationships among all stocks, and we considered a stock price that the autoencoder cannot restore as an abnormal price. Moreover, we identified that the price movement immediately following an abnormal price is clearly biased, and we confirmed the validity of our trading strategy based on this anomaly by performing some statistical significance tests.

View full abstract

To solve m-objective k-knapsack problems (mk-KPs) by using evolutionary algorithms, we propose a repair method that transforms infeasible solutions into feasible ones. In evolutionary multi-objective optimization, each solution in the population has a role in approximating a part of the Pareto front. However, since the conventional weighted scalar repair method (WSR) does not consider the position of each solution in the objective space, the solution diversity to approximate a wide range of the Pareto front is deteriorated. To improve the search performance of evolutionary algorithms for solving mk-KPs by enhancing the diversity of solutions, we propose a repair method considering the positions and repair directions of infeasible solutions in the objective space. Experimental results show that the proposed method improves the diversity of solutions and achieves higher search performance than the conventional WSR in mk-KPs.

View full abstract

In this paper, optical wireless turbo-coded on-off-keying (OOK) systems have been investigated. These systems suffer from performance deterioration due to background noise and the occurrence of synchronization slip. To solve these problems, an optical wireless system that combines a framed differential OOK (framed-DOOK) system and a punctured turbo-coded system is proposed. The bit error rate (BER) performance ef the punctured turbo-coded framed-DOOK system is evaluated in an optical wireless channel. It is shown that the punctured turbo-coded framed-DOOK system can greatly improve the BER performance of the conventional punctured turbo-coded OOK system. Moreover, in the framed-DOOK systems, the BER of the punctured turbo-coded system is almost the same as that of the standard turbo-coded system. Therefore, the proposed punctured turbo-coded framed-DOOK system is more attractive than the conventional turbo-coded OOK systems for optical wireless communications.

View full abstract

In this paper, improved code-shift keying (CSK) systems with a functional pseudonoise (PN) code are considered for use in indoor optical-wireless channels. In CSK, increasing the number of optical PN codes improves the data rate. It is also effective for increasing the number of simultaneously transmitting optical PN codes. This method is named N-parallel CSK (N-CSK), which indicates the transmission of N codes. In order to enhance the data rate of CSK systems, optical PN code design has become one of the key areas of study. As such functional codes, in this paper we consider EPOM and POEPC, which can be generated by fusing two kinds of optical PN codes. CSK systems can implement two-stage demodulation, which demodulates every optical PN code. It is expected that two-stage demodulation will improve the bit error rate (BER) performance of CSK systems. In this paper, we combine two-stage demodulation with CSK systems: CSK using EPOM and N-CSK using POEPC. It was found that the BER of CSK systems can be improved by utilizing two-stage demodulation.

View full abstract

Underwater wireless optical communication (UWOC) can provide higher-data-rate communication over moderate distances for new underwater applications. However, high-speed data transmission in UWOC is mainly limited by spectral attenuation in water and background noise. In this study, we propose an analytical underwater daylight noise model that incorporates the daylight simulation model SPCTRAL2 with an upwelling solar radiance model for the practical analysis of background light for UWOC. Moreover, we also consider a differential on-off-keying (DOOK) system in our simulation model. This DOOK system was proposed to reduce the effect of background noise in free-space optical communications. It was found that the effectiveness of the DOOK system can be verified by our new underwater daylight noise model. For example, for coastal water and harbor water, the DOOK system can improve BERs compared with an OOK system with a fixed threshold. In addition, the DOOK system can achieve a BER of less than10⁻⁶ in coastal water during daylight hours.

View full abstract

We previously proposed a bilevel quadrature-modulation (QM) envelope-pulse-width-modulation (EPWM) transmitter using half a side of a trilevel EPWM architecture. However, the optimum relationship between the ΔΣ modulation (DSM) sampling frequency (fs), the interleaving frequency (fi) and the carrier frequency (fc) for a bilevel QM EPWM transmitter has not been investigated. This paper presents this optimum relationship, with the error vector magnitude (EVM) and the coding efficiency (CE) as figures of merit (FOMs).

View full abstract

Modulation classification is a key technology in current wireless communication systems. The technology is used to find the modulation employed or estimate channel state information (CSI). In this paper, a modulation classification method is proposed for phase shift keying (PSK) and quadrature amplitude modulation (QAM) under an unknown signal-to-noise ratio (SNR) condition. The method works without carrier synchronization and is based on likelihood estimation using the probability density function (pdf) of the received signal envelope. The superior classification error rate of the proposed method is demonstrated by computer simulations.

View full abstract

In this paper, we propose a simple method for the safe teleoperation of a three-parallel-crawler-type mobile robot with distance range sensors and a wireless camera having a fisheye lens. The method enables the robot to avoid collision when a distant operator manipulates the robot by viewing a streaming video. In addition, notifications of danger are shown on the control interface screen and an audible alarm informs of the risk of collision by using information obtained from distance-measuring sensors. The validity of this system was evaluated during on the basis of experimental results for the effectiveness the sensors during operation.

View full abstract

This paper proposes a power control algorithm for our previously reported joint control method for autonomous cell association and transmission power control of pico-base stations (BSs) in heterogeneous networks with intercell interference coordination (ICIC), where low transmission-power pico-BSs are overlaid onto a high transmission-power macro-BS. We previously proposed a two-step power control algorithm whose calculation complexity is relatively low. However, the algorithm does not necessarily find the optimal solution for the given problem. Therefore, in this paper, we propose an iterative power control algorithm that always finds the optimal solution and compares the algorithm to the previous one. Based on numerical results, we show that the new optimal algorithm achieves a higher geometric mean user throughput than the previous one. However, we also show that the throughput gain is small and the previous algorithm achieves a higher geometric mean user throughput than the optimal one when we assume the same computational complexity.

View full abstract

To investigate the relationships between speech perception and production, speaking styles and performances of speakers have been investigated during speech production under delayed auditory feedback (DAF). However, previous studies have focused on only the delay in feedback for air-conducted speech although speakers perceive their own voice for both air-conducted and bone-conducted speech. In this paper, the phenomena between speech production and perception were investigated under DAF presented as both air-conducted and bone-conducted speech. It was then confirmed whether the speaking styles and performances were similar or different for these two types of presentation. The ratio of speech duration under delay conditions to that under a non-delay condition (Rd) and the number of dysfluent episodes (Nd) were measured to quantify the effect of delayed speech on the speaking styles and performances. As a result, long duration and several dysfluencies were observed under DAF for both air-conducted and bone-conducted presentation. Moreover, the changes under DAF for bone-conducted presentation tended to be larger than those for air-conducted presentation. These results suggest that the effect of delay in feedback due to bone-conducted speech might be stronger than that due to air-conducted speech.

View full abstract

The concept of the modulation transfer function (MTF) is usually used to not only restore the power envelope of reverberant speech but also to predict speech intelligibly in reverberant environments. The generalized room impulse response (RIR) has been proposed to mathematically model real reverberant environments. However, infinite impulse response (IIR) filters of generalized RIRs have not yet been designed from the corresponding MTF and inverse MTF (IMTF) due to the generalized RIR complexity of mathematical derivations. This paper derives the IIR implementation of the MTF and IMTF by using the impulse invariant method and bilinear transformation. Simulations were carried out to evaluate the two types of the derived IIR filters of the MTF and IMTF. It was found that the derived IIR filters with the impulse invariant method are more suitable than those by bilinear transformation.

View full abstract

Hidden Markov model (HMM)-based synthesized voices are intelligible but not natural especially under limited-data conditions due to over-smoothed speech spectra. Improving naturalness is a critical problem of HMM-based speech synthesis. One solution is to use voice conversion techniques to convert over-smoothed spectra to natural spectra. Although conventional conversion methods transform speech spectra to natural ones to improve naturalness, they cause unexpected distortions in the intelligibility of synthesized speech. The aim of the study is to improve naturalness without reducing the intelligibility of synthesized speech by employing our novel asymmetric bilinear model (ABM) to separate the intelligibility and naturalness of synthesized speech. In the study, our ABM was implemented on the modulation spectrum domain of Mel-cepstral coefficient (MCC) sequences to enhance the fine structure of spectral parameter trajectory generated from HMMs. Subjective evaluations carried out on English data confirmed that the achieved naturalness of the method using the ABM involving singular value decomposition (SVD) was competitive with other methods under large-data conditions and outperformed other methods under limited-data conditions. Moreover, modified rhyme test (MRT) showed that the intelligibility of synthesized speech was well preserved with our method.

View full abstract

In this paper, we investigate loudspeaker array directivity control and its application to sound localization when steering the beam direction of the loudspeaker array. The filter of a spherical loudspeaker array is designed based on the minimum variance (MV) method [1] in the spherical harmonics (SH) domain [2]. The beam pattern generated by the filter achieves a high directivity in a certain direction. Further, the beam direction can be rotated while maintaining the shape of the beam pattern. We implemented a prototype system that allows the listener to steer the beam direction using a gyro sensor in real time. The listening test result suggested that the location of the sound image varies based on the sound reflected from the wall. We evaluated the sound localization mechanism while rotating the beam direction based on the observed signal measured with a dummy head. The result showed that the sound of the beam reflected from a wall influences horizontal plane localization and sound image distance.

View full abstract

In order to remove zoom blurring caused due to the movement of the endoscope in the depth direction, it is necessary to obtain the point spread function (PSF) from the degraded image. However, the PSF of a zoom-blurred image has not been clearly modeled because zoom blurring depends on the position of the image. In this study, we propose a method to estimate the PSF of a zoom-blurred image and conduct a fundamental experiment to confirm its validity.

View full abstract

This paper proposes an effective noise reduction approach for retinal tomography. Tomographic images include many speckle and impulse noises. The conventional approach removes them by averaging ten or more continuous shots in a second. However, the averaging often causes a blur or disappearance of the diseased part because patient's eyeball moves in three dimensions during the continuous shooting. This paper proposes a new approach based on locally weighted averaging to reduce noise while being diagnosed. Results of the comparative experiments have shown that the proposed approach can hold the feature of the diagnosis part, while the conventional approach loses it.

View full abstract

In this paper, we propose an automatic diagnosis system for abnormal respiratory sound using a divided pulmonary sound waveform. Our method is based on a principal component analysis-linear discriminant analysis (PCA-LDA) discriminator using spectrogram features of an expiration waveform. The discrimination accuracy of the system was examined in simulations. The sensitivity and specificity of healthy against pathological discrimination and the symptom discrimination accuracy were improved compared with a mel-frequency cepstrum coefficients-Gaussian mixture model (MFCC-GMM)-based method. Computational efficiency was also improved.

View full abstract