Novel design concept of waveguide mode adapter for low-loss modeconversion

We proposed a novel design concept of a mode adapter using a new parameter. The overlap integration of two adjacent mode profiles is defined as a single step loss (SSL) parameter for the characterization of optical mode confinement as well as the quantification of mode mismatch. The variation of SSL is described with two parameters. These parameters are V, a normalized frequency, and s, a differential width variation ratio. The contour for constant SSL in the V, s plane provides the optimized s curve as a function of V. The design concept with this constant SSL is shown to provide optimized adapters of minimized conversion loss     

Mode‐SVD‐Based Maximum Likelihood Source Localization Using Subspace Approach

A mode‐singular‐value‐decomposition (SVD) maximum likelihood (ML) estimation procedure is proposed for the source localization problem under an additive measurement error model. In a practical situation, the noise variance is usually unknown. In this paper, we propose an algorithm that does not require the noise covariance matrix as a priori knowledge. In the proposed method, the weight is derived by the inverse of the noise magnitude square in the ML criterion. The performance of the proposed method outperforms that of the existing methods and approximates the Taylor‐series ML and Cramér‐Rao lower bound.     

Graceful Degradation FEC Layer for Multimedia Broadcast/Multicast Service in LTE Mobile Systems

This paper proposes an additional forward error correction (FEC) layer to compensate for the defectiveness inherent in the conventional FEC layer in the Long Term Evolution specifications. The proposed additional layer is called a graceful degradation (GD)‐FEC layer and maintains desirable service quality even under burst data loss conditions of a few seconds. This paper also proposes a non‐delayed decoding (NDD)‐GD‐FEC layer that is inherent in the decoding process. Computer simulations and device‐based tests show a better loss recovery performance with a negligible increase in CPU utilization and occupied memory size.     

Effect of tap spacing on the performance of direct-sequencespread-spectrum RAKE receiver

The effect of tap spacing on the performance of a RAKE receiver is analyzed analytically in a frequency-selective fading channel. A continuous time multipath fading channel model is used for the analysis, and the expression of the correlation between the desired signals, interference signals, and noise signals at the output of each branch of the RAKE receiver is derived for various chip waveforms. Since the noise components of each branch signal are correlated to each other, an optimum combining rule based on the maximum-likelihood criterion is derived to gain utmost performance. It is shown that the performance of the system can be improved by setting the tap spacing of the RARE receiver below the chip duration when the bandwidth of the transmitted signal is larger than the inverse of the chip duration. Also, it is shown that the normalized capacity of the system can be increased by using a chip waveform occupying wider bandwidth, which takes advantage of the increased diversity gain merits of a wide-band code-division multiple-access system at the same chip rate. It is noted that the derived combining rule gives diversity gain against the fading process as well as noise whitening processing gain against multiple-access interference at the same time     

Hybrid pulse position modulation/ultrashort light pulse code-division multiple-access systems .I. Fundamental analysis

We propose a hybrid pulse position modulation/ultrashort light pulse code-division multiple-access (PPM/ULP-CDMA) system for ultrafast optical communications. The proposed system employs spectral CDMA encoding/decoding and PPM with very short pulse separation. The statistical properties of the encoded ULP are investigated with a general pulse model, and the performance of the proposed PPM/ULP-CDMA system is investigated. It is shown that we can improve upon the performance of other ULP-CDMA systems, such as those using on-off keying, by employing PPM. It is also shown that we can improve the performance of the proposed system by increasing the effective number of chips, by increasing the number of PPM symbols, and by reducing the ULP duration. The performance analysis shows that the aggregate throughput of the proposed PPM/ULP-CDMA system could be over 1 Tb/s.     

Low Voltage CMOS LC VCO with Switched Self‐Biasing

This paper presents a switched self‐biasing and a tail current‐shaping technique to suppress the 1/f noise from a tail current source in differential cross‐coupled inductance‐capacitance (LC) voltage‐controlled oscillators (VCOs). The proposed LC VCO has an amplitude control characteristic due to the creation of negative feedback for the oscillation waveform amplitude. It is fabricated using a 0.13 µm CMOS process. The measured phase noise is ‐117 dBc/Hz at a 1 MHz offset from a 4.85 GHz carrier frequency, while it draws 6.5 mA from a 0.6 V supply voltage. For frequency tuning, process variation, and temperature change, the amplitude change rate of the oscillation waveform in the proposed VCO is 2.1 to 3.2 times smaller than that of an existing VCO with a fixed bias. The measured amplitude change rate of the oscillation waveform for frequency tuning from 4.55 GHz to 5.04 GHz is 131 pV/Hz.     

Computer-aided diagnosis of solid breast nodules: use of an artificial neural network based on multiple sonographic features

A computer-aided diagnosis (CAD) algorithm identifying breast nodule malignancy using multiple ultrasonography (US) features and artificial neural network (ANN) classifier was developed from a database of 584 histologically confirmed cases containing 300 benign and 284 malignant breast nodules. The features determining whether a breast nodule is benign or malignant were extracted from US images through digital image processing with a relatively simple segmentation algorithm applied to the manually preselected region of interest. An ANN then distinguished malignant nodules in US images based on five morphological features representing the shape, edge characteristics, and darkness of a nodule. The structure of ANN was selected using k-fold cross-validation method with k = 10. The ANN trained with randomly selected half of breast nodule images showed the normalized area under the receiver operating characteristic curve of 0.95. With the trained ANN, 53.3% of biopsies on benign nodules can be avoided with 99.3% sensitivity. Performance of the developed classifier was reexamined with new US mass images in the generalized patient population of total 266 (167 benign and 99 malignant) cases. The developed CAD algorithm has the potential to increase the specificity of US for characterization of breast lesions.     

Anomaly detection in particulate matter sensor using hypothesis pruning generative adversarial network

The World Health Organization provides guidelines for managing the particulate matter (PM) level because a higher PM level represents a threat to human health. To manage the PM level, a procedure for measuring the PM value is first needed. We use a PM sensor that collects the PM level by laser-based light scattering (LLS) method because it is more cost effective than a beta attenuation monitor-based sensor or tapered element oscillating microbalance-based sensor. However, an LLS-based sensor has a higher probability of malfunctioning than the higher cost sensors. In this paper, we regard the overall malfunctioning, including strange value collection or missing collection data as anomalies, and we aim to detect anomalies for the maintenance of PM measuring sensors. We propose a novel architecture for solving the above aim that we call the hypothesis pruning generative adversarial network (HP-GAN). Through comparative experiments, we achieve AUROC and AUPRC values of 0.948 and 0.967, respectively, in the detection of anomalies in LLS-based PM measuring sensors. We conclude that our HP-GAN is a cutting-edge model for anomaly detection.     

Electron Holography Studies on Narrow Magnetic Domain Walls Observed in a Heusler Alloy Ni50Mn25Al12.5Ga12.5

Peculiar magnetic domain walls produced in Heusler alloys, which have attracted renewed interest due to their potential application to actuators and spintronic devices, are studied here using electron holography. The observations reveal unexpectedly narrow magnetic domain walls, the width of which showed perfect agreement with that of the antiphase boundaries (APB, e.g., only 3 nm). While the results can be explained by the significant depression of ferromagnetism due to the local chemical disorder, the electron phase shift indicates that ferromagnetic correlation still remains in the APB region.     

CdSe-sensitized inorganic–organic heterojunction solar cells: The effect of molecular dipole interface modification and surface passivation

CdSe-sensitized heterojunction solar cells composed of mesoscopic TiO₂/CdSe/P3HT (poly-3-hexylthiophene) were constructed, and the negative molecular dipole of 4-methoxybenzenethiol (MBT) and the ZnS passivation layer were used as interface modifiers to improve device performance. Through the interface modification between TiO₂/CdSe and P3HT using MBT and by ZnS surface passivation, the power conversion efficiency of the modified solar cell was greatly enhanced from 1.02% to 1.62% under 1 sun illumination.