Hyung-Myung Kim

Partial zero-forcing adaptive MMSE receiver for DS-CDMA uplink in multicell environments

Adaptive multi-user detection techniques for interference suppression in direct-sequence code division multiple access (DS-CDMA) systems have gained much attention since they do not require any information on interfering users. In the uplink of DS-CDMA systems, however, the base station receiver typically knows the spreading waveforms of the users within its cell but does not know those of the users in other cells. We propose a partial zero-forcing adaptive minimum mean squared error (MMSE) receiver for the DS-CDMA uplink utilizing the spreading waveforms known at the base station as well as training data. The proposed receiver first removes the intracell interference using a linear filter based on the knowledge of the spreading waveforms of the interfering users within the cell. Then the intercell interference remaining in the output of the linear filter is mitigated by adaptive MMSE detection. To speed up the convergence of the adaptive filter weights without loss of the steady-state performance, we develop a modified least mean square (LMS) algorithm based on the canonical representation of the filter weights. It is shown through analysis and simulation results that the proposed receiver improves the convergence speed and the steady-state performance.

Fabrication of LiMn2O4 thin films by sol–gel method for cathode materials of microbattery

Abstract LiMn2O4 thin films have received considerable attention as cathode materials for thin-film microbatteries. In this work, LiMn2O4 thin films are prepared by a sol–gel method using a spin coator. The precursor powder is investigated by TG–DTA and mass spectroscopy analysis in order to study the decomposition process prior to deposition. The coated films are dried at 310 to 360°C, and annealed at 700 to 800°C to obtain a spinel structure. Films annealed under appropriate conditions exhibit good crystallinity, smooth surface morphology, high capacity, and good rechargeability. This film is therefore suitable for use as a cathode for thin-film microbatteries.

Efficient camera motion characterization for MPEG video indexing

A novel approach to camera motion analysis is proposed to index videos compressed in MPEG-1 or MPEG-2. Specifically, it fits the motion vectors in the MPEG stream into the two-dimensional affine model to detect basic camera operations automatically. The proposed approach involves (1) the construction of motion vector fields (MVFs) by normalizing the types of motion vectors and filtering out noise; and (2) the qualitative interpretation of camera motions from the estimated model parameters in two levels (frame and temporal segment). Fine segmentation can also be obtained for a video, based on the homogeneity of camera motion in each unit. The advantages of our method lie in its computational efficiency and robustness to noisy environments such as false motion vectors and object motion. The proposed approach is validated by an experiment with real compressed video sequences.

The effect of grain size on dielectric behavior of BaTiO3 based X7R materials

Abstract Using high purity BaTiO 3 powders of various particle size, we investigated the temperature dependence of the dielectric constant in BaTiO 3 based X7R ceramic capacitor materials. The sintered grain size was almost proportional to the particle size of the starting BaTiO 3 powder. The sharp peak intensity at 130 °C and the broad peak intensity around the lower temperature were determined by the volume fraction of the grain cores and by the volume fraction of grain shells, respectively.

Utility-Based Video Adaptation for Universal Multimedia Access (UMA) and Content-Based Utility Function Prediction for Real-Time Video Transcoding

Many techniques exist for adapting videos to satisfy heterogeneous resource conditions or user preferences, whereas selection of the best adaptation operation among various choices usually is either ad hoc or inefficient. To provide a systematic solution, we present a conceptual framework based on utility function (UF), which models video entity, adaptation, resource, utility, and the relations among them. In order to support real-time video adaptation, we present a content-based statistical paradigm to facilitate the prediction of UF for real-time transcoding of live videos. Instead of modelling the UF through analytical models, as in the conventional rate-distortion framework, the proposed approach formulates the prediction as a classification and regression problem. Each video clip is classified into one of distinctive categories and then local regression is used to accurately predict the utility value. Our extensive experiment results based on MPEG-4 transcoding demonstrate that the proposed method achieves very promising performance - up to 89% accuracy in choosing the optimal transcoding operation (in both spatial and temporal dimensions) with the highest quality over a diverse range of target bit rates

A new resource allocation scheme based on a PSNR criterion for wireless video transmission to stationary receivers over Gaussian channels

A new resource allocation scheme is proposed for video service over a Gaussian channel. For video quality rating, we introduce a suitable metric: the average peak signal-to-noise ratio (PSNR) or the average channel-induced PSNR degradation. Then, we model the end-to-end distortion considering the error propagation effect caused by motion compensation. On the basis of this model, we propose an efficient resource allocation scheme for real video service. Unlike conventional schemes, the new scheme satisfies the PSNR requirement of each video user by adjusting the bit-error rate level with the changes of image characteristics. Simulation results show that the proposed scheme utilizes the bandwidth more efficiently than conventional schemes.

An optimum power management scheme for wireless video service in CDMA systems

An optimum power management scheme is proposed for intra-frame refreshed image sequences of the wireless video service in code-division multiple-access (CDMA) systems. The end-to-end distortion of H.263 video data is first modeled when the error concealment schemes are employed. This distortion model takes into account the error propagation effects caused by the motion compensation. Then, based on the model, the target bit-error rates (BERs) of the image frames are optimized in such a way that the consumed power could be minimized under the constraint of maximum distortion. To satisfy the specified target BER requirement, an optimum power management scheme is proposed. Simulation results show that the proposed scheme considerably outperforms the conventional scheme in the sense of the decoded image quality. Additionally, the effects of the imperfect power control on the performance are also investigated.

Precoder design of non-regenerative relays with covariance feedback

In this letter, the optimal form of the precoding matrix is initially derived to maximize the ergodic capacity between the source and destination with covariance information of the relay-destination link. The elements of the precoding matrix are then determined to maximize the upper bound of the ergodic capacity. The numerical results show that the performance of the proposed scheme is close to that of the full feedback scheme when there is a high correlation at the transmit antennas of the relay.

Summarization of news video and its description for content‐based access

A video summary abstracts the entirety with the gist without losing the essential content of the original video and also facilitates efficient content‐based access to the desired content. In this article, we propose a novel method for summarizing a news video based on multimodal analysis of the content. The proposed method exploits the closed caption (CC) data to locate semantically meaningful highlights in a news video and speech signals in an audio stream to align the CC data with the video in a time‐line. Then, the extracted highlights are described in a multilevel structure using the MPEG‐7 Summarization Description Scheme (DS). Specifically, we use the HierarchicalSummary DS that allows efficient accessing of the content through such functionalities as multilevel abstracts and navigation guidance in a hierarchical fashion. Intensive experiments with our prototypical systems are presented to demonstrate the validity and reliability of the proposed method in real applications.

Modified cubic convolution scaler with minimum loss of information

The authors derive an adaptive version of cubic convolution interpolation for the enlargement or reduction of digital images by arbi- trary scaling factors. The adaptation is performed in each subblock (typi- cally L3L rectangular) of an image. It consists of three phases: two scaling procedures (i.e., forward and backward interpolation) and an op- timization of the interpolation kernel. In the forward interpolation phase, from the sampled data with the original resolution, we generate scaled data with different (higher or lower) resolution. The backward interpola- tion produces new discrete data by applying another interpolation to the scaled one. The phases are based on a cubic convolution interpolation whose kernel is modified to adapt to local properties of the data. During the optimization phase, we modify the parameter values to decrease the disparity between the original data and those resulting from another in- terpolation on the different-resolution output of the forward interpolating phase. The overall process is repeated iteratively. We show experimen- tal results that demonstrate the effectiveness of the proposed interpola- tion method. The algorithm exhibits significant improvement in the mini- mization of information loss when compared with the conventional interpolation algorithms.