Joohee Moon

Peak-to-average power control for multiple-antenna HIPERLAN/2 and IEEE802.11a systems

A combination of multi-input multi-output (MIMO) signal processing with orthogonal frequency division multiplexing (OFDM) is regarded as a promising solution for enhancing the performance of next generation wireless local area network (WLAN) systems. This paper evaluates the peak-to-average power ratio (PAR) performance in a MIMO OFDM-based WLAN system using a space-time block code (STBC). The investigated PAR control schemes, which are originally based on the selective mapping (SLM) and partial transmit sequence (PTS) approaches, select the transmitted sequence with the lowest average PAR over all transmit antennas and retrieve the side information (SI) very accurately at the expense of a slight degradation of the PAR performance. The low probability of false SI can improve the overall detection performance of the MIMO-WLAN system encountered with erroneous SI compared to the ordinary SLM and PTS approaches, respectively.

Rate Control for Consistent Objective Quality in High Efficiency Video Coding

Since video quality fluctuation degrades the visual perception significantly in multimedia communication systems, it is important to maintain a consistent objective quality over the entire video sequence. We propose a rate control algorithm to keep the consistent objective quality in high efficiency video coding (HEVC), which is an upcoming standard video codec. In the proposed algorithm, the probability density function of transformed coefficients is modeled based on a Laplacian function that considers the quadtree coding unit structure, which is one of the characteristics of HEVC. In controlling the video quality, distortion-quantization and rate-quantization models are derived by using the Laplacian function. Based on those models, a quantization parameter is determined to control the quality of the encoded frames where the fluctuation of video quality is minimized and the overflow and underflow of buffer are prevented. From the simulation results, it is shown that the proposed rate control algorithm outperforms the other conventional schemes.

A new vertex-based binary shape coder for high coding efficiency

Abstract This paper proposes a new vertex-based binary shape intra coding scheme that generates a set of vertices reducing shape reconstruction error and efficiently encodes the vertices. The conventional vertex-based coding scheme uses the iterated refinement method (IRM) for vertex selection and the object-adaptive vertex encoding (OAVE) for vertex transmission. In the proposed scheme, we introduce a vertex adjustment method to be applied to the vertices selected by the IRM. The vertex adjustment method significantly reduces the reconstruction error of binary shapes. For efficient transmission of vertices, we also propose 1D vertex detection, vertex reordering and initial vertex encoding methods. Furthermore, a conditional differential chain coding is presented for efficient lossless coding of contours. Experimental results show that the proposed vertex-based intra coding scheme reduces coded bits by 17–29% compared with the conventional vertex-based coding scheme, and by up to 27% compared with the intra coding mode of the context-based arithmetic encoding (CAE) scheme of the MPEG-4 Video Verification Model.

Modified cubic convolution scaler for edge-directed nonuniform data

We derive a modified version of the cubic convolution scaler to enlarge or reduce the size of digital images with arbitrary ratio. To enhance the edge information of the scaled image and to obtain a high-quality scaled image, the proposed scaler is applied along the direction of an edge. Since interpolation along the direction of an edge has to process nonuniformly sampled data, the kernel of the cubic convolution scalar is modified to interpolate the data. The proposed scaling scheme can be used to resize pictures in various formats in a transcoding system that transforms a bit stream compressed at one bit rate into one compressed at another bit rate. In many applications, such as transcoders, the resolution conversion is very important for changing the image size while maintaining high quality of the scaled image. We show experimental results that demonstrate the effectiveness of the proposed interpolation method. The proposed scheme provides clearer edges, without artifacts, in the resized image than do conventional schemes. The algorithm exhibits significant improvement in the minimization of information loss when compared with the conventional interpolation algorithms.

BER performance of multiple-antenna OFCDM with imperfections

This letter investigates the performance degradation due to the imperfect parameters in orthogonal frequency- and code-division multiplexing (OFCDM) systems with multiple antennas. For the performance evaluation, the average bit error rate (BER) expression is generalized to the multiple-antenna case in the presence of the channel estimation error and frequency offset. Derived results show that the multiple-antenna OFCDM systems experience a severe BER degradation regardless of the number of users.

Frame Bit-rate Control Method for Low Delay Video Communication

As the real time multimedia service become more popular, the needs of transmission with low delay and high quality are getting more stronger. Among those video compression technologies, the rate control method dose an important role in getting the effective data transmitting and the high image quality. In this paper, we combined the feature of CBR and VBR coding methods to propose a new bit-rate control method witch allows each frame to generates bits in the defined fluctuation range and applies a scene change detection at a part of frame and also can maintain low-delay and high quality even if the perfect VBR transmission environment is not guaranteed. The experiment result shows the proposed algorithm provides more effective method than TMN8 in real time application.

Adaptive weighted prediction based on moving area extraction and local brightness variation detection

In this paper, an adaptive weighted prediction is proposed to improve the coding efficiency. Conventional weighted prediction methods are optimized for specific sequences with global brightness variations (GBVs) such as fade-in and fade-out. However, if there is uncovered background by motion between current picture and reference picture, weighted prediction parameter (WPP) could not be derived accurately. And if there are local brightness variations (LBVs) between the pictures, it is not efficient to derive WPP over the entire picture. In order to solve above-mentioned problems, two kinds of technologies are added on conventional weighted prediction. First, moving area extraction (MAE) technology is devised to classify a picture into moving area and background area, and then two sets of WPP are derived for each area. Secondly, local brightness variation detection (LBVD) technology is added to detect the area including LBVs, and then the third set of WPP is derived for the detected LBV area. The proposed scheme is implemented on the HEVC Reference Software HM 10.0, and shows that maximum coding efficiency gain is up to 11.0% in luminance.

Fast Fine Granularity Scalability Decoding Scheme for Low-Delay Scalable Video Coding Applications

The Fine Grain Scalability (FGS) technique used in SVC codec encodes and decodes the quantization error of QBL (quality base layer) along the cyclic scanning path. The FGS technique provides the scalability property to the compressed bit stream. However, the cyclic scanning procedure of FGS method may require a huge computing time. In this paper, we propose a fast FGS decoding scheme, which has a lower decoding complexity without sacrificing image quality.

Techniques improving the transmission reliability in high-rate wireless LANs

This paper presents frame synchronization and two frequency synchronization techniques for high-rate wireless LANs (local area networks). Also, to improve the reliable communication under the multipath fading channel, we propose the wireless LAN system employing the space-time code. The proposed frame synchronization technique using the threshold checking scheme is directly based on the correlation method. We then describe a coarse frequency synchronization technique combining two conventional synchronization techniques to estimate an integral frequency-offset and a frequency synchronization technique employing interpolation method to estimate the integral and fractional frequency- offsets at the same time, respectively. Finally, by simulation, the performance of the proposed techniques is evaluated.

Weighted Prediction considering Global Brightness Variation and Local Brightness Variation in HEVC

In this paper, a new weighted prediction scheme is proposed to improve the coding efficiency for video scenes containing brightness variations. Conventional weighted prediction is applied by the reference picture and use only one weighted parameter set. Thus, it is only useful for GBV(Glabal Brightness Variation). In order to solve this problem, the proposed algorithm use three kind of schemes depending on situation. Experimental results show that maximum coding efficiency gain of the proposed method is up to 10.2% in luminance. Average computional time complexity is increased about 163% in encoder and about 101% in decoder. Keyword : HEVC, Weighted Prediction, GBV, LBV, Inter Prediction a) 세종대학교 정보통신연구소(Sejong University, Information and Telecommunication Research Institute) ‡Corresponding Author : 문주희(Joo-hee Moon) E-mail: jhmoon@sejong.ac.kr Tel: +82-2-3408-3829 ORCID: http://orcid.org/0000-0002-9055-9398 ※이 논문은 2015년도 정부(교육부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임(No. 2014R1A1A2055351). ・Manuscript received May 11, 2015; Revised July 9, 2015; Accepted July 9, 2015. 특집논문 (Special Paper) 방송공학회논문지 제20권 제4호, 2015년 7월 (JBE Vol. 20, No. 4, July 2015) http://dx.doi.org/10.5909/JBE.2015.20.4.489 ISSN 2287-9137 (Online) ISSN 1226-7953 (Print) 490 방송공학회논문지 제20권 제4호, 2015년 7월 (JBE Vol. 20, No. 4, July 2015)