Dual Decision Feedback Equalizer를 위한 LMS 알고리즘과 변형된 Steepest Descent 알고리즘이 결합된 새로운 적응 등화 알고리즘

공현윤,서성호 울산대학교 2001 공학연구논문집 Vol.32 No.1

Decision Feedback Equalizer(DFE)는 심한 심볼간 간섭이 존재하는 채널을 보상하는데 있어서 선형 등화기 보다 잡음 성분의 증폭이 적으므로 현재도 통신 시스템 및 하드 디스크 드라이브와 같은 자기 기록 장치의 채널 등화에 사용된다. 또한 최근에 동일한 구조의 DFE 두 개를 병렬로 사용하고 적은 메모리를 사용하여 성능을 향상시킨 Dual Decision Feedback Equalizer(DDFE)가 제안되었다. DDFE는 shift register를 사용하여 등화성능을 향상시킨 반면 시간 지연으로 인하여 Least Mean Square(LMS) 알고리즘과 같은 적응 등화 알고리즘을 적용하는데 어려움이 있다. 따라서 본 논문에서는 일반적으로 시불변 채널을 보상하는데 사용되는 DDFE가 시변 채널에 있어서도 효과적인 등화를 할 수 있도록 DDFE에 알맞은 등화 기법을 제안하였다. 컴퓨터 시뮬레이션을 통하여 본 논문에서 제안한 적응 등화 알고리즘이 LMS 알고리즘을 적용한 DFE와 대등한 성능을 가짐을 확인하였다. The Decision Feedback Equalizer(DFE) is one of currently used equalizers in communication and magnetic recording systems such as hard-disk drive since it can compensate for channels with severe inter-symbol interference(ISI) without as much noise enhancement as the linear equalizer(LE). To improve the performance of DFE, Dual Decision Feedback Equalizer(DDFE), which is constructed by using parallel combination of two DFEs and its performance is superior to the DFE, was suggested. However, DDFE is a preset equalizer which is used in a known channel. It is very difficult to make DDFE system applicable to unknown channel environment occurred in wireless communications. Because DDFE has shift registers which cause time delay. To make DDFE system applicable to unknown channel environments, we suggest proper adaptive equalization technique for the DDFE in this paper. Through computer simulation, we show that the proposed adaptive equalization technique for the DDFE is comparable to the performance of conventional LMS algorithm for DFE which doesn't have time delay.

3-차원 블록인터리버기법의 터보코드를 이용한 영상통신시스템설계

최태식,공형윤,최원호 울산대학교 2001 공학연구논문집 Vol.32 No.1

본 논문에서는 3-차원 블록인터리버기법의 터보코드를 사용하여 무선 통신 환경 하에서 효과적으로 전송할 수 있는 영상 통신 시스템을 제안한다. 웨이브릿 변환과 벡터양자화를 영상의 압축알고리즘에 사용하였으며, 무선통신시스템의 코딩방식 중 하나인 터보코드를 사용하여 압축영상데이터의 통신에 사용하였다. 터보코드의 성능은 데이터율, 부호기의 구속장의 길이, 복호 방식, 순환복호의 횟수, 인터리버의 종류 및 블록크기에 의존되어 진다. 같은 비트 크기에서의 2차원 블록인터리버보다 비트간의 거리를 크게 하는 3차원 인터리빙알고리즘을 적용한 시스템이 영상통신에서 높은 성능을 얻었다. 컴퓨터 시뮬레이션을 이용하여 3차원 블록인터리버의 성능을 압축된 영상과 가우시안 잡음 채널 환경 하에서 비교분석 하였다. In this paper, an image communication system that can effectively work in wireless communication environment is proposed. The wavelet transform and the vector quantization are used to the compress images. The turbo code that is one of the coding methods in wireless communication is used for the compressed image data communication. The efficiency of turbo code depends on the data rate, the constraint length, the decoding algorithm, the number of decoding iteration, the type of interleavers and the block size. The system with 3-D interleaving algorithm whose bit distance is longer than the 2-D block interleaver in the same size had the higher performance in image transmission. To verify the performance of the proposed method, computer simulation was performed in Gaussian noise model.

LDPC부호화를 적용한 영상통신시스템설계

최태식,공형윤,최원호 울산대학교 2001 공학연구논문집 Vol.32 No.1

다양한 멀티미디어 통신이 발달함에 따라 채널부호화를 사용하여 오류를 정정하는 기술이 발달되어 왔다. 본 논문에서는 압축영상의 전송에서 LDPC 부호화를 이용하여 영상통신채널에서의 오류를 복원하고, 영상을 재구성할 수 있는 영상통신시스템을 제안한다. 제안된 영상통신시스템은 패리티검사행렬을 사용하여 가장 많은 오류를 발생하는 열과 가장적은 오류를 발생하는 열을 교환하는 방식을 사용하였고, 가우시안 노이즈를 가지는 통신채널의 신호 대 잡음비는 0dB에서 4dB의 범위로 설정하였다. 패리티 검사 행렬이 작은 경우 제시한 교환 방식을 사용하였을 때 사용하지 않은 경우보다 BER 성능이 우수함을 확인하였으며, 영상을 재구성한 경우에도 PSNR 성능이 우수함을 확인할 수 있었다. As a various multimedia communication has been developed, the error correction technique using the coding method was improved. In this paper, an image communication system using the LDPC decoding method for restoring the error and reconstructing the image in the image compression transmission is proposed. The proposed system has a parity check matrix that can alternate the least occurring error column with the most occurring error column. The signal to noise ratio of a communication channel with the gaussian noise was determined the range between 0dB 4dB. When a parity check matrix was a small size, the system's BER efficiency with the parity check alternating method was better than the parity check without it. Also in reconstructing image, the proposed system's PSNR efficiency was superior to system without alternating method.

다이버시티 기법 및 콘볼루션코드를 이용한 영상통신 시스템 설계

장홍성,공형윤,최원호 울산대학교 2001 공학연구논문집 Vol.32 No.1

본 논문에서는 무선통신에 약한 압축영상의 품질을 개선할 수 있는 영상전송시스템을 구현하고자 한다. 무선 상에서 부호간 간섭과 다중경로 페이딩에 의한 채널의 영향을 줄이기 위하여 Decision Feedback Equalizer(DFE)와 다이버시티 기법을 적용하였고 연집에러에 대응하고자 콘볼루션부호와 인터리버를 사용하였다. 제안된 시스템의 성능분석을 위하여 세 가지 다이버시티 기술의 경우에 따라 성능분석을 하였으며, 다이버시티 기법과 콘볼루션 코드의 적용이 시스템의 향상된 성능을 나타내었다. In this paper, an image transmission system that can improve for the quality of a fragile compression image in wireless communication is designed. For reducing the channel effect of ISI(Inter-Symbol Interference) and multi-path fading in wireless transmission, DFE(Decision Feedback Equalizer) and diversity technique are adapted. And to minimize the burst error, the convolutional code and interleaver are implemented in the system. To analyze the performance of the system, the experiments were done with three types of diversity. The results show that the implementing of diversity technique and convolutional code can improve the performance of the system.

On the Outage Behavior of Interference Temperature Limited CR-MISO Channel

Kong, Hyung-Yun,Asaduzzaman, Asaduzzaman The Korea Institute of Information and Commucation 2011 Journal of communications and networks Vol.13 No.5

This paper investigates the outage behavior of peak interference power limited cognitive radio (CR) networks with multiple transmit antennas. In CR-multi-input single-output (MISO) channel, the total transmit power is distributed over the transmitantennas. First, we use the orthogonal space-time codes (STC) to achieve the transmit diversity at CR-receiver (rx) and investigate the effect of the power distribution on the interference power received at the primary-receiver (P-rx). Then, we investigate the transmit antenna selection (TAS) scheme in which the CR system selects the best transmit antenna and allocates all the power to the selected best antenna. Two transmit antenna selection strategies are proposed depending on if feedback channel is available or not. We derive the closed form expressions of outage probability and outage capacity of all schemes with arbitrary number of transmit-antennas. We show that the proposed schemes significantly improve the outage capacity over the single antenna systems in Rayleigh fading environment. We also show that TAS based scheme outperforms the STC based scheme when peak interference power constraint is imposed on the P-rx only if a feedback channel from CR-rx to CR-transmitter is available.

A Study for Reducing the PAPR in OFDM System

Hyung-Yun Kong(공형윤),Il-Seung Woo(우일승) 대한전자공학회 2000 대한전자공학회 학술대회 Vol.2000 No.6

M-Interval Detectors based on Quantized Noise Samples in Mobile Communications

Hyung-Yun Kong 한국정보과학회 1999 Journal of Electrical Engineering and Information Vol.4 No.2

A class of m-interval detectors based on the quantized noise sample space with posedetection dual diversity system is introduced. There are a lot of components which are corrupting the system caused by geographical features and a natural phenomenon and these interfering components are often radom but not gaussian. Due to unknown functional form of noise, it is not easy to design the detector through estimating the functional form of noise. Instead, we design the m-interval detectors by using the pure noise sample space which are partitioned by estimated quantiles in this paper. Since the m-interval detectors are susceptible to detect errors, the performance of the m-interval detectors is much better than that of other detectors. The detectors also operate at near optimum level for the underlying noise distributions and maintains its robustness in the changing intrinsic noise environments. Monte-Carlo simulation is used to show the performance of system suggested here compared to other systems.

무선통신에서의 Non-Linear Detector System 설계

Hyung Yun Kong 대한전자공학회 1998 대한전자공학회 학술대회 Vol.1998 No.6

The structure of equalizers based on quantized sample space with non-linear MMSE

Kong, Hyung-Yun The Korea Institute of Information and Commucation 1999 韓國通信學會論文誌 Vol.24 No.6

In this paper, were introduce two types of equalizers, called equalizer-a and equalizer-b, applying to wireless communications having unknown channel characteristics. The equalizer-a, which has the single sample detector with equalizer system, is developed while the equalizer-b has the partition detectors with the same system used in equalizer-a. The methodologiy we adopt for designing the equalizers is that the sample space is partitioned into finite number of regions by using quantiles, which are estimated by robbins-monro stochastic approximation (RMSA) algorithm, and the coefficients of equalizers are calculated based on nonlinear minimum mean, square error (MMSE) algorithm. Through the computer simulation, the equalizers show much better performance in equiprobably partitioned sample subspaces of observations than the single sample detector and the detector, which has the conventional equalizer, in unquantized observation space under various noise environments.

Long-term Fading Statistics-Based Power Allocation for Fixed Decode-and-Forward Relays

Hyung Yun Kong(공형윤),Vo Nguyen Quoc Bao(보 뉘웬 쿽 바오) 한국통신학회 2008 韓國通信學會論文誌 Vol.33 No.12A

This paper considers 2-hop wireless cooperative communications networks with fixed decode-and-forward relays. Specifically, we first derive the closed-form BER expression for theoretically evaluating the end-to-end performance of these networks. Then, based on this expression and long-term fading statistics, we propose a power allocation method for source and relay. Such a method brings about multiple advantages in term of spectral efficiency and implementation complexity over other power allocation methods based on instantaneous fading statistics. A variety of numerical results reveal that the cooperative communications scheme with the proposed power allocation significantly outperforms that with the equal power allocation and the direct transmission scheme for any position of the relay subject to the same total transmit power constraint.