• 전자공학회논문지B
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• 제31B권4호
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• pp.97-105
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• 1994

Transform image coding using DCT is proved to be efficient in the absence of channel error but its performance degrades rapidly over noisy channel. In this paper, in the case of appling bit selcetive error correction coding that protects some significant bits in a codeword, an efficient allocation method of imformation bits and additive redundancy bits used for quantization and error correction coding respectively under constant transmission bit rate is proposed, and its performance is analyzed. As a result, without increasing trasmission bit rate, PSNR can be improved up to 7~8 [dB] below bit error rate $10^2$ and the image without blocking effect caused by bit error resulted from channel noise can be recostructed.

• 한국통신학회논문지
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• 제37A권12호
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• pp.1043-1053
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• 2012

In distributed video coding (DVC) systems, the complexity of encoders is greatly reduced by removing the motion estimation operations in encoders, since the correlation between frames is utilized in decoders. The transmission of parity bits is requested through the feedback channel, until the related errors are corrected to decode the Wyner-Ziv frames. The requirement to use the feedback channel limits the application of DVC systems. In this paper, we propose an efficient method to remove the feedback channel in DVC systems. First, a simple side information generation method is proposed to calculate the amount of parity bits in the encoder, and it is shown that the proposed method yields good performance with low complexity. Then, by calibrating the theoretical entropy with three parameters, we can calculate the amount of parity bits in the encoder and remove the feedback channel. Moreover, an adaptive method to determine quantization parameters for key frames is proposed. Extensive computer simulations show that the proposed method yields better performance than conventional methods.

• 방송공학회논문지
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• 제14권2호
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• pp.144-153
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• 2009

최근, 사용자 제작 콘텐츠(UCC: User Created Contents) 또는 다시점 비디오(Multiview Video) 등의 응용을 위한 경량화 부호화 기술의 필요성이 대두됨에 따라 비디오 부호화 복잡도의 대부분을 차지하는 움직임 예측/보상 과정을 부호화기가 아닌 복호화기 측에서 수행하는 분산 비디오 부호화 기술(Distributed Video Coding)에 대한 연구가 활발히 이루어지고 있다. Wyner-Ziv 부호화 기술은 채널 코딩을 이용하여 원본 영상에 대한 복호화기 측의 예측영상인 보조정보에 포함된 잡음을 제거함으로써 영상을 복원하는 구조를 가진다. 일반적인 Wyner-Ziv 부호화 기술은 키 프레임 간의 움직임 예측/보상 과정에 기반한 프레임 보간법을 통해 보조정보를 생성하며, Shannon limit에 근접한 성능을 보이는 Turbo 코드나 LDPC 코드를 통해 잡음을 제거한다. Wyner-Ziv 부호화 기술은 채널 코드의 복호화를 위해 보조정보에 포함된 잡음의 정도를 예측하는데, 이를 '가상 채널 잡음(Virtual Channel Noise)'이라 하며 일반적으로 Laplacian이나 Gaussian으로 모델화 한다. 본 논문은 변환영역에서의 주파수 단위에 적응적인 채널 잡음 모델링에 기반한 Wyner-Ziv 부호화 방법을 제안한다. 다양한 영상에 대한 제안 방법의 실험 결과는 기존 방법과 비교하여 최대 약 0.52dB에 해당하는 율-왜곡 성능의 향상을 보여준다.

• ETRI Journal
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• 제27권5호
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• pp.635-638
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• 2005

Spatial audio coding (SAC) is an extremely high compact representation of encoded multi-channel audio material. This paper suggests a multi-channel audio service in the terrestrial digital multimedia broadcasting (T-DMB) system using a novel SAC tool, which is called a virtual source location information (VSLI)-based SAC tool. Intensive experiments are presented to evaluate the validity of the proposed VSLI-based SAC tool, and prototypical systems are also presented to demonstrate the reliability of the proposed multi-channel T-DMB system in real applications.

• 한국통신학회논문지
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• 제33권9A호
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• pp.867-873
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• 2008

Cyclic delay diversity (CDD) is considered as a simple approach to exploit the frequency diversity in OFDM system. In this paper, we apply CDD to the conventional STBC/SFBC/STFBC-OFDM transmit diversity schemes for Rayleigh fading channels. We compare the performances of STBC/SFBC/STFBC with and without CDD schemes. Simulation results show that the combination of block coding with CDD works well when using the ITU-R M. 1225 channel for both Pedestrian A (Ped A) channel with the mobility of 3 km/h, and Vehicular A (Veh A) channel with the mobility of 120km/h. For a BER of $10^{-3}$, compared to the conventional block coding schemes, a gain of 2dB, 4dB, and 5dB is obtained under the Ped A channel environment by STBC-OFDM, SFBC-OFDM and STFBC-OFDM with CDD, respectively Under the Veh A channel. gains by the combined schemes are 6dB, 2dB, and 4dB, respectivcly.

• 한국멀티미디어학회논문지
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• 제4권1호
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• pp.75-81
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• 2001

EBCOT(Embedded Block Coding with Optimized Truncation)는 현재 개발 중인 JPEG2000의 기본압축 코덱으로 본 논문에서는 EBCOT를 이용하여 하나의 압축 코덱에서 나온 이미지를 밴드 폭이 상이한 여러채널에 전송할 수 있는 방식에 대해 알아보고 이를 바탕으로 동영상에 적용하여 다채널 영상 전송 시스템을 제안한다. 또한 본 논문에서 사용되는 EBCOT가 JPEG에 쓰이는 RLC와 Huffman Coding 통한 VLC보다 압축 성능이 뛰어나다는 것을 실험적 결과를 통해 알 수 있고 JPEG에 적용할 경우 구조적으로 Paralleling의 증가와도 Error Resilience가 높다는 것을 알 수 있다. 다음으로 MPEG구조에 대해 알아보고 다 채널 영상 전송 시스템을 MPEG으로 구현 할 때의 Rate-Control이 힘든 문제와 원하는 Bit-Rate마다 코덱이 각각 있어야 하는 문제점 을 EBCOT를 적용시켜 해결할 수 있는 방법에 대해 제시한다.

• Journal of information and communication convergence engineering
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• 제8권6호
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• pp.655-659
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• 2010

In the conventional PNC scheme, the relay node requires simultaneous transmission of two source nodes with strict power control and carrier-phase matching between two received symbols. However, this pre-equalization process at source nodes is not practical in fading channels. In this letter, we propose a novel physical-layer network coding (PNC) scheme with log-likelihood ratio (LLR) conversion for fading channels, which utilizes not pre-equalizer at transmitters (source nodes) but joint detector at receiver (relay node). The proposed PNC requires only channel side information at the receiver (CSIR), which is far more practical assumption in fading channels. In addition, the proposed PNC scheme can use the conventional modulation scheme like M-QAM regardless of modulation order, while the conventional PNC scheme requires reconfiguration of modulation scheme at the source nodes for detection of the received signal at relay node. We consider the combination of the proposed PNC and channel coding, and find that the proposed PNC scheme is easily combined the linear channel codes such as turbo codes, LDPC, and convolutional codes.

• International Journal of Internet, Broadcasting and Communication
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• 제13권3호
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• pp.17-24
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• 2021

Recently, a lossless non-orthogonal multiple access (NOMA) implementation without successive interference cancellation (SIC) has been proposed in the literature of NOMA. This lossless non-SIC NOMA was achieved via correlated superposition coding (CSC), in contrast to conventional independent superposition coding (ISC). However, only the achievable data rates for CSC NOMA were investigated. Thus, this paper proposes a practical CSC NOMA scheme under Rayleigh fading channel environments. First, we design the practical CSC NOMA scheme, namely quadrature correlated superposition modulation (CSM) NOMA, without channel coding, i.e., uncoded systems. In addition, we calculate the symbol error rates (SERs) for this quadrature CSM NOMA scheme. Then, simulations demonstrate that for the weak channel gain's user, the SER performance of the proposed quadrature CSM NOMA is shown to be improved greatly, compared to that of the conventional quadrature amplitude modulation (QAM) NOMA, whereas for the strong channel gain's user, the SER performance of the proposed quadrature CSM NOMA degrades a little, compared to that of the conventional QAM NOMA. As a result, the proposed quadrature CSM NOMA scheme could be considered as a practical NOMA scheme for CSC NOMA schemes toward the fifth-generation (5G) and next generation communications.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2011년도 하계학술대회
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• pp.310-313
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• 2011

Broadcasting nature of wireless communications makes it possible to apply opportunistic network coding (OPNC) by overhearing transmitted packets from a source to sink nodes. However, it is difficult to apply network coding to the topology of multiple relay and sink nodes. We propose to use relay node selection, which finds a proper node for network coding since the OPNC alone in the topology of multiple relays and sink nodes cannot guarantee network coding gain. The proposed system is a novel combination of wireless network coding and relay selection, which is a key contribution of this paper. In this paper, with the consideration of channel state and potential network coding gain, we propose relay node selection techniques, and show performance gain over the conventional OPNC and a channel-based selection algorithm in terms of average system throughput.

• 디지털콘텐츠학회 논문지
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• 제5권2호
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• pp.121-127
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• 2004

본 논문은 주파수 선택성 라이시안 페이딩으로 모델링되는 다중경로 페이딩 환경에서 수신되는 직교주파수분할다증 (OFDM : Orthogonal Frequency Division Multiplexing 16 QAM (Quadrature Amplitude Modulation) 신호의 오율 성능을 해석하였다. 주파수 선택성 라이시안 페이딩으로는 라이시안의 심도 (K)를 이용하여 three-path 페이딩 모델을 사용하였으며, 성능 개선을 위하여 BCH 채널 부호화 기법을 채용하였다. 수치 해석에 의해, BCH채널 부호화에 의한 오율 성능의 개선 정도와 에러정정능력에 따른 개선 효과를 확인하였다. 결과적으로 채널 부호화 기법만으로는 무선 멀티미디어 통신에서 요구되는 오율 (10-6 정도)을 얻을 수 없으므로, 새로운 성능 개선 기법을 함께 채용하여야 하겠다.