• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권12호
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• pp.5129-5148
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• 2016

In this paper, the average bit error probability (ABEP) performance of the incremental-selective decode-and-forward (ISDF) relaying mobile-to-mobile (M2M) cooperative networks over N-Nakagami fading channels is investigated. The exact ABEP expressions are derived, and the power allocation problem is formulated.The derived ABEP expressions are verified by Monte Carlo simulations. The simulation results showed that the propagation parameters, such as the fading coefficient, and the power-allocation parameter, have a significant influence on the ABEP performance.

• 정보보호학회논문지
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• 제6권3호
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• pp.71-86
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• 1996

본 논문에서는 ATM(Asynchronous Transfer Mode) 망의 ABR(Available Bit-Rate) 서비스를 위한 폭주 제어 기법 내에서 사용되는 스위치 알고리즘을 제안한다. 이 알고리즘은 명시적 전송률 할당 알고리즘으로서 셀의 전송 경로 중 피드백 지연 시간을 가상적으로 단축하여 왕복 지연이 큰 망 환경과 효율성을 유지한다는 것을 시뮬레이션을 통하여 보인다.

• International Journal of Advanced Culture Technology
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• 제9권4호
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• pp.307-314
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• 2021

Recently, positively asymmetric binary pulse amplitude modulation (2PAM) has been proposed to improve the bit error rate (BER) performance of the weak channel gain user, with a tolerable BER loss of the strong channel gain user, for non-orthogonal multiple access (NOMA). However, the BER loss of the stronger channel gain user is inevitable in such positively asymmetric 2PAM NOMA scheme. Thus, we propose the negatively asymmetric 2PAM NOMA scheme. First, we derive closed-form expressions for the BERs of the negatively asymmetric 2PAM NOMA. Then, simulations demonstrate that for the stronger channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA improves, compared to that of the conventional positively asymmetric 2PAM NOMA. Moreover, we also show that for the weaker channel gain user, the BER of the proposed negatively asymmetric 2PAM NOMA is comparable to that of the conventional positively asymmetric 2PAM NOMA, over the power allocation range less than about 10 %.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권9호
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• pp.3823-3840
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• 2020

Recently, auto-encoder has emerged as the most popular method in convolutional neural network (CNN) based image compression and has achieved impressive performance. In the traditional auto-encoder based image compression model, the encoder simply sends the features of last layer to the decoder, which cannot allocate bits over different spatial regions in an efficient way. Besides, these methods do not fully exploit the contextual information under different receptive fields for better reconstruction performance. In this paper, to solve these issues, a novel auto-encoder model is designed for image compression, which can effectively transmit the hierarchical features of the encoder to the decoder. Specifically, we first propose an adaptive bit-allocation strategy, which can adaptively select an importance channel. Then, we conduct the multiply operation on the generated importance mask and the features of the last layer in our proposed encoder to achieve efficient bit allocation. Moreover, we present an additional novel perceptual loss function for more accurate image details. Extensive experiments demonstrated that the proposed model can achieve significant superiority compared with JPEG and JPEG2000 both in both subjective and objective quality. Besides, our model shows better performance than the state-of-the-art convolutional neural network (CNN)-based image compression methods in terms of PSNR.

• 한국통신학회논문지
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• 제23권6호
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• pp.1461-1470
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• 1998

비트 할당 문제는 허용 비트량을 초과하지 않는 상황에서 복호된 영상의 왜곡을 최소화하는 방법을 찾는 것으로 영상 손실 부호화에 있어서 가장 기본적으로 요구되는 점이라 할 수 있다. 이 문제의 최적 해는 Lagrangian 방식을 이용하여 계산량을 줄이면서도 최적해에 근접하는 복원 영상을 얻을 수 있는 비트 할당 기법을 제안한다. 이를 위하여 기존의 활성도 측정 방식들을 비교 검토하였으며, 활성도 값과 할당 비트량과의 관계를 파악하였다. MPEG-1 Intra 부호화 방법에 제안 기법을 적용하여 실험 영상을 부호화 하는 경우, 적은 계산량만으로도 최적 해에 근접하는 결과를 얻을 수 있었다.

• 한국전자통신학회논문지
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• 제15권6호
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• pp.1131-1136
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• 2020

협력 네트워크는 중계기를 이용하여 신호를 전송하고, 수신기에서는 여러 중계기를 통해서 수신된 신호를 결합하여 복조함으로써 통신성능을 향상시킬 수 있다. 본 논문에서는 송신기-중계기 사이에서는 일반적인 변조 방식을 사용하고 중계기-수신기 사이에서는 공간 시간 코드 방식을 적용하는 협력 네트워크 시스템을 가정하여, 자원 할당에 따른 효과를 분석한다. 일반적인 변조 방식은 동기 변조 방식과 차등 변조 방식 두 가지를 고려하고 공간 시간 코드 방식은 차등 변조 방식을 적용한다. 자원 할당은 중계기의 위치와 전송에너지를 고려하며 중계기의 개수에 따른 성능 또한 분석한다.

• 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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• 제25권5A호
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• pp.726-742
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• 2000

A novel rte control algorithm consisting of two major components, i.e. a variable encoding frame rate method and a hybrid DCT/wavelet I-frame coding scheme, is proposed in this work for low bit rate video coding. Most existing rate control algorithms for low bit rate video focus on bit allocation at the macroblock level under a constant frame rate assumption. The proposed rate control algorithm is able to adjust the encoding frame rate at the expense of tolerable time-delay. Furthermore, an R-D optimized hybrid DCT/wavelet scheme is used for effective I-frame coding. The new rate-control algorithm attempts to achieve a good balance between spatial quality and temporal quality to enhance the overall human perceptual quality at low bit rates. It is demonstrated that the rate control algorithm achieves higher coding efficiency at low bit rates with a low additional computational cost. The variable frame rate method and hybrid I-frame coding scheme are compatible with the bi stream structure of H.263+.

• International Journal of Internet, Broadcasting and Communication
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• 제12권4호
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• pp.18-25
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• 2020

In the fifth generation (5G) and beyond 5G (B5G) mobile communication, non-orthogonal multiple access (NOMA) has attracted great attention due to higher spectral efficiency and massive connectivity. We investigate the impacts of the channel estimation errors on the bit-error rate (BER) of NOMA, especially with the single-user decoding (SUD) receiver, which does not perform successive interference cancellation (SIC), in contrast to the conventional SIC NOMA scheme. First, an analytical expression of the BER for SUD NOMA with channel estimation errors is derived. Then, it is demonstrated that the BER performance degrades severely up to the power allocation less than about 20%. Additionally, we show that for the fixed power allocation of 10% in such power allocation range, the signal-to-noise (SNR) loss owing to channel estimation errors is about 5 dB. As a consequence, the channel estimation error should be considered for the design of the SUD NOMA scheme.

• ETRI Journal
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• 제36권3호
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• pp.506-509
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• 2014

This paper studies the energy efficiency power allocation for cognitive radio networks based on uplink orthogonal frequency-division multiplexing. The power allocation problem is intended to minimize the maximum energy efficiency measured by "Joule per bit" metric, under total power constraint and robust aggregate mutual interference power constraint. However, the above problem is non-convex. To make it solvable, an equivalent convex optimization problem is derived that can be solved by general fractional programming. Then, a robust energy efficiency power allocation scheme is presented. Simulation results corroborate the effectiveness of the proposed methods.