• 대한전자공학회논문지TC
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• 제39권1호
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• pp.1-10
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• 2002

다중 사용자 DS-CDMA 시스템에서 더 좋은 성능을 얻고자 컨볼루션 부호와 시공간 차등 부호의 직렬 연쇄 구조를 제안한다. 본 논문에서 시스템은 다중 접속 간섭(MAI ; Multiple-access Interference) 를 억제하기 위해 다른 사용자의 확산 코드, 동기, 그리고 전력 정보 등을 필요로 하지 않는 단일 사용자 검파기(SUD : Single User Detection) 를 고려한다. 채널 부호로 사용된 부호화율 1 과 메모리 수 1 을 가지는 차등 부호는 부호화로 인한 효율 저하를 가져오지 않으며 최소 상태수를 가지게 된다. 그리고 시공간 블록 부호를 통해 다중 안테나로 인한 다이버시티 이득을 얻게 된다. 이러한 시공간 직렬 연쇄 컨볼루션 차등 부호를 복호함에 있어서 서로간의 정보를 교환하는 반복 복호 처리를 이용한다. 실험 결과로부터 본 시공간 연쇄 부호 기법이 DS-CDMA 시스템에서 기존의 컨볼루션 부호보다 유사한 복잡도에서 더 나은 성능과 유연성을 제공함을 알 수 있다. 또한 제안한 기법이 SUD를 하는 DS-CDMA 시스템에 적용될 때, 처리이득(PG : Processing Gain) 이나 간섭 억제 여파기의 탭 개수의 증가에 따라 성능 향상이 일어나며, 원근 간섭 전력 문제가 심한 경우에 성능 저하가 일어남을 알 수 있다.

• Journal of Communications and Networks
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• 제1권3호
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• pp.182-188
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• 1999

The optimal joint maximum-likelihood sequence estima-for using an array of antennas is derived for synchronous direct sequence-code division multiple access (DS-CDMA) system. Each user employs a rate 1/n convolutional code for channel coding for the additive white Gaussian noise (AWGN) channel. The array re-ceiver structure is composed of beamformers in the users' direc-tions followed by a bank of matched filters. The decoder is imple-mented using a Viterbi algorithm whose states depend on the num-ber of users and the constraint length of the convolutional code. The asymptotic array multiuser coding gain(AAMCG)is defined to encompass the asymptotic multiuser coding gain and the spatial information on users' locations in the system. We derive the upper and lower bounds of the AAMCG. As an example, the upper and lower bounds of AAMCG are obtained for the two user case where each user employes the maximum free distance convolutional code with rate 1/2. The enar-far resistance property is also investigated considering the number of antenna elements and user separations in the space.

• 한국통신학회논문지
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• 제25권3B호
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• pp.541-548
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• 2000

In the MPEG-4 standardization phase, many methods for coding the irregular shaped VOP (video object Plane) have been researched. Texture coding is one of interesting research items in the MPEG-4. There are the Low pass extrapolation (LPE) padding, the shape adaptive DCT (SA-DCT), and the Extension-Interpolation (EI)/2D-DCT proposed in [1] as texture coding methods. the EI/2D-DCT is the method extending and interpolating luminance values from and Arbitrarily Shaped (AS) image segment into an 8 x 8 block and transforming the extended and interpolated luminance values by the 8x8 DCT. although the EI/2D-DCT and the SA-DCT work well in coding the As image segments. they are degraded since they use one-dimensional (1-D) methods such as the 1D-EI and the 1D-DCT in the two-dimensional (2-D) space. in this paper, we analyze the performance of the EI/2D-DCTand propose a new non-symmetric sig-sag scanning method, which non-symmetrically scans the quantized coefficients in the DCT domain to improve the EI/2D-DCT.

• 한국통신학회논문지
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• 제34권1A호
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• pp.1-11
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• 2009

OFDMA 및 SC-FDMA 시스템에서, 수신기에서 특별한 시공간 처리를 하지 않으면서 다이버시티를 얻기 위해서, 다수 안테나를 이용하여 시간축의 변화를 일으키거나 주파수 선택적 채널을 만들 수 있다. 분산할당 SC-FDMA 시스템에서 시간 변화를 발생하기 위해 위상 회전 기술을 사용하기 위해서는 낮은 채널부호화율을 적용하는 것이 필요하지만, 시간 변화가 적은 채널을 가정할 때 주파수 선택적 특성을 증가시키기 위하여 순환지연 다이버시티를 적용할 때에는 상대적으로 높은 채널부호화율을 적용하여도 무방하다. 이에 반해서 블록호핑 SC-FDMA 시스템에서는 두 개의 다이버시티 기술이 최적의 채널부호화율 측면에서 큰 차이를 가지지 않는다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권3호
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• pp.956-970
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• 2015

In this paper, we study the design of network coding for the generalized transmit scheme in multiple input multiple output Y channel, where K users wish to exchange specified and shared information with each other within two slots. Signal space alignment at each user and the relay is carefully constructed to ensure that the signals from the same user pair are grouped together. The cross-pair interference can be canceled during both multiple accessing channel phase and broadcasting channel phase. The proposed signal processing scheme achieves the degrees of freedom of ${\eta}(K)=K^2$ with fewer user antennas.

• 한국통신학회논문지
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• 제40권9호
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• pp.1678-1685
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• 2015

본 논문에서는 신뢰도를 모르는 불완전한 채널 정보를 이용해 빔포밍 기법의 장점과 직교 시공간 블록 코딩 (Orthogonal Space-Time Block Coding, OSTBC) 기법의 장점을 결합해 주는 선형 프리코딩 기법을 제안한다. 먼저 다양한 값의 채널 정보의 신뢰도를 가정한 상태에서 각 신뢰도가 프리코딩 성능에 미치는 영향을 분석한다. 그 뒤, 효율적인 프리코더의 설계를 위하여 수신 SNR을 바탕으로 필요한 채널 정보의 신뢰도를 예측하는 방법을 제안한다. 시뮬레이션을 통해 제안된 프리코더 설계 기법의 효율성을 확인한다.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송∙미디어공학회 2019년도 추계학술대회
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• pp.259-260
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• 2019

MPEG-I Visual group is actively working on enhancing immersive experiences with up to six degree of freedom (6DoF). In virtual space of 3DoF+, which is defined as an extension of 360 video with limited changes of the view position in a sitting position, looking at the scene from another viewpoint (another position in space) requires rendering additional viewpoints using multiple videos taken at the different locations at the same time. In the MPEG-I Visual workgroup, methods of efficient coding and transmission of 3DoF+ video are being studied, and they released Test Model for Immersive Media (TMIV) recently. This paper presents the enhanced clustering method which can pack the patches into atlas efficiently in TMIV. The experimental results show that the proposed method achieves significant BD-rate reduction in terms of various end-to-end evaluation methods.

• 한국통신학회논문지
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• 제33권4A호
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• pp.426-433
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• 2008

In this paper, we present a method to improve the performance of the four transmit antenna quasi-orthogonal space-time block code (STBC) in the coded system. For the four transmit antenna case, the quasi-orthogonal STBC consists of two symbol groups which are orthogonal to each other, but intra group symbols are not. In uncoded system with the matched filter detection, constellation rotation can improve the performance. However, in coded systems, its gain is absorbed by the coding gain especially for lower rate code. We propose an iterative decoding method to improve the performance of quasi-orthogonal codes in coded systems. With conventional quasi-orthogonal STBC detection, the joint ML detection can be improved by iterative processing between the demapper and the decoder. Simulation results shows that the performance improvement is about 2dB at 1% frame error rate.

• 전기학회논문지P
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• 제63권1호
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• pp.29-33
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• 2014

This paper proposes an alternate time-switched space-frequency block coding transmission technique for single-carrier modulation with frequency domain equalization. There are two antennas in the transmitter but it still has only a baseband and RF and a switch that alternates between the antennas at every symbol timing. Alternating transmit symbols result in zeros which make maximal ratio receive combining possible in the receiver. Simulation results show that it has better performance than the traditional algorithm at the expense of one additional antenna.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2005년도 춘계학술발표대회
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• pp.1477-1480
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• 2005

AOC-SS (Advanced Orthogonal Code-Spread Spectrum) modulation [1] is a flexible scheme to obtain a multi-rate transmission but PAPR (Peak-to-Average Power Ratio) increases in proportion to the number of AOCs and thus, the mapping technique is proposed to solve this problem. Moreover, by combining with space-time coding (STC), AOC-SS is capable of resistance to multi-path fading. The simulation programs have been performed to verify the validity of the suggested scheme.