• 방송공학회논문지
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• 제24권4호
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• pp.613-622
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• 2019

코드북을 이용하는 폐루프 MISO 시스템에서 시간 상관성을 이용한 차분 코드북 설계 방법을 제안한다. 단일계층 코드북의 코드워드 인자들은 위상 성운의 집합 중에서 선택된다. 기존의 코드워드 선택 식에서는 코드워드들을 구면의 캡들이라 가정하고 서로의 각도를 사인 법칙을 이용하여 구하였으나, 본 논문에서는 피타고라스 법칙을 이용하는 새로운 방법을 이용하여 계산식을 간소화 시키는 식을 제안한다. 그리고 선택되는 코드워드간의 상관 계수 즉, 위상차의 변화를 추적하여 2 개의 코드북 중에 최적의 코드북을 적응적으로 선택하는 방법을 제안한다. Monte-Carlo 컴퓨터 시뮬레이션을 통해 제안하는 코드북의 성능을 검증한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권6호
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• pp.1828-1847
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• 2014

Coordinated multi-point (CoMP) transmission has been regarded as a potential technology for LTE-Advanced. In frequency division duplexing systems, channel quantization is applied for reporting channel state information (CSI). Considering the dynamic number of cooperation base stations (BSs), asymmetry feature of CoMP channels and high searching complexity, simply increasing the size of the codebook used in traditional multiple antenna systems to quantize the global CSI of CoMP systems directly is infeasible. Per-cell codebook based channel quantization to quantize local CSI for each BS separately is an effective method. In this paper, the theoretical upper bounds of system throughput are derived for two codeword selection schemes, independent codeword selection (ICS) and joint codeword selection (JCS), respectively. The feedback overhead and selection complexity of these two schemes are analyzed. In the simulation, the system throughput of ICS and JCS is compared. Both analysis and simulation results show that JCS has a better tradeoff between system throughput and feedback overhead. The ICS has obvious advantage in complexity, but it needs additional phase information (PI) feedback for obtaining the approximate system throughput with JCS. Under the same number of feedback bits constraint, allocating the number of bits for channel direction information (CDI) and PI quantization can increase the system throughput, but ICS is still inferior to JCS. Based on theoretical analysis and simulation results, some recommendations are given with regard to the application of each scheme respectively.

• 한국통신학회논문지
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• 제39A권3호
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• pp.155-157
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• 2014

In this paper, a novel codebook generation strategy is proposed. With the given codebooks, two codeword selection procedures are proposed and analyzed for generating the quantized multiple-input multiple-output (MIMO) channel state information (CSI). Furthermore, three different quantization and normalization strategies are analyzed. The simulation results suggest that the proposed 'quantized channel generation method 2' is the best strategy to reduce the quantization and normalization errors to generate the final quantized MIMO CSI.

• ETRI Journal
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• 제36권1호
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• pp.62-68
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• 2014

This paper presents a novel user selection method based on the signal-to-interference-plus-noise ratio (SINR), which is approximated using limited feedback data at the base stations (BSs) of multiple user multiple-input multiple-output (MU-MIMO) systems. In the proposed system, the codebook vector index, the quantization error obtained from the correlation between the measured channel and the codebook vector, and the measured value of the largest singular value are fed back from each user to the BS. The proposed method not only generates precoding vectors that are orthogonal to the precoding vectors of the previously selected users and are highly correlated with the codebook vector of each user but also adopts the quantization error in approximating the SINR, which eventually provides a significantly more accurate SINR than the conventional SINR-based user selection techniques. Computer simulations show that the proposed method enhances the sum rate of the conventional SINR-based methods by at least 2.4 (2.62) bps/Hz when the number of transmit antennas and number of receive antennas per user terminal is 4 and 1(2), respectively, with 100 candidate users and an SNR of 30 dB.

• 한국통신학회논문지
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• 제40권4호
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• pp.646-652
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• 2015

본 논문은 다중 사용자 MIMO 시스템에서 사용자 선택을 위해 필요한 precoding matrix index (PMI)/channel quality indication (CQI)의 보고 방식에 따른 성능을 분석한다. 이러한 분석을 통해 셀 내의 단말의 수, 선택되는 사용자의 수, 그리고 코드북(codebook)의 크기가 Best Companion Grouping (BCG)방식 스케쥴링의 성능에 복잡하게 영향을 미치는 것을 확인한다. 이에 따라 셀 내의 사용자 수와 코드북의 크기에 따라 동시에 스케쥴링 되는 사용자들의 그룹이 형성될 수 있는 확률이 달라지는 것을 확인할 수 있으며, 피드백 오버헤드가 주어졌을 때 이에 따라 피드백하는 PMI의 수와 사용하는 코드북의 크기를 적응적으로 선택함으로써 시스템의 평균 수율 성능을 최적화할 수 있음을 보였다.

• 대한음성학회:학술대회논문집
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• 대한음성학회 2006년도 춘계 학술대회 발표논문집
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• pp.37-40
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• 2006

In this paper, we propose a VQ codebook design of speech recognition feature parameters in order to improve the performance of a distributed speech recognition system. For the context-dependent HMMs, a VQ codebook should be correlated with phonetic distributions in the training data for HMMs. Thus, we focus on a selection method of training data based on phonetic distribution instead of using all the training data for an efficient VQ codebook design. From the speech recognition experiments using the Aurora 4 database, the distributed speech recognition system employing a VQ codebook designed by the proposed method reduced the word error rate (WER) by 10% when compared with that using a VQ codebook trained with the whole training data.

• 한국통신학회논문지
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• 제36권5C호
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• pp.276-285
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• 2011

본 논문에서는 한정된 자원에 여러 개의 연결이 혼재해 있는 상황에서 협력적으로 제한적인 피드백을 사용하여 성능을 개선시킬 수 있는 방법을 제안한다. 제안하는 방법은, 코드북에 있는 각 프리코더의 성능 우선순위에 따라 가중치를 부여하여 각 연결로부터 피드백 받은 가중치 데이터로부터 가중치의 합이 가장 높은 프리코더를 선택하는 방식이다. 시뮬레이션 결과 기존의 비협력적 방식에 비해 전송도 뿐만 아니라 시스템의 안정성에 관여되는 프리코더 선택의 수렴 정도 또한 향상됨을 알 수 있다.

• 전자공학회논문지B
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• 제31B권10호
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• pp.130-139
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• 1994

Video compression algorithms are based on removing spatial and/or temproal redundancy inherent in image sequences by predictive(DPCM) encoding, transform encoding, or a combination of predictive and transform encoding. In this paper, each 8$\times$8 DCT coefficient of DFD(displaced frame difference) is adaptively quantized by one of the four quantizers depending on total distortion level, which is determined by characteristics of HVS(human visual system) and buffer status. Therefore, the number of possible quantizer selection vectors(patterns) is 4$^{64}$. If this vectors are coded, toomany bits are required. Thus, the quantizer selection vectors are limited to 2048 for Y and 512 for each U, V by the proposed method using SWAD(sum of weighted absolute difference) for discriminating vectors. The computer simulation results, using the codebook vectors which are made by the proposed method, show that the subjective and objective image quality (PSNR) are goor with the limited bit allocation. (17Mbps)

• 대한전자공학회논문지TC
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• 제45권12호
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• pp.20-25
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• 2008

Codebook-based opportunistic beamforming (COBF) 기법은 파일럿을 적게 사용하면서 기존의 opportunistic beamforming 기법에 빔 선택 다이버시티를 추가한다. 본 논문에서는 채널의 상관도를 고려한 kappa-factor 채널 모델에 기반을 두어 COBF 기법에서 사용되는 랜덤 행렬과 코드북을 디자인한다. 디자인한 COBF를 적용하면 최적의 빔과 유사한 빔을 생성할 수 있고, 이에 따라 채널의 상관도가 높거나 낮음에 상관없이 항상 최적의 시스템 용량을 보인다.

• Journal of Communications and Networks
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• 제9권2호
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• pp.141-149
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• 2007

Multiple-input multiple-output (MIMO) transmit pre-coding/beamforming can significantly improve system spectral efficiency. However, several obstacles prevent precoding from wide deployment in early wireless networks: The significant feedback overhead, performance degradation due to feedback delay, and the large storage requirement at the mobile devices. In this paper, we propose a precoding method that addresses these issues. In this approach, only 3 or 6 bits feedback is needed to select a precoding matrix from a codebook. There are fifteen codebooks, each corresponding to a unique combination of antenna configuration (up to 4 antennas) and codebook size. Small codebooks are prestored and large codebooks are efficiently computed from the prestored codebook, modified Hochwald method and Householder reflection. Finally, the feedback delay is compensated by channel prediction. The scheme is validated by simulations and we have observed significant gains comparing to space-time coding and antenna selection. This solution was adopted as a part of the IEEE 802.16e specification in 2005.