• Journal of Korea Society of Industrial Information Systems
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• 제25권5호
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• pp.13-21
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• 2020

This paper proposes a sign reversal channel switching method in space-frequency block code for orthogonal frequency division multiplexing system. In case of sending source data on other antenna, it is necessary for the receiver to change combining method according to the channel variation. If one does not know the predefined channel switching sequence, it is not possible to decode the received data precisely. In transmit data symbols' exchanges for a channel switching, data symbols are exchanged according to a format of space-frequency block code. In this paper, we proposes a simple sign reversal method except exchanging data symbols between transmit antennas. It is shown that this method occurs another combining method for a simple encryption in the receiver.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제34권9C호
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• pp.915-921
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• 2009

Lenstra-Lenstra-Lovasz (LLL) algorithm, which is one of the lattice reduction (LR) techniques, has been extensively used to obtain better bases of the channel matrix. In this paper, we jointly apply Seysen's lattice reduction Algorithm (SA), instead of LLL, with the conventional linear precoding algorithms. Since SA obtains more orthogonal lattice bases compared to those obtained by LLL, lattice reduction aided (LRA) precoding based on SA algorithm outperforms the LRA precoding with LLL. Simulation results demonstrate that a gain of 0.5dB at target BER of $10^{-5}$ is achieved when SA is used instead of LLL or the LR stage.

• The Journal of Korean Institute of Information Technology
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• 제17권10호
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• pp.49-55
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• 2019

In this paper, we propose a simple precoding vector design scheme for multi-user multiple-input single-output (MISO) interference channel when there are multiple eavesdroppers. We aim to obtain a mathematical closed-form solution of the secrecy rate optimization problem. For this goal, we design the precoding vector based on the signal-to-leakage plus noise ratio (SLNR). More specifically, the proposed precoding vector is designed to completely eliminate a wiretap channel capacity for refraining the eavesdroppers from detecting the transmitted information, and to maximize the transmitter-receiver link achievable rate. We performed simulation for the performance investigation. Simulation results show that the proposed scheme has better secrecy rate than the conventional scheme over all signal-to-noise ratio (SNR) range even though the special condition among the numbers of transmit antennas, transmitter-receiver links, and eavesdroppers is not satisfied.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 한국방송∙미디어공학회 2020년도 추계학술대회
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• pp.169-171
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• 2020

CNN의 중간 단계에서 추출되는 feature를 인코딩했을 때 결과 성능평가에 미치는 영향을 알아보는 실험을 수행하였다. 물체검출(Object detection)과 물체영역분할(Object segmentation)에 대하여 성능평가를 하였으며, 비교를 위해 원본 이미지와 256채널의 feature들을 한 장으로 합친 이미지 두 가지에 대해 인코딩하여 성능 평가를 실시하는 실험을 하여 결과를 도출했다. 실험 결과, 인코딩 시 압축 정도를 약하게 했을 경우 성능이 거의 떨어지지 않거나 심지어는 더 높은 경우도 있다. 하지만 256채널의 feature들에 대하여 인코딩을 하기 때문에 이미지의 용량과 해상도가 높아지는 단점이 있다.

• Proceedings of the KIEE Conference
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• 대한전기학회 2008년도 학술대회 논문집 정보 및 제어부문
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• pp.286-287
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• 2008

본 논문은 멀티채널 오디오 신호를 두 채널의 다운믹스신호와 서브밴드별로 추출된 부가 정보로 표현하는 파라메트릭 멀티채널 압축 방식에 관한 연구이다. 기존의 파라메트릭 멀티채널 방식에서 사용하는 부가 정보로는 ICLD, ICC, OPD, IPD 등이 있다. 본 논문에서는 부가 정보로서 phase관련 파라미터를 사용하지 않고, 채널간의 level difference에 상응하는 파라미터와 새로 제안한 diffuseness 계수를 사용하여 우수한 압축 성능을 보이는 파라메트릭 멀티채널 코딩 방식을 제안하고, 그 성능을 기존 방법과 비교하고자한다.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• 제12권3호
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• pp.87-95
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• 2013

In this paper, the outage probability of efficient partial relay selection(EPRS) using only one-hop channel information in multi-hop systems is analyzed in Rayleigh fading channels. In particular, we derive an exact and closed-form expression for the outage probability of decode-and-forward relaying based EPRS. In order to prove the usefulness of EPRS in multi-hop systems, we also analyze the correlation between the end-to-end signal-to-noise ratio(SNR) and the SNR for each hop at an arbitrary relaying path. Furthermore, through numerical investigation, we compare the outage performances for EPRS and the best relay selection using all channel information.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제28권1C호
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• pp.81-89
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• 2003

For improving the performance of noise suppression in tactical communication environments, an enhanced MELP vocoder is suggested, in which an acoustic noise suppressor is integrated into the front end of the MELP algorithm, and an FEC code into the channel side of the MELP algorithm. The acoustic noise suppressor is the modified IS-127 EVRC noise suppressor which is adapted for the MELP vocoder. As for FEC, the turbo code, which consists of rate-113 encoding and BCJR-MAP decoding algorithm, is utilized. In acoustic noise environments, the lower the SNR becomes, the more the effects of noise suppression is increased. Moreover, The suggested system has greater noise suppression effects in stationary noise than in non-stationary noise, and shows its superiority by 0.24 in MOS test to the original MELP vocoder. When the interleave size is one MELP frame, BER 10-6 is accomplished at channel bit SNR 4.2 ㏈. The iteration of decoding at 3 times is suboptimal in its complexity vs. performance. Synthetic quality is realized as more than MOS 2.5 at channel bit SNR 2 ㏈ in subjective voice quality test, when the interleave size is one MELP frame and the iteration of decoding is more than 3 times.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제37권6A호
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• pp.450-457
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• 2012

For orthogonal frequency-division multiplexing (OFDM) systems, we propose a blind channel estimation scheme based on non-redundant precoding. In the proposed scheme, a modified covariance matrix is first obtained by dividing the covariance matrix of the received signal vector by the precoding matrix element-by-element. Then, the channel vector is estimated as an eigenvector corresponding to the largest eigenvalue of the modified covariance matrix. The eigenvector can be obtained by power method with low computational complexity instead of the complicated eigenvalue decomposition. We analytically derive a mean square error (MSE) of the proposed channel estimation scheme and show that the analysis result coincides well with the simulation result. Also, simulation results show that the proposed scheme has better MSE and bit error rate (BER) performance than conventional channel estimation schemes.

• Proceedings of the Korea Information Processing Society Conference
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• 한국정보처리학회 2002년도 춘계학술발표논문집 (하)
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• pp.1615-1618
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• 2002

본 논문은 MAP(Maximum A Posteriori) 복호 알고리즘을 이용한 MAP Decoder의 설계에 관해 다룬다. 채널코딩기법은 채널을 통해서 디지털 정보를 전송할 때 신뢰성을 제공하기 위해서 사용되어 진다. 즉 수신단에서 수신된 정보의 오류를 검사하고 수정하기 위한 목적으로 송신단에서는 디지털 정보에 부가 정보를 첨가해서 전송하게 된다. 그래서 무선 이동 통신에서 성능이 우수한 채널코딩기법은 우수한 통신 품질을 위해서는 필수적이라고 할 수 있다. 최근에 Shannon의 한계에 매우 근접한 성능으로 많이 알려진 오류정정부호로 터보코드가 발표되었고 많은 연구가 진행되고 있다. 터보코드의 부호기로는 RSC(recursive systematic convolutional)코드가 사용되며 디코딩 알고리즘으로는 주로 MAP 복호 알고리즘을 사용한다. 본 논문에서 제안된 MAP 복호기는 하드웨어로 구현하기 위해서 변형된 LOG-MAP 복호 알고리즘을 이용하였고 터보디코더의 반복 복호에 이용할 수 있다.

• The Journal of the Korea Contents Association
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• 제10권9호
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• pp.88-96
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• 2010

We propose the efficient channel coding method combined with a 2.4kbps speech coder. The code rate of a channel coder is given by 1/2 and 1/2 rate convolutional coder is obtained from the punctured convolutional coder with rate of 1/3. The punctured convolutional coder is used for a variable rate allocation. The puncturing method according to the importance of the output data of the source encoder is applied for the convolutional coder. The importance of output data is analyzed by evaluating the bit error sensitivity of speech parameter bits. The performance of proposed coder is analyzed and simulated in Rayleigh fading channel and AWGN channel. The experimental results with 2.4kbps EHSX coder show that the variable rate channel coding method is superior to non-variable channel coding method from the subjective speech quality.