• 한국통신학회논문지
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• 제25권8B호
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• pp.1445-1452
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• 2000

일반적으로 통신채널은 심볼간 간섭(ISI)과 가산성 백색잡음(AWGN) 이 존재하는 환경으로 모델링할 수 있다 이러한 채널환경에서 비터비(Viterbi) 알고리즘은 송신측에서 전송한 데이터를 검출하기 위한 최적의 방법이다 하지만 비터비 알고리듬은 채널의 길이에 지수적으로 증가하는 많은 연산량 때문에 적합한 방법이 되지 못한다 이러한 문제점을 해결하기 위한방법들의 일종으로서 적응 등화기를 이용한 채널 등화 기법들이 널리 사용되고 있으나 채널이 혼합 위상 특성을 가지는 경우에는 비효율적인 방법이다 본 논문에서는 혼합 위상 특성을 가지는 채널을 위한 효율적인 채널 등화기를 제안하였으며 기존의 채널 등화 기법들과 비교하여 제안한 방법의 우수성을 보였다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2002년도 하계종합학술대회 논문집(1)
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• pp.323-326
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• 2002

In this paper, we study the improved bounds on the performance of low-density parity-check (LDPC) codes over binary-input additive white Gaussian noise (AWGN) channels with belief propagation (BP) decoding in log domain. We define an extended Gallager ensemble based on a new method of constructing parity check matrix and make use of this way to improve upper bound of LDPC codes. At the same time, many simulation results are presented in this paper. These results indicate the extended Gallager ensembles based on Hamming codes have typical minimum distance ratio, which is very close to the asymptotic Gilbert Varshamov bound and the superior performance which is better than the original Gallager ensembles.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 1998년도 추계학술대회 학술발표 논문집
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• pp.474-478
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• 1998

A new approach for the decision feedback equalizer(DFE) based on the back-propagation neural networks is described. We propose the method of optimal structure for back-propagation neural networks model. In order to construct an the optimal structure, we first prescribe the bounds of learning procedure, and the, we employ the method of incrementing the number of input neuron by utilizing the derivative of the error with respect to an hidden neuron weights. The structure is applied to the problem of adaptive equalization in the presence of inter symbol interference(ISI), additive white Gaussian noise. From the simulation results, it is observed that the performance of the propose neural networks based decision feedback equalizer outperforms the other two in terms of bit-error rate(BER) and attainable MSE level over a signal ratio and channel nonlinearities.

• 한국통신학회논문지
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• 제14권3호
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• pp.240-248
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• 1989

본 논문에서는 MSK보다 훨씬 효율적인 주파수 대역 특성을 갖는 QORC 변조 방식의 성능을 가진 백색 가우시안 잡음 하에서 분석하였다. 수신기는 QPSK 방식에서 사용되는 동기(Coherent) 수신기를 사용하고 신호 검출을 위한 샘플링 시간은 QORC 신호를 고려하여 [(2n-1)T, (2n+1)T]로 하였다. 분석 결과 QORC는 대역폭이 MSK에 비하여 1/16정도로 압축되며 성능면에서는 낮은 오류 발생 확률에서 약 1dB 정도의 전력을 더 필요로 하여 거의 동등하였다.

• 한국통신학회논문지
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• 제26권11A호
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• pp.1803-1811
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• 2001

본 논문에서는 미국의 유선 케이블 모뎀 규격인 MCNS(Multimedia Cable Network System) DOCSIS(Data Over Cable Service Interface Specification)를 만즉하는 하향 채널의 64/256-QAM 수신부 FEC(Forward Error Correction)를 분석하였다. FEC는 기본적으로 RS(Reed-Solomon) 계층과 TCM(Trellis Coded Modulation) 계층으로 구분되며, 여기에 추가적으로 interleaving과 randomizer 계층들이 결합되어 있다. AWGN(Additive White Gaussian Noise) 환경에서의 BER(Bit Error Rate) 성능평가를 통해 수신부 연판정 비터비 복호기(soft Viterbi decoder)의 추적 깊이(trace-back depth)와 양자화 레벨(quantization level)의 크기에 따라 부호화 이득이 변함을 확인하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2011년도 추계학술대회
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• pp.882-885
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• 2011

This paper presents testing and self-calibration of RF circuits using MEMS switches to identify process-related defects and out of specification circuits. We have developed a novel multi-tone dither test technique where the test stimulus is generated by modulating the RF carrier signal with a multi-tone signal generated using an Arbitrary Waveform Generator (AWG) with additive white Gaussian noise. This test stimulus is provided as input to the RF circuit and peak-to-average ratio (PAR) is measured at the output. For a faulty circuit, a significant difference is observed in the value of PAR as compared to a fault-free circuit. Simulation is performed for various circuit conditions such as fault-free as well as fault-induced and their corresponding PARs are stored in the look-up table. This testing and self-calibration technique is exhaustive and efficient for present-day communication systems.

• 한국정보통신학회논문지
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• 제5권4호
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• pp.639-644
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• 2001

직접 확산 부호 분할 다원 접속시스템과 시분할 다원 접속시스템을 동일 주파수 대역에서 중첩되어 전송할 때 DS-CDMA 신호에서의 TDMA 신호의 협대역 간섭이 문제된다. 본 논문에서는 DS-CDMA 신호의 협대역 간섭파를 제거하는 방법으로서 복소 다중 비율 필터 뱅크(Complex Multirate Filter Bank : CMFB)를 이용해서 협대역 간섭파 제거법을 제안하고, 간섭제거기(CCI canceller)를 이용해서 다중접속 간섭을 제거하여 DS-CDMA 신호의 성능을 개선한다. 본 논문은 AWGN, MAI 및 NI환경하에서 DS-CDMA 신호와 TDMA 신호의 주파수 공용 시스템에 적용할 때의 DS-CDMA신호의 특성에 대해서 해석하였다. 또 한, 복소 필터 뱅크와 간섭제거기를 직렬 연결한 노치필터를 채용하여 성능개선을 이룰 수 있었다.

• Journal of Information Processing Systems
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• 제15권2호
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• pp.271-287
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• 2019

The synchronization scheme based on moving average is robust and suitable for the same rule to be adopted in embedding watermark and synchronization code, but the imperceptibility and search efficiency is seldom reported. The study aims to improve the original scheme for robust audio watermarking. Firstly, the survival of the algorithm from desynchronization attacks is improved. Secondly, the scheme is improved in inaudibility. Objective difference grade (ODG) of the marked audio is significantly changed. Thirdly, the imperceptibility of the scheme is analyzed and the derived result is close to experimental result. Fourthly, the selection of parameters is optimized based on experimental data. Fifthly, the search efficiency of the scheme is compared with those of other synchronization code schemes. The experimental results show that the proposed watermarking scheme allows the high audio quality and is robust to common attacks such as additive white Gaussian noise, requantization, resampling, low-pass filtering, random cropping, MP3 compression, jitter attack, and time scale modification. Moreover, the algorithm has the high search efficiency and low false alarm rate.

• ETRI Journal
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• 제43권2호
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• pp.197-208
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• 2021

Single-carrier frequency division multiple access (SC-FDMA) is currently being used in long-term evolution uplink communications owing to its low peak-to-average power ratio (PAPR). This study proposes a new transceiver design for an SC-FDMA system based on Walsh-Hadamard transform (WHT). The proposed WHT-based SC-FDMA system has low-PAPR and better bit-error rate (BER) performance compared with the conventional SC-FDMA system. The WHT-based SC-FDMA transmitter has the same complexity as that of discrete Fourier transform (DFT)-based transmitter, while the receiver's complexity is higher than that of the DFT-based receiver. The exponential companding technique is used to reduce its PAPR without degrading its BER. Moreover, the performances of different ordered WHT systems have been studied in additive white Gaussian noise and multipath fading environments. The proposed system has been verified experimentally by considering a real-time channel with the help of wireless open-access research platform hardware. The supremacy of the proposed transceiver is demonstrated based on simulated and experimental results.

• ETRI Journal
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• 제45권2호
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• pp.226-239
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• 2023

Challenges in cognitive radio and tactical communications include recognizing anonymously received signals and estimating parameters in a blind or semi-blind manner. In this paper, we examine this issue for orthogonal frequency division multiplexing (OFDM) signaling. There are several parameters in OFDM signaling, and the blind receiver must extract and consider the synchronization issue. We assume that the blind receiver is aware of modulation type, OFDM, and not aware of chip duration and the length of cyclic prefix. First, we present new criteria based on kurtosis to estimate these parameters and compare their performance at different levels of additive white Gaussian noise with methods based on correlation, kurtosis, maximum likelihood, and matched filter. Then, we perform synchronization and estimate the start time based on these criteria and several new criteria in two steps: fine and coarse synchronization. Finally, in a more practical setup, we present the idea of jointly estimating the mentioned parameters and the signal start time as coarse synchronization. We compare different criteria and show that one of the proposed criteria has the highest efficiency.