• 한국통신학회논문지
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• 제29권4A호
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• pp.384-389
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• 2004

본 논문에서는 comb 방식의 파일럿 패턴을 가지는 MIMO OFDM 시스템에서의 채널 추정 기법에 대하여 논의한다. 또한, 시변 채널 환경에서 채널 측정의 정확도를 높이기 위한 효율적인 채널 추정 기법을 제안한다. 시뮬레이션을 통해 제안한 채널 추정 기법이 채널이 변하는 상황에서 성능의 감소 없이 채별의 변화를 추정함을 알 수 있었다.

• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1864-1876
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• 2015

In this paper, we propose a singular perturbation-like approach to EDFA gain controller design and analysis. Considering a three-level model of EDFA, a gain controller containing a state observer and a channel add/drop estimator is designed based on a singular perturbation - like concept. The proposed design methodology is shown to be effective and advantageous not only in theoretically verifying the asymptotic stability of systems with multi-time scales such as EDFA but also in designing an asymptotic estimator for channel add/drops which does not satisfy the matching condition.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.693-698
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• 2000

Aspects of classical information theory, such as rate distortion theory, investigate how to encode and decode information from an independently identically distributed source so that the asymptotic distortion rate between the source and its quantized representation is minimized. However, in most natural dynamics, the source state is highly corrupted by disturbances, and the measurement contains the noise. In recent coder-estimator sequence is developed for state estimation problem based on observations transmitted with finite communication capacity constraints. Unlike classical estimation problems where the observation is a continuous process corrupted by additive noises, the condition is that the observations must be coded and transmitted over a digital communication channel with finite capacity. However, coder-estimator sequence does not provide such a quantitative analysis as a variance for estimation error. In this paper, under the assumption that the estimation error is Gaussian distribution, a variance for coder-estimation sequence is proposed and its fitness is evaluated through simulations with a simple example.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.192-192
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• 2000

In this paper, a platoon merging is considered as a remote-controlled system with the state represented by a stochastic process. In this system, it becomes to encounter situations where a single decision maker controls a large number of subsystems, and observation and control signals are sent over a communication channel with finite capacity and significant transmission delays. Unlike classical estimation problem in which the observation is a continuous process corrupted by additive noise, there is a constraint that the observation must be coded and transmitted over a digital communication channel with finite capaci쇼. A recursive coder-estimator sequence is a state estimation scheme based on observations transmitted with finite communication capacity constraint. Using the coder-estimator sequence, the remote control station designs a feedback controller. In this paper, we introduce a stochastic model for the lead vehicle in a platoon of vehicles considering the angle between a road surface and a horizontal plane as a stochastic process. The simulation results show that the inter-vehicle distance and the deviation from the desired inter-vehicle distance are well regulated.

• 대한전자공학회논문지TC
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• 제46권2호
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• pp.46-52
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• 2009

본 논문에서는 직교 주파수 분할 다중 접속 방식(Orhogonal Frequency Division Multiple Access) 상향 링크 시스템에서 best linear unbiased estimator (BLUE)의 원리에 기반한 시간 동기 추정 알고리즘을 소개하며, 이 알고리즘을 기반으로 하여, 추정범위 제한 문제를 해결하기 위한 개선된 시간추정 기법을 추가적으로 제안한다. 새로운 추정 알고리즘은 인접한 부반송파 간의 차등 상관관계를 이용하여 주파수 축에서 시간 오차를 추정한다. 차등 상관관계는 시간 오차를 포함한 위상 정보를 나타내고, 채널의 주파수 선택적 특성에 의한 신호 왜곡을 완화시킨다. 기존의 추정 방법과 비교하여 제안된 추정 알고리즘은 비교적 정확한 추정 성능을 보인다. 실험 결과는 제안된 추정기가 상대적으로 작은 오차의 평균과 분산을 가지는 것을 확인하여 준다. 또한 실험은 신호 대 잡음비의 크기가 0에서 20 dB 사이일 때, 시간 추정 오차에 의한 제안된 추정기의 신호 대 잡음비 열화 정도가 0.4 dB 이하인 것을 보여준다. 따라서 제안된 동기 알고리즘은 OFDMA 상향 링크 시스템에서 다중 사용자의 시간동기추정에 적합하다.

• Journal of Communications and Networks
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• 제18권1호
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• pp.8-18
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• 2016

In this paper, we propose a number of blind equalization approaches for time-varying andmulti-path channels. The approaches employ cost reference particle filter (CRPF) as the symbol estimator, and additionally employ either least mean squares algorithm, recursive least squares algorithm, or $H{\infty}$ filter (HF) as a channel estimator such that they are jointly employed for the strategy of "Rao-Blackwellization," or equally called "mixture filtering." The novel feature of the proposed approaches is that the blind equalization is performed based on direct channel estimation with unknown noise statistics of the received signals and channel state system while the channel is not directly estimated in the conventional method, and the noise information if known in similar Kalman mixture filtering approach. Simulation results show that the proposed approaches estimate the transmitted symbols and time-varying channel very effectively, and outperform the previously proposed approach which requires the noise information in its application.

• 한국통신학회논문지
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• 제31권3A호
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• pp.282-290
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• 2006

본 논문에서는 2.45GHz 대역 IEEE 802.15.4 LR-WPAN(Low-Rate Wireless Personal Area Network; ZigBee) 시스템의 수신기를 위한 개선된 방식의 Timing estimator의 알고리즘을 제안한다. 저가 구현을 지향하는 LR-WPAN 시스템의 특성상 고가의 오실레이터를 사용할 수 없으므로 반송파 중심 주파수의 80ppm에 해당하는 주파수 옵셋 환경에서 안정된 동작이 가능한 Timing estimator 알고리즘이 요구된다. 본 논문에서는 이러한 수신 환경을 고려하여 Multiple delay differential filter를 적용함으로써 주파수 옵셋에 대한 강인성 및 수신 성능의 안정성을 증대시켰으며, Multiple delay differential filter의 출력 신호에 대한 reference 신호의 상관 결과가 I-channel 에만 국한되는 특성을 이용하여 일반적인 noncoherent 방식 대신 coherent 방식의 correlator를 적용함으로써 non-coherent 방식의 제곱 손실을 제거하여 검출 성능을 향상시킴과 동시에 복잡도를 감소시켜 초소형, 저전력, 저가를 지향하는 LR-WPAM 수신기에 보다 적합하도록 설계하였다. 다양한 채널 환경에서의 성능정가를 통하여 제안된 알고리즘이 differential detection 기반의 noncoherent 방식보다 평균적으로 2dB의 향상된 성능을 보임을 입증하였다.

• Journal of Communications and Networks
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• 제15권5호
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• pp.496-503
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• 2013

In an orthogonal frequency division multiplexing system, conventional interpolation techniques cannot correctly balance performance and overhead when estimating dynamic long-delay channels in single frequency networks (SFNs). In this study, classical filter analysis and design methods are employed to derive a complex interpolator for maximizing the resistible echo delay in a channel estimator on the basis of the correlation between frequency domain interpolating and time domain windowing. The coefficient computation of the complex interpolator requires a key parameter, i.e., channel length, which is obtained in the frequency domain with a tentative estimation scheme having low implementation complexity. The proposed complex adaptive interpolator is verified in a simulated digital video broadcasting for terrestrial/handheld receiver. The simulation results indicate that the designed channel estimator can not only handle SFN echoes with more than $200{\mu}s$ delay but also achieve a bit-error rate performance close to the optimum minimum mean square error method, which significantly outperforms conventional channel estimation methods, while preserving a low implementation cost in a short-delay channel.

• ETRI Journal
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• 제29권5호
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• pp.607-613
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• 2007

Most signal-to-noise ratio (SNR) estimation techniques in digital communication channels derive the SNR estimates solely from samples of the received signal after the matched filter. They are based on symbol SNR and assume perfect synchronization and intersymbol interference (ISI)-free symbols. In severe channel distortion where ISI is significant, the performance of these estimators badly deteriorates. We propose an SNR estimator which can operate on data samples collected at the front-end of a receiver or at the input to the decision device. This will relax the restrictions over channel distortions and help extend the application of SNR estimators beyond system monitoring. The proposed estimator uses the characteristics of the second order moments of the additive white Gaussian noise digital communication channel and a linear predictor based on the modified-covariance algorithm in estimating the SNR value. The performance of the proposed technique is investigated and compared with other in-service SNR estimators in digital communication channels. The simulated performance is also compared to the Cram$\acute{e}$r-Rao bound as derived at the input of the decision circuit.

• IEIE Transactions on Smart Processing and Computing
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• 제3권3호
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• pp.142-152
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• 2014

Vehicular Ad-hoc Networks (VANETs) are comprised of wireless mobile nodes characterized by a randomly changing topology, high mobility, availability of geographic position, and fewer power constraints. Orthogonal Frequency Division Multiplexing (OFDM) is a promising candidate for the physical layer of VANET because of the inherent characteristics of the spectral efficiency and robustness to channel impairments. The susceptibility of OFDM to Inter-Carrier Interference (ICI) is a challenging issue. The high mobility of nodes in VANET causes higher Doppler shifts, which results in ICI in the OFDM system. In this paper, a frequency domain com-btype channel estimation was used to cancel out ICI. The channel frequency response at the pilot tones was estimated using a Least Square (LS) estimator. An efficient interpolation technique is required to estimate the channel at the data tones with low interpolation error. This paper proposes a robust interpolation technique to estimate the channel frequency response at the data subcarriers. The channel induced noise tended to degrade the Bit Error Rate (BER) performance of the system. Parallel concatenated Convolutional codes were used for error correction. At the decoding end, different decoding algorithms were considered for the component decoders of the iterative Turbo decoder. A performance and complexity comparison among the various decoding algorithms was also carried out.