• 한국정보통신학회논문지
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• 제13권12호
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• pp.2731-2736
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• 2009

본 논문에서는 직교 기저행렬을 이용한 직교 주파수분할다중화 시스템의 새로운 구현방안이 수학적으로 개발된다. 직교기저행렬은 Haar 기저행렬을 기본으로 하고 있으나 직교 주파수분할다중화의 다중 부채널 신호를 변조하기에 적당한 형태를 갖추고 있다. 여기서는 새로운 기저행렬이 간단한 재귀알고리즘에 의하여 확장될 수 있음이 증명된다.그리고 송신기 조합행렬의 차수는 확장에 의하여 두배로 증가된다. 수신기에서 복조는 직교 기저행렬의 재귀에 의하여 생성되는 조합행렬의 역행렬에 의하여 수행된다. 따라서 제안된 직교 주파수분할다중화 시스템에서는 원 신호의 완벽한 재생이 가능함을 알 수 있다.

• 전자공학회논문지B
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• 제31B권7호
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• pp.91-100
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• 1994

The lapped orthogonal transform(LOT) has been recently proposed to alleviate the blocking effects in transform coding. The LOT is known to provide an improved coding gain than the conventional transform. In this paper, we propose a prefilter approach to design the LOT bases with the view of maximizing the transform coding gain. Since the nonlinear phase basis is inappropriate to the image coding only the linear phase basis is considered in this paper. Our approach is mainly based on decomposing the transform matrix into the orthogonal matrix and the prefilter matrix. And by assuming that the input is the 1st order Markov source we design the prefilter matrix and the orthogonal matirx maximizing the transform coding gain. The computer simulation results show that the proposed LOT provides about 0.6~0.8 dB PSNR gain over the DCT and about 0.2~0.3 dB PSNR gain over the conventional LOT [7]. Also, the subjective test reveals that the proposed LOT shows less blocking effect than the DCT.

• Journal of Communications and Networks
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• 제5권4호
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• pp.328-343
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• 2003

Orthogonal pulse-shape modulation using Hermite pulses for ultra-wideband communications is reviewed. Closedform expressions of cross-correlations among Hermite pulses and their corresponding transmit and receive waveforms are provided. These show that the pulses lose orthogonality at the receiver in the presence of differentiating antennas. Using these expressions, an algebraic model is established based on the projections of distorted receive waveforms onto the orthonormal basis given by the set of normalized orthogonal Hermite pulses. Using this new matrix model, a number of pulse-shape modulation schemes are analyzed and a novel orthogonal design is proposed. In the proposed orthogonal design, transmit waveforms are constructed as combinations of elementary Hermites with weighting coefficients derived by employing the Gram-Schmidt (QR) factorization of the differentiating distortion model’s matrix. The design ensures orthogonality of the vectors at the output of the receiver bank of correlators, without requiring compensation for the distortion introduced by the antennas. In addition, a new set of elementary Hermite Pulses is proposed which further enhances the performance of the new design while enabling a simplified hardware implementation.

• Journal of information and communication convergence engineering
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• 제5권1호
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• pp.12-16
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• 2007

In this paper, a new method is proposed for tracking the direction-of-arrival (DOA) of the wideband moving source incident on uniform linear array sensors. DOA is estimated by focusing transformation matrices. To update focusing matrices along with new data snap shots, we use the FAST (Fast Approximate Subspace Tracking) method. Present focusing matrices are constructed by previous signal and its orthogonal basis vectors as well as present signal and its orthogonal basis vectors, which are the left and right singular vectors of the inner product of two approximated matrices. Simulation results are shown to illustrate the performance of the proposed method.

• Current Optics and Photonics
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• 제5권6호
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• pp.686-698
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• 2021

A camouflaged encryption scheme based on Hadamard matrix and ghost imaging is proposed. In the process of the encryption, an orthogonal matrix is used as the projection pattern of ghost imaging to improve the definition of the reconstructed images. The ciphertext of the secret image is constrained to the camouflaged image. The key of the camouflaged image is obtained by the method of sparse decomposition by principal component orthogonal basis and the constrained ciphertext. The information of the secret image is hidden into the information of the camouflaged image which can improve the security of the system. In the decryption process, the authorized user needs to extract the key of the secret image according to the obtained random sequences. The real encrypted information can be obtained. Otherwise, the obtained image is the camouflaged image. In order to verify the feasibility, security and robustness of the encryption system, binary images and gray-scale images are selected for simulation and experiment. The results show that the proposed encryption system simplifies the calculation process, and also improves the definition of the reconstructed images and the security of the encryption system.

• 전자공학회논문지
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• 제51권9호
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• pp.30-40
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• 2014

본 논문에서는 Hadamard 변환이 Jacket 변환으로 일반화 될 수 있는 것처럼 Haar 변환을 Jacket-Haar 변환으로 일반화 한다. Jacket-Haar 변환의 원소는 0 과 ${\pm}2^k$ 이다. original Haar 변환과 비교해서 Jacket-Haar 변환의 베이시스(basis)는 신호처리에 보다 적합하다. 응용으로 $2{\times}2$ Hadamard 행렬을 기반으로 한 DCT-II(discrete cosine transform-II)와 $2{\times}2$ Haar 행렬을 기반으로 한 HWT(Haar Wavelete transform)를 제시하고 이들의 성능을 분석하며 Lenna 이미지의 시뮬레이션을 통해 성능을 평가하였다.

• Journal of electromagnetic engineering and science
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• 제7권4호
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• pp.195-200
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• 2007

Doubly-selective channel estimator for orthogonal frequency division multiplexing(OFDM) systems is proposed in this paper. Based on the generalized complex exponential basis expansion model(GCE-BEM), we describe the time-variant channel with time-invariant coefficients over multiple OFDM blocks. The time variation of the channel destroys the orthogonality between subcarriers, and the resulting channel matrix in the frequency domain is no longer diagonal, but the main interference comes from the near subcarriers. Based on this, we propose a channel estimator with low pilot ratio. We first develop a least-square(LS) estimator under the assumption that only the maximum Doppler frequency and the channel order are known at the receiver, and then verify that the correlation matrix of inter-channel interference(ICI) is a scaled identity matrix based on which we derive an optimal pilot insertion scheme for the LS estimator in the sense of minimum mean square error. The proposed estimator has the advantages of low pilot ratio and robustness against inter-carrier interference.

• 한국통신학회논문지
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• 제22권12호
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• pp.2706-2713
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• 1997

The fast implementation algorithm of M-band discrete wavelet transform is propsed using the factorization of lossless matrix when the length of discrete orthogonal wavelet bases equals to 2M. In computational complexity when direct filtering method is employed, the number of multiplicationand addition is (2M$^{2}$) and (2M$^{2}$ -M), respectively. But by proposed algorithm, it can be reduced to (M$^{2}$+M) and (M$^{2}$+2M-1), respectively. and it is possible to reduce the compuatational complexity further when unitary matrix employed to design the discrete or thogonal wavelet basis has the fast algorithm.

• 한국음향학회지
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• 제38권5호
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• pp.534-542
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• 2019

능동소나에서는 표적의 거리 도플러 정보를 탐지하기 위해 여러 가지 기법을 사용한다. 그중 압축 센싱을 적용한 기법은 기존의 방식보다 더욱 정밀한 탐지가 가능하며 우수한 성능을 나타낸다. 능동 소나의 거리 도플러 추정에 적용할 수 있는 압축 센싱 알고리즘은 여러 가지 있다. 압축 센싱 알고리즘 마다 계산 성능이 다르며 압축 센싱 알고리즘에 따라 신호 대 잡음비와 센싱 행렬의 코히런스가 거리 도플러 추정에 미치는 영향의 정도가 다르다. 본 논문은 능동 소나의 거리 도플러 추정을 위한 여러 가지 압축 센싱 알고리즘의 계산 성능과 정확도를 비교, 분석하였다. 여러 신호대 잡음비, 상호간섭성 값에 대한 OMP(Orthogonal Matching Pursuit), CoSaMP(Compressive Sampling Matching Pursuit), BPDN(CVX)(Basis Pursuit Denoising), LARS(Least Angle Regression) 알고리즘의 추정 성능을 확인하였으며, 상황에 따른 최적의 압축 센싱 알고리즘을 보인다.

• 대한기계학회논문집A
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• 제34권4호
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• pp.487-493
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• 2010

대부분의 구조해석 문제는 외부에서 주어진 하중에 대한 변형과 응력에 관심을 두고 있지만 많은 경우에서 표면 또는 내부에 주어진 응력이나 트랙션을 구하는 역문제 해석이 필요하게 된다. 본 연구에서는 구하고자 하는 트랙션에서 멀리 떨어진 영역의 변위를 측정하여 미지의 트랙션을 평가하는데 유한요소법을 사용한 역문제 수식화를 적용하였다. 일반적으로 역시스템의 불안정으로 인하여 측정 변위의 작은 오차는 해석 결과에 큰 영향을 주게 된다. 이와 같은 역시스템의 불안정성을 개선하기 위하여 본 연구에서는 구하고자 하는 트랙션에 가까운 단면의 변위를 Gram-Schmidt 수직화 기법을 통한 수직기저함수 사용하여 예측하고 보다 안정된 역문제를 해석하는 방법을 개발하였고 장점들을 수치 예제를 통하여 보여주었다.