• 전자공학회논문지B
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• 제32B권7호
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• pp.989-1002
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• 1995

In this paper, we propose a new algorithm, so called the Signal Decorrelation via Virtual Translation of Array (SDVTA) algorithm, for estimating the directions of arrival(DOA's) of narrowband coherent signals incident on a general array. An effective procedure is composed of transforming the steering matrix of the original array into that of the virtually translated sensor array and taking the average of the transformed covariance matrices in order to decorrelate the coherent signals. The advantage of this approach is in that 1) it can estimate the DOA's of m-1 coherent signals(M : the number of array sensors) since the effective aperture size is never reduced. 2) a geometry of array is unrestricted for solving the narrowband coherency problem. 3) the efficiency of signal decorrelation does not depend on the phase differences between coherent signals unlike the Coherent Signal Subspace Method (CSM). Simulation results are illustrated to demonstrate the superior performance of this new algorithm in comparison with the normal MUSIC and examine the comparative performance with the various choices of the optimal transformation matrix under coherent signal environments.

• 소음진동
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• 제9권5호
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• pp.922-927
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• 1999

The objective of this paper is to obtain the contribution of each source to the spectrum of pressure, when there are multiple incoherent sources in near-field acoustic holography. For this objective, we have to obtain signals very coherent to the input signals of the sources. To obtain the very coherent signals, many people have measured pressure signals in the vincinity of the sources. However, it is sometimes difficult to locate microphones near to the sources so that the signals are very coherent to the input signals. This paper proposed a method to obtain the very coherent signals by near-field acoustic holography. Therefore, the proposed method does not require the measurement of pressure near to each source. Simulation results for two incoherent monopole sources showed the possibility of the proposed method.

• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1738-1746
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• 2004

When there are low signal to noise relationships or low coherences between measured pressure and a reference sensor, a pressure field measured and estimated by NAH (Nearfield Acoustic Holography) becomes noisy on the hologram and source planes. This paper proposes a method to obtain the high coherent de-noised pressure signals from low coherent noisy ones by combining a wavelet algorithm with NAH. The proposed method obtains the de-noised field from acoustic fields on a noise source plane reconstructed through backward propagation of NAH. Thus this method does not need high coherent pressure signals on the hologram surface while the conventional nearfield acoustic holography requires high-coherent signals. The proposed method was verified by numerical simulation using noisy signals, composed of original signals and imposed noises distributed on the hologram surface.

• 전자공학회논문지
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• 제53권8호
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• pp.95-104
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• 2016

배열 안테나를 이용한 부공간 (subspace) 기반의 도래각 추정 알고리즘은 다중 경로에 의해 나타나는 coherent 신호가 입사하는 경우 원 신호 공분산 행렬의 특이성 (singularity)으로 인해 도래각 추정 정확도가 급격히 감소한다. Coherent 신호에 의한 도래각 추정 알고리즘의 성능 저하를 극복하기 위해 제안된 공간 차이 기법 (spatial differencing method)은 coherent 신호의 도래각 추정뿐만 아니라 안테나 개수 이상의 신호원을 추정하는 기법으로 주목받았다. 그러나, 공간 차이 기법은 수신 신호의 유한한 표본 수에 의해 발생하는 uncorrelated 신호 간의 상관관계 (correlation)에 따라 도래각 추정 성능이 크게 영향을 받는 구조적 문제가 존재한다. 이러한 문제를 극복하기 위해, 본 논문에서는 획득한 수신 신호의 정보를 최대한 활용하여 uncorrelated 신호간의 상관관계를 효과적으로 제거하는 일반화된 공간 차이 기법을 제안한다. 그리고 모의실험을 통해 도래각 추정 정확도와 추정 가능 신호원의 수의 관점에서 성능을 평가하여 제안한 기법의 우수성을 입증한다.

• 전자공학회논문지
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• 제49권9호
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• pp.164-171
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• 2012

센서 어레이(sensor array)가 천이불변(shift invariance) 성질을 가질 때, ESPRIT(Estimation of Signal Parameter via Rotational Invariance Techniques) 방식은 이를 이용하여 어레이에 도래하는 신호의 도래각을 추정한다. 본 논문에서는 ESPRIT 방식을 적용하여 코히런트 신호의 도래각을 효과적으로 추정하는 방법을 제시한다. ESPRIT 방식은 신호부공간(signal subspace)을 이용한다. 코히런트 신호가 존재할 때, 신호부공간을 구하는 방법으로 SS(spatial smoothing) 방식이 널리 알려져 있으나 계산이 매우 복잡하다. 최근에 발표된 CV(correlation vector)에 기초한 방식은 계산은 간단하지만 SS 방식보다 작은 수의 신호를 분해한다. 제안 방식은 상관행렬의 일부를 이용하여 신호부공간을 구성하여 도래각을 추정한다. SS 방식과 비교하여, 제안 방식에서는 분해 가능한 신호의 수는 동일하면서 계산량을 크게 줄일 수 있다.

• 한국군사과학기술학회지
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• 제12권1호
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• pp.97-105
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• 2009

In this paper, the performance of AP(Alternating Projection) and EM(Expectation Maximization) algorithms is investigated in terms of detection of multiple signals, resolvability of coherent signals and the efficiency of sensor array processing. The basic idea of these algorithms is utilization of relaxation technique of successive 1D maximization to solve a direction finding problem by maximizing the multidimensional likelihood function. It means that the function is maximized over only for a single parameter while the other parameters are fixed at each step of the iteration. According to simulation results, the algorithms showed good performance for both incoherent and coherent multiple signals. Moreover, some advantages are identified for direction finding with very small samples and fast convergence. The performance of AP algorithm is compared with that of EM using multiple criteria such as the number of sensor, SNR, the number of samples, and convergence speed over uniform circular array. It is resulted AP algorithm is superior to EM overally except for one criterion, convergence speed. Especially, for EM algorithm there is no performance difference between incoherent and coherent case. In conclusion, AP and EM are viable and practical alternatives, which can be applied to a direction under due to the resolvability of multi-path signals, reliable performance and no troublesome eigen-decomposition of the sample-covariance matrix.

• 한국통신학회논문지
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• 제22권3호
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• pp.515-523
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• 1997

A high resolution algorithm is presented for resolving multiple coherent spread spectrum signals that are incident on an equispaced linear array. Unlike the conventional noise-eigenvector based methods, this algorithm makes use of the signal eigenvectors of the array spectral density matrix that are associates with eigenvalues that are larger than the sensor noise level. Simulation results are shown to demonstate the high performance of the proposed approach in comparison with MUSIC in which coherent signal subspace method (CSM) is employed.

• Journal of Communications and Networks
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• 제15권6호
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• pp.569-575
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• 2013

In this paper, we present a photonic approach for generating highly stable coherent sub-terahertz (THz) signals for wireless communications. As proof-of-concept we transmit data at 100 GHz carrier frequency using on-off keying modulation and heterodyne detection. The sub-THz carrier signals are generated by photo-mixing two optical carrier signals at different frequencies, extracted from an optical frequency comb. We introduce a novel system to stabilize the phase of the optical carrier signals. Error-free transmission is successfully achieved up to a bit rate of 8.5 Gbit/s at 100 GHz.

• 한국통신학회:학술대회논문집
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• 한국통신학회 1988년도 추계학술발표회 논문집
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• pp.223-226
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• 1988

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.153-156
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• 2005

This paper concerns an efficient iterative approach for eliminating coherent interference signals in linearly constrained adaptive arrays. The Alternate Mainbeam Nulling Algorithm[1] is implemented iteratively to find an optimum weight vector. The convergence parameters in the unit gain and null constraints are calculated using steepest descent method with gradient estimation. The nulling performance of the proposed method is compared with that of conventional ones. It is shown that the proposed method performs better than conventional ones when the power of the coherent signals is large compared with a desired signal. Also, it performs consistently well for more number of interferences.