Jinho Choi

On estimating the direction of arrival when the number of signal sources is unknown

Abstract A new problem, estimation of the direction of arrival (DOA) without knowing (or assuming) the number of signal sources, is addressed. In this paper we propose a method which is related to both the multiple signal classification (MUSIC) and Capons methods. The performance of the proposed method when the number of signal sources is unknown is shown to be almost the same as that of the MUSIC method when the number of signal sources is exactly known. In addition, from the statistical properties, it is observed that the estimation error of the proposed method has almost the same variance as the MUSIC method, although the proposed method yields a slightly biased estimate.

Modification of the reference signal for fast convergence in LMS-based adaptive equalizers

In adaptive equalizers based on least mean squares (LMS) algorithms, the convergence rate is determined by the correlation matrix of an input signal. When the eigenvalue spread of the correlation matrix is close to unity, the convergence rate is quite fast. In this paper, for fast convergence of LMS-based adaptive equalizers we propose a modified reference signal pertinent to the given statistical channel. From the theoretical analysis and computer simulations, it is shown that the proposed modification method is guile effective for fast convergence of LMS-based adaptive equalizers. >

Asymptotic distribution of the MUSIC null spectrum

The asymptotic distribution of the MUSIC null spectrum at the source location is derived. It is shown that the asymptotic distribution of the MUSIC null spectrum has a x/sup 2/ distribution: the asymptotic mean and variance of the MUSIC null spectrum depend on the degree of freedom that is two times the difference between the number of sensors and that of signals. From this result, explicit expressions for the asymptotic variance of the MUSIC null spectrum are obtained. The result is a simpler alternative to and a special case of the result obtained independently by H. Lee and M. Wengrovitz (see ibid., vol.39, no.6, p.1333, 1991). >

A combined determination-estimation method for direction of arrival estimation

Abstract A combined determination-estimation method is proposed for direction finding of multiple source locations in this paper. The method is based on the conditional mean multiple signal classification (MUSIC) null-spectrum, and does not require a priori decision on the number of signal sources. It is shown that the shapes of the MUSIC and conditional mean MUSIC null-spectra are not quite different. To see the resolution performance, the probability of resolution (PR) of the MUSIC null-spectrum and that of the conditional mean MUSIC null-spectrum are obtained by computer simulation, from which it is seen that the PRs of these two null-spectra are almost the same. In addition it is found that the information theoretic criterion and Bayesian approach (maximum a posteriori estimation method) for determining the number of signal sources would give the same result.

A statistical analysis of MUSIC null-spectrum via decomposition of estimation error

Abstract A statistical performance analysis of the multiple signal classification (MUSIC) method is addressed in this paper. To obtain the first and second order statistics of the sample MUSIC null-spectrum at the directions of arrival, a method which does not require the eigendecomposition is considered for the two signal sources case. From this result we obtain a more exact expression of the resolution threshold which is then used to evaluate the resolution capability for two closely located signal sources.

A generalized null-spectrum for direction of arrival estimation

A generalization of null-spectrum for the estimation of directions of arrival of signal sources is considered. The upper and lower bounds of a class of the generalized null-spectrum, the maximum and minimum null-spectra, are derived. The authors observe that the maximum null-spectrum has higher resolution capability than other null-spectra including the multiple signal classification and Min-Norm null-spectra. In addition, it is seen that the estimates of the direction of arrival obtained by using the maximum and multiple signal classification null-spectra have the same asymptotic distribution. Through computer simulation the probabilities of resolution of various null-spectra are obtained, from which they confirmed the resolution capability of the maximum null-spectrum. >

Some convergence properties of Godard's quartic algorithm

Abstract Convergence analysis on Godards quartic (GQ) algorithm used for blind equalization is accomplished. The first main result is an explanation of the local behavior of the GQ algorithm around the global minimum point of the average performance function. From this result, we can determine the adaptation gain and compare the convergence rate with that of the decision directed (DD) algorithm. It is shown that the convergence rate of the GQ algorithm is faster than that of the DD equalization algorithm. The second main result is a description of the geometry of the average performance function: the region of attraction is observed to depend on the characteristics of the channel as well as the statistics of the input signal. It is shown that a good initial parameter vector of the GQ algorithm can be chosen based on the information of the geometry of the average performance function.

Direction of arrival estimation with unknown number of signal sources

A new problem, estimation of the direction of arrival (DOA) without knowing (or assuming) the number of signal sources, is addressed. The authors propose a method which is related to both the multiple signal classification (MUSIC) and Capons methods. The performance of the proposed method when the number of signal sources is unknown is shown to be almost the same as that of the MUSIC method when the number of signal sources is exactly known.<<ETX>>

Growth and Brilliant Photo-Emission of Crystalline Hexagonal Column of Alq3 Microwires

We report the growth and nanoscale luminescence characteristics of 8-hydroxyquinolinato aluminum (Alq3) with a crystalline hexagonal column morphology. Pristine Alq3 nanoparticles (NPs) were prepared using a conventional reprecipitation method. Crystal hexagonal columns of Alq3 were grown by using a surfactant-assisted self-assembly technique as an adjunct to the aforementioned reprecipitation method. The formation and structural properties of the crystalline and non-crystalline Alq3 NPs were analyzed with scanning electron microscopy and X-ray diffraction. The nanoscale photoluminescence (PL) characteristics and the luminescence color of the Alq3 single NPs and their crystal microwires (MWs) were evaluated from color charge-coupled device images acquired using a high-resolution laser confocal microscope. In comparison with the Alq3 NPs, the crystalline MWs exhibited a very bright and sharp emission. This enhanced and sharp emission from the crystalline Alq3 single MWs originated from effective π-π stacking of the Alq3 molecules due to strong interactions in the crystalline structure.