• Journal of The Korean Astronomical Society
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• v.41 no.3
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• pp.77-81
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• 2008

As a continuation of a previous work by Park et al. (2006), we have developed a two-element radio interferometer that can measure both the phase and amplitude of a visibility function. Two small radio telescopes with diameters of 2.3 m are used as before, but this time an external reference oscillator is shared by the two telescopes so that the local oscillator frequencies are identical. We do not use a hardware correlator; instead we record signals from the two telescopes onto a PC and then perform software correlation. Complex visibilities are obtained toward the sun at ${\lambda}\;=\;21\;cm$, for 24 baselines with the use of the earth rotation and positional changes of one element, where the maximum baseline length projected onto UV plane is ${\sim}\;90{\lambda}$. As expected, the visibility amplitude decreases with the baseline length, while the phase is almost constant. The image obtained by the Fourier transformation of the visibility function nicely delineates the sun, which is barely resolved due to the limited baseline length. The experiment demonstrates that this system can be used as a "toy" interferometer at least for the education of (under)graduate students.

• ETRI Journal
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• v.33 no.1
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• pp.27-31
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• 2011

This paper addresses estimating the frequency of a cisoid in the presence of white Gaussian noise, which has numerous applications in communications, radar, sonar, and instrumentation and measurement. Due to the nonlinear nature of the frequency estimation problem, there is threshold effect, that is, large error estimates or outliers will occur at sufficiently low signal-to-noise ratio (SNR) conditions. Utilizing the ideas of averaging to increase SNR and weighted linear prediction, an optimal frequency estimator with smaller threshold SNR is developed. Computer simulations are included to compare its mean square error performance with that of the maximum likelihood (ML) estimator, improved weighted phase averager, generalized weighted linear predictor, and single weighted sample correlator as well as Cramer-Rao lower bound. In particular, with smaller computational requirement, the proposed estimator can achieve the same threshold and estimation performance of the ML method.

• ETRI Journal
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• v.20 no.1
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• pp.16-27
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• 1998

In this paper, we consider the acquisition performance of an IS-95 reverse link access channel slot as a function of system design parameters such as postdetection integration length and the number of access channel message block repetitons. The uncertainty region of the reverse link spreading codes compared to that of forward link is very small, since the uncertainty region of the reverse link is determined by a cell radius. Thus, the parallel acquisiton technique in the reverse link is more efficient than a serial acquisition technique in terms of implementation and of acquisition time. The parallel acquisition is achieved by a bank of N parallel I/Q noncoherent correlator are analyzed for band-limited noise and the Rayleigh fast fading channel. The detection probability is derived for multiple correct code-phase offsets and multipath fading. The probability of no message error is derived when rake combining, access channel message block combining, and Viterbi decoding are applied. Numerical results provide the acquisition performance for system design parameters such as postdetection integration length and number of access channel message block repetitions in case of a random access on a mobile station.

• Journal of Information Display
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• v.3 no.2
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• pp.19-25
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• 2002

In this paper, a new target extraction algorithm is proposed, in which the coordinates of target are obtained adaptively by using the difference image information and the optical BPEJTC(binary phase extraction joint transform correlator) with which the target object can be segmented from the input image and background noises are removed in the stereo vision system. First, the proposed algorithm extracts the target object by removing the background noises through the difference image information of the sequential left images and then controlls the pan/tilt and convergence angle of the stereo camera by using the coordinates of the target position obtained from the optical BPEJTC between the extracted target image and the input image. From some experimental results, it is found that the proposed algorithm can extract the target object from the input image with background noises and then, effectively track the target object in real time. Finally, a possibility of implementation of the adaptive stereo object tracking system by using the proposed algorithm is also suggested.

• Journal of Information Display
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• v.5 no.1
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• pp.41-46
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• 2004

In this paper, a new stereo 3D moving-target tracking system using the MSE (mean square error) and BPEJTC (binary phase extraction joint transform correlator) algorithms is proposed. A moving target is extracted from the sequential input stereo image by applying a region-based MSE algorithm following which, the location coordinates of a moving target in each frame are obtained through correlation between the extracted target image and the input stereo image by using the BPEJTC algorithm. Through several experiments performed with 20 frames of the stereo image pair with $640{\times}480$ pixels, we confirmed that the proposed system is capable of tracking a moving target at a relatively low error ratio of 1.29 % on average at real time.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.7
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• pp.48-55
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• 1992

In this paper, fSDF/POF, BPOF spatial matched filters are designed and implemented by CGH. The correlation characteristics for the suggested filters are analyzed for the distorted input images. Input patterns are obtained from the out-of-plane aircraft images by gradually rotating it, and then used for SDF training images. Modified version of LCD is used for a real-time input device of an optical correlator, and CGH-based fSDF filters are fabricated on film mask for spatial matched filter in order to recognize the distorted images. Total optical corrlator system size is effectively reduced to 148.8 cm by using lens combinations. Computer simulations and experimental results show that the suggested phase filters have nearly uniform correlation characteristics and have good classification capabilities between two classes.

• Korean Journal of Optics and Photonics
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• v.2 no.2
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• pp.83-88
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• 1991

Studies on space-invariant pattern recognition have been carried out from various approaches. Pattern recognition system using SDF filter, from weighted linear summation of tranining images, has been the focus of research since its first appearence. In this thesis, off-axis pSDF spatial matched filter has been constructed by combining angular multiplexing of off-axis reference plane wave with pSDF filter made from pseudo-inverse algorithm, and transformed to phase only filter. From observation of the correlation responses in the correlation plane, it is shown that proposed off-axis pSDF spatial matched filter is available to pattern classification and can be used for optical correlator.

• Journal of the Korean Society of Safety
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• v.11 no.2
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• pp.143-149
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• 1996

We propose an Opto-Digital hybrid fingerprint Identification system based on the binary phase extraction joint transform correlator(BPEJTC) for validation and security yerification. It is shown that since the BPEJTC provides higher peak-to-sidelobe ratio than that of the conventional JTC and does not cause correlation peaks due to intra-class association, this system is well-adaptive to the multiple object environments. Experimental results show that this system has a good performance in the presence of multiple images and the variations of the same person.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.303-306
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• 2006

A roll rate estimation method is proposed using the GPS measurement for spinning vehicles such as guided munitions and smart bombs. Before designing the roll rate estimator, the carrier phase and the carrier frequency deviation caused by spinning have been observed. Based on the observation, the spinning frequency is estimated using I and Q value from the correlator. The proposed method is evaluated through computer simulations using a software defined receiver and a GPS IF signal generator.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.395-398
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• 2006

In this paper, for implementing a real-time software GNSS receiver we propose the highly efficient and fast algorithms such as partial down-conversion, phase rotator, composite I&Q accumulation, Virtual DCO technique, and parallel acquisition using FFT. When the proposed algorithms are used, more 30 tracking channels with 3 tracking arm(early-prompt-late) is operated real-time on Intel 2.8GHz personal computer. Also, the partial down-conversion reduces the FFT size, for parallel acquisition, to 1/8 of conventional FFT-size and the program size includes map is not exceed 1Mbyte. Finally, the proposed real-time software GNSS receiver using the proposed algorithms provides the navigation solution with below 10 meter rms error.