• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1471-1479
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• 1999

This paper presents an adaptive beamforming algorithm for an MC-CDMA system with an adaptive array antenna. By employing an antenna array at the receiver of an MC-CDMA system, the performance of an MC-CDMA system, which is known to be effective for high data rate transmission due to its robustness to multipath fading and its simplicity for using a simple one-tap equalizer, is shown to be significantly improved. The proposed algorithm for adaptive beanforming in an MC-CDMA system is derived by (1) calculating the error signals between the pilot symbols of desired user and the received pilot signals in frequency domain, (2) transforming the frequency-domain error signals into time-domain error signals, (3) updating the filter coefficients of the adaptive beamformer in the direction of minimizing the MSE. Convergence behavior and performance improvement of the proposed approach are demonstrated through computer simulation by applying it to the conventional MC-CDMA system.

• Journal of the Korean Institute of Intelligent Systems
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• v.18 no.2
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• pp.163-168
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• 2008

Navigation system based on indoor location estimation is one of the core technologies in mobile robot systems. Wireless sensor network has great potential in the indoor location estimation due to its characteristics such as low power consumption, low cost, and simplicity. In this paper we present an algorithm to estimate the indoor location of mobile robot based on wireless sensor network and fuzzy modeling. ZigBee-based sensor network usually uses RSSI(Received Signal Strength Indication) values to measure the distance between two sensor nodes, which are affected by signal distortion, reflection, channel fading, and path loss. Therefore we need a proper correction method to obtain accurate distance information with RSSI. We develop the fuzzy distance models based on RSSI values and an efficient algorithm to estimate the robot location which applies to the navigation algorithm incorporating the time-varying data of environmental conditions which are received from the wireless sensor network.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.10 s.340
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• pp.1-8
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• 2005

This Paper Proposes the algorithm for improving the Performance or symbol timing synchronization in hoc terrestrial DTV system. The Gardner algerian is used for symbol timing synchronization has good performance in multipath fading environment but degradation of performance is caused by jitter. Though the amount of jitter becomes more little as narrow bandwidth of loop Inter, convergence speed becomes slower. This paper propose the algorithm that averages out values of loop filter every certain time and gradually reduces the bandwidth of loop filter after estimating offset using this average for the high speed of convergence and reducing the met of jitter. The proposed algorithm has better performance with high speed of convergence and the amount of jitter than conventional method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.4
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• pp.379-386
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• 2004

OFDM(orthogonal frequency division multiplexing) communications system is very attractive for the high data rate transmissionin the frequency selective fading channel. Since OFDM has high PAPR(peak-to-average power ratio), OFDM signal may be distorted by the nonlinear HPA(high power amplifier). In this paper, we propose an improved dummy sequence scheme for reducing the PAPR in OFDM communication system. This method inserts each different dummy sequence at the predefined sub-carriers fur PAPR reduction. After IFFT, the OFDM data signal with the lowest PAPR is selected to transmit. The complementary sequence is used as dummy sequence. So, it can cut down the computation time and quantity because it dose not require the peak value optimization for finding the phase rotation factor and the transmission of the side information about the rotation factor unlike the PTS method.

• The Journal of Information Technology
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• v.5 no.4
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• pp.1-8
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• 2002

This thesis is about power line communication(PLC) over the low voltage grid. The main advantage with power line communication is the use of an existing infrastructure. The PLC channel can be modeled as having multi-path propagation with frequency-selective fading, typical power lines exhibit signal attenuation increasing with length and frequency. OFDM(Orthogonal Frequency Division Multiplexing) is a modulation technique where multiple low data rate carriers are combined by a transmitter to form a composite high data rate transmission. To implement the multiple carrier scheme using a bank of parallel modulators would not be very efficient in analog hardware. Each carrier in an OFDM is a sinusoid with a frequency that is an integer multiple of a base or fundamental sinusoid frequency. Therefore, each carrier is a like a Fourier series component of the composite signal. In fact, it will be shown later that an OFDM signal is created in the frequency domain, and then transformed into the time domain via the Discrete Fourier Transform(DFT).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.2A
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• pp.137-145
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• 2002

In the method of 3D modeling, stereo matching method which obtains three dimensional depth information from the two images is taken from the different view points. In general, it is very essential work for the 3D modeling from 2D stereo images to estimate the exact disparity through fading the conjugate pair of pixel from the left and right image. In this paper to solve the problems of the stereo image disparity estimation, we introduce a novel approach method to improve the exactness and efficiency of the disparity. In the first place, we perform a wavelet transformation of the stereo images and set the reference points in the image by the feature-based matching method. This reference points have very high probability over 95 %. In the base of these reference points we can decide the size of the variable block searching windows for estimating dense disparity of area based method and perform the ordering constraint to prevent mismatching. By doing this, we could estimate the disparity in a short time and solve the occlusion caused by applying the fried-sized windows and probable error caused by repeating patterns.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1348-1356
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• 2000

In this paper, we proposed a trellis coded Multi-Carrier CDMA 16 QAM system with multiple transmit/receive antenna diversity technique, which is simple and suitable for indoor wireless communications. The proposed multiple transmit/receive antenna diversity technique is that the transmitter sends a trellis coded Multi-Carrier CDMA 16 QAM signal from multiple transmitting antennas with intentional time delays, which makes a receiver possible to distinguish and combine the signals from different antennas. In wireless indoor communication system, if we allow the increase of the complexity of the system, it is also possible to achieve additional diversity gain in the performance with the combination of the proposed technique and the conventional receiving antenna diversity. Furthermore, we have found that the proposed trellis coded Multi-Carrier CDMA 16 QAM system, which employs multiple transmit/receive antenna, is less sensitive to the multiple user interference and fading than conventional receiving antenna diversity systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.5C
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• pp.469-477
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• 2007

Most multimedia source coders exhibit unequal bit error sensitivity. Efficient transmission system design should therefore incorporate the use of matching unequal error protection (UEP). In this paper, we present and evaluate a flexible space-time coding system with unequal error protection. Multiple transmit and receive antennas and bit-interleaved coded modulation techniques are used combined with rate compatible punctured convolutional codes. A near optimum iterative receiver is employed with a multiple-in multiple-out inverse mapper and a MAP decoder as component decoders. We illustrate how the UEP system gain can be achieved either as a power or bandwidth gain compared to the equal error protection system (EEP) for the identical source and equal overall quality for both the UEP and EEP systems. An example with two/three transmit and two receive antennas using BPSK modulation is given for the block fading channel.

• Fashion & Textile Research Journal
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• v.8 no.3
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• pp.343-348
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• 2006

This study aims to attain gray tone dyed goods by using tannin that is contained in green tea. Tannin is given general name of polyphenol, which has a characteristic that bonds with protein and it is used for food preservative that protects against bacteria, as well as its purpose of black tone dye for silk treatment that has been processed since its early ages. In particular, as tannin reacts with all kinds of metallic mordant and changes to various colors, when tannin acid is combined with iron, it becomes tannin steel and produces gray tone color. Tannin that is contained in green tea is condensed tannins and its structure does not hydrolyze, thus having flavan type structure. In order to find the suitable condition for processing tannin, UV-Vis part absorption spectrum of green tea tannin, dye ability based on temperature and time, reflection rate based on concentration, color changes based on acid treatment and alkali treatment, changes on surface based on concentration or metal mordant condition, and lightfastness were measured. Maximum absorption wavelength (${\lambda}_{max}$) of green tea tannin was at around 273nm, while strong absorption was also observed at below 350 nm. Dye ability of green tea tannin is done more easily on silk rather than cellulose fibers such as cotton, while the optimum condition for dyeing was observed to be at $60^{\circ}C$, for 20 minutes. As a result of acid treatment, the color of dye material consisted highly of gray tones and showed overall gray tone with the combined color of yellow and red after the alkali treatment. While it was observed that as dye concentration and metal mordant concentration increased, the color changed at counter-clockwise direction on the Y-scale of Munsell's scale of colors. Additionally, lightfastness was more on a normal fading.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.7A
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• pp.689-695
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• 2006

This paper focuses on the accurate performance evaluation of cooperative diversity technique with imperfect channel estimates. The channel environment for simulations and performance evaluation is supposed to be the slowly time-varying Rayleigh fading channel. The framework of the performance evaluation is based on the Moment Generating Function(MGF) approach. To apply the effect of this channel estimation error into the performance evaluation, we import an useful Gaussian approximation in formulating the effective noise component and the additive noise. The average BER performance of cooperative diversity with M-PSK and M-QAM is computed as a function of the ratio of the signal to the effective noise based on the approximation. The verification of computed performance is provided with simulations. The evaluated performance matches up to simulation results even in a low SNR region.