• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 1996.06a
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• pp.3-7
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• 1996

In this paper, the performances of OFDM and MC-CDMA systems in a slowly-varying multipath fading environment is investigated. Time variation of the multipath channel leads to both a change of an optimal coefficient in one-tap equalizer and a loss of subchannel orthogornality, resulting in significant performance loss. A new simple one-tap equalizer which can reduce the effect of slowly time-varying multipath channel is proposed by taking into account time-variation of multipath profile and modifying the previous equalization techniques. It is demonstrated by computer simulation that the performances of OFDM and MC-CDMA systems can be improved by using the proposed one-tap equalizers when the multipath channel is slowly varying.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.6B
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• pp.1082-1091
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• 2000

In this paper, the efficient equalization method for OFDM(Orthogonal Frequency Division Multiflexing) System using the QAM(Quadrature Amplitude Modulation) in multipath fading channel is proposed in order to faster and more efficiently equalize the received signals that are sent over real channel. In generally, the one-tap linear equalizers have been used in the frequency-domain as the existing equalization method for OFDM system. In this technique, if characteristics of the channel are changed fast, the one-tap linear equalizers cannot compensate for the distortion due to time variant multipath channels. Therefore, in this paper, we use one-tap non-linear equalizers instead of using one-tap linear equalizers in the frequency-domain, and also use the linear equalizer in the time-domain to compensate the rapid performance reduction at the low SNR(Signal-to-Noise Ratio) that is the disadvantage of the non-linear equalizer. In the frequency-domain, when QAM signals, consisting of in-phase components and quadrature (out-phase) components, are sent over the complex channel, the only in-phase and quadrature components of signals distorted by the multipath fading are changed the same as signals distorted by the noise. So the cross components are canceled in the frequency-domain equalizer. The time-domain equalizer and the adaptive algorithm that has lower-error probability and fast convergence speed are applied to compensate for the error that is caused by canceling the cross components in the frequency-domain equalizer. In the time-domain, To compensate for the performance of frequency-domain equalizer the time-domain equalizes the distorted signals at a frame by using the Gold-code as a training sequence in the receiver after the Gold-codes are inserted into the guard signal in the transmitter. By using the proposed equalization method, we can achieve faster and more efficient equalization method that has the reduced computational complexity and improved performance.

• Proceedings of the KIEE Conference
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• 1999.07g
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• pp.3135-3137
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• 1999

We propose two robust blind equalization algorithms based on multi-stage clustering blind equalization algorithm, which are called a complex classification update algorithm(CCUA) and an error compensation algorithm(ECA). The first algorithm is a tap-updating algorithm which each computes classified real and imaginary parts in order to reduce computations and the complexity of implementation as a stage increase. The second one is a algorithm which can achieve faster convergence speed because error of equalizer input make always fixed. Test results confirm that the proposed algorithms with faster convergence and lower complexity outperforms both constant modulus algorithm (CMA) and conventional multi-stage blind clustering algorithm(MSA) in reducing the SER as well as the MSE at the equalizer output.

• Journal of Korea Multimedia Society
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• v.12 no.9
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• pp.1316-1322
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• 2009

The multicarrier system is in the limelight for broadband wireless communications due to its spectral efficiency. Filtered multitone(FMT) system uses a filter that has several symbol periods duration. Using long-period filter causes a performance degradation because of intersymbol interference in multipath fading channels. In this paper, we propose a simple equalization method which can reduce the ISI due to the wireless channels. The proposed equalization method compensates the ISI by subtracting the estimated ISI components from the current symbol using one-tap equalizer. The performance of the proposed system is verified through theoretical analysis and simulation results show that the proposed system can mitigate the effect of ISI significantly.

• Journal of the Korea Society for Simulation
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• v.20 no.4
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• pp.91-96
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• 2011

As the user's demand for ultra high-speed wireless internet has increased, the standardization, research and development of future mobile communication systems have been done for several years. IMT-Advanced system which is called fourth generation mobile communication should support the data rate of 1 Gbps for nomadic users and 100 Mbps for mobile users. Also, the system should hold call connection at the mobile speed of 350 km/h. Meanwhile, since Doppler spread is linearly proportional to mobile speed, high mobility leads to the increase of interference between subcarriers and the deterioration of detection performance consequently. In this paper, we evaluate and analyze detection probability with respect to equalization methods in time-varying channels under system parameters complying with IMT-Advanced requirements. According to computer simulation conducted by varying mobile speed and code rate, MMSE based equalization can mitigate performance degradation of IMT-Advanced system considerably in time-varying channels.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.1
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• pp.91-101
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• 2014

Three water treatment plants(WTPs) in Jeju island whose source water have different characteristics from those of the mainland of Korea were investigated. Coefficients of bulk water decay($k_b$) of free chlorine at $5^{\circ}C$ for ES, GJ, NW WTPs were $-0.003hr^{-1}$, $-0.002hr^{-1}$ and $-0.001hr^{-1}$ respectively based on bottle tests. To simulate the free chlorine variations in the distribution system using EPANET, ES WTP was chosen. Free chlorine concentrations of several sites were less than the drinking water quality standards(i.e., 0.1 mg/L); E5(0.03 mg/L), E6(0.02 mg/L), W21(0.02 mg/L) and W25(0.03 mg/L). To maintain more than 0.1 mg/L of free chlorine in the distribution system, at least 1.9 mg/L of chlorine was needed at the WTP, which suggested rechlorination was needed to supply palatable tap water to customers. Two sites, one that diverged into E5 and E6 in the east-line and another located before E21 in the west-line were selected for the appropriate rechlorination locations. The recommended rechlorination dosages were 0.42 mg/L for the east and 0.27 mg/L for the west. The simulated results indicated that the free chlorine could be reduced to 0.4 mg/L at the WTP with rechlorination, and taps with excessive free chlorine could be more stabilized(i.e., 0.1~0.4 mg/L).

• ETRI Journal
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• v.31 no.6
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• pp.770-777
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• 2009

We have developed a fully functional reconfigurable optical add-drop multiplexer (ROADM) switch module using a polymer integrated photonic lightwave circuit technology. The polymer variable optical attenuator (VOA) array and digital optical switch array are integrated into one polymer PLC chip and packaged to form a 10-channel VOA integrated optical switch module. Four of these optical switch modules are used in the ROADM switch module to execute 40-channel switching and power equalization. As a wavelength division multiplexer (WDM) filter device, two C-band 40-channel athermal arrayed waveguide grating WDMs are used in the ROADM module. Optical power monitoring of each channel is carried out using a 5% tap PD. A controller and firmware having the functions of a 40-channel switch and VOA control, optical power monitoring, as well as TEC temperature control, and data communication interfaces are also developed in this study.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.8B
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• pp.745-751
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• 2002

The performance of existing CDMA-type multiple access data transmission systems is limited by interferences due to adverse mobile communication channel characteristics. Among them, the multi-user interference becomes one of the major performance degradation factors because the signal-to-signal orthogonality can be easily perturbed when numerous user signals are distorted by multipath fading channels and mixed together. In order to enhance the performance of CDMA-type systems by suppressing the multi-user interference, we have adopted chip-based cyclic prefix insertion along with adaptive one-tap DFE equalization into MC-DS-CDMA, which is known for its robustness in the frequency selective multipath fading channel environment. In order to assess the performance of the proposed system, a set of computer simulations is performed in the reverse link in which each user signal undergoes different multipath Rayleigh fading. The results show us a superior performance of our system over other CDMA systems in terms of SNR to BER measurements.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.9A
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• pp.830-837
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• 2005

ISI is caused by delay spread in the multipath channel environment. There are two kinds of channel equalizer: Linear and Non-Linear type according to the structures. In this paper, we propose an improved adaptive linear equalizer to mitigate ISI. The proposed adaptive equalizer is constructed by using asymmetrical Dsmvenu filter based on USE sub-optimal receiver. Asymmetrical structure of the transversal filter is realized by moving the main tap position from center to side. If this structure is used, we can divide ISI to precusor and postcusor. As a result the proposed equalizer has a larger extended compensation range than conventional adaptive linear equalizer. In computer simulation, we compare the bit error rate performance of the proposed linear equalizer with the conventional one on the S-V channel which is modeled for WB systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.138-145
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• 2007

Wireless transmission system using the multipath channel is affected ISI due to the delay spread. So we use a decision feedback equalizer which consist of decision part and feedback filter for remove the ISI effectively. In this paper, we propose a improved adaptive decision feedback equalizer to mitigate ISI effectively. The proposed adaptive decision feedback equalizer is construct by using soft decision device and hierarchical feedback filter based on MMSE sub-optimal equalizer using the LMS algorithm. Soft decision device mitigate the error propagation in feedback filter by incorrectly detected decision symbol and feedback filter which is divided two step independently mitigate the ISI by using a adaptive algorithm. As a result this structure shows better performance than conventional decision feedback equalizer by mitigating the error propagation in filter cause incorrectly detecting symbol. and we get the MSE more rapidly by using larger step-size due to reduce the number of feedback filter tap. In computer simulation, we compare the bit error rate performance of proposed decision feedback equalizer with conventional one on the S-V channel model for UWB system.