• The Journal of the Korea institute of electronic communication sciences
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• v.4 no.1
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• pp.66-69
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• 2009

An adaptive echo canceller is necessary for an application such as a speakerphone, 3G image telephony and VoIP service system. These echo cancellers need to have many taps for filtering echo signals. Many taps cause computation data to increase and convergence speed to be low. To overcome these problems, An adaptive echo canceller with the advanced convergence speed is proposed in this paper. To improve the speed, we divide an echo band into subbands and place a subband filter to be adaptive for each subband. Each subband filter recognizes the echo signal as subband echo signals. So, dynamic range of subband is small, the convergence speed is fast. Moreover, as the number of Tap and weight update are estimated in each subband, the implementation complex of a adaptive filter is low.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.7C
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• pp.624-632
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• 2005

We consider an adaptive bit-loading technique for bit interleaved coded modulation-orthogonal frequency division multiplexing(BICM-OFDM) systems. By adjusting transmission parameter of each subcarrier adaptively depending on the subchannel state, the performance of OFDM system can be improved dramatically. In this paper, the number of bits for each subcarrier is allocated to minimize bit error rate keeping the constant throughput for the adaptive transmission technique of BICM-OFDM system which can be applied to real time transmission. Also, We use the discrete Lagrange multiplier method to get the optimum solution under the integer bit allocation constraint. Simulation results show that computational amount of the proposed bit allocation technique is not high and BICM-OfDM system using the proposed technique can get the SNR gain by 2$\~$3 dB over nonadaptive one.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.11
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• pp.1348-1358
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• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation fur flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among seven filling patterns at each tetrahedral control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. The collapse of a water dam and the filling of a fluidity spiral have been analyzed. The numerical results have been in good agreement with the experimental results and the efficiency of the adaptive grid refinement and filling pattern techniques have been verified.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.1C
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• pp.1-8
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• 2007

LMS(Least Mean Square) algorithm using steepest descent way in adaptive signal processing requires simple equation and is used widely because of the less complexity. But eigenvalues change by width of input signals in time domain, so the rate of convergence becomes low. In this paper, we propose a new fast running FIR filter structure that improves the convergence speed of adaptive signal processing and the same performance as the existing fast wavelet transform algorithm with less computational complexity. The proposed filter structure is applied to wavelet based adaptive algorithm. Simulation results show a better performance than the existing one.

• Journal of Advanced Navigation Technology
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• v.6 no.4
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• pp.306-311
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• 2002

In this paper, we have proposed the Multi-Carrier (MC) CDMA system by adopting multi-interference cancellation techniques connecting an adaptive array antenna and a CCI canceller in cascade form. And, we have analyzed the BER performance of system in AWGN channel where MUI is a major interference degrading the performance of the proposed MC CDMA system. Also, we have evaluated the degree of performance improvement in the proposed MC CDMA system. As the result of analysis, a CCI canceller is better efficient than an adaptive array antenna in the performance improvement and that the performance improvement becomes large as the number of users increases when multi-interference cancellation techniques are used in cascade form. Also, we found that performance of $10^{-5}$ in a point of view BER could be achieved when $E_b/N_o$ is more than 10 dB.

• Smart Structures and Systems
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• v.31 no.5
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• pp.437-454
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• 2023

Real-time hybrid simulation (RTHS), which has the advantages of a substructure pseudo-dynamic test, is widely used to investigate the rate-dependent mechanical response of structures under earthquake excitation. However, time delay in RTHS can cause inaccurate results and experimental instabilities. Thus, this study proposes a model-based adaptive control strategy using a Kalman filter (KF) to minimize the time delay and improve RTHS stability and accuracy. In this method, the adaptive control strategy consists of three parts-a feedforward controller based on the discrete inverse model of a servohydraulic actuator and physical specimen, a parameter estimator using the KF, and a feedback controller. The KF with the feedforward controller can significantly reduce the variable time delay due to its fast convergence and high sensitivity to the error between the desired displacement and the measured one. The feedback control can remedy the residual time delay and minimize the method's dependence on the inverse model, thereby improving the robustness of the proposed control method. The tracking performance and parametric studies are conducted using the benchmark problem in RTHS. The results reveal that better tracking performance can be obtained, and the KF's initial settings have limited influence on the proposed strategy. Virtual RTHSs are conducted with linear and nonlinear physical substructures, respectively, and the results indicate brilliant tracking performance and superb robustness of the proposed method.

• The Journal of the Acoustical Society of Korea
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• v.28 no.3
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• pp.245-250
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• 2009

In communications and signal processing area, a number of least mean square adaptive algorithms have been used because of simplicity and robustness. However the LMS algorithm is known to have slow and non-uniform convergence. Various variable step size LMS adaptive algorithms have been introduced and researched to speed up the convergence rate. A variable step size LMS algorithm using the error difference for updating the step size is proposed. Compared with other algorithms, simulation results show that the proposed LMS algorithm has a fast convergence. The theoretical performance of the proposed algorithm is also analyzed for the steady state.

• Journal of Broadcast Engineering
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• v.2 no.2
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• pp.194-205
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• 1997

In video compression standards such as MPEG and H.263. rate control is one of the key components for good coding performance. This paper presents a simple adaptive rate control scheme using a piecewise linear approximation model. While conventional buffer control approach is performed by adjusting the quantization parameter linearly according to the buffer fullness. the proposed approach uses a piecewise linear approximation model derived from logarithmic relation between the quantization parameter and bitrate in data compression. In addition. a forward analyzer performed in the spatial domain is used to improve image quality. Simulation results demonstrate that the proposed method provides better performance than the conventional one and reduces the fluctuation of the PSNR per frame while maintaining the quality of the reconstructed frames at a relatively stable level.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.7
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• pp.500-507
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• 2018

A three-channel radio frequency (RF) monopulse receiver using a data signal with a maximum transmission rate of 274 Mbps was designed. A monopulse receiver using a broadband communication signal was designed to operate in the Ku band, and it consists of a down-conversion module and a signal-processing module. To satisfy the performance of the proposed RF monopulse receiver, a signal-processing function less than the reception sensitivity for each transmission rate according to the adaptive transmission rate is required. To minimize signal reception and mutual frequency interference of various bandwidths, two RF filters were applied. To verify the satisfaction of system requirements, an AWR Corp. simulation tool was used.

• Journal of Korea Multimedia Society
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• v.7 no.8
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• pp.1078-1085
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• 2004

The SARLM(Source Adaptive Receiver-Driven Multi-Layered Multicast) has been proposed to address heterogeneous bandwidth constraints through layer merging and splitting. However, this method causes that receivers subscribing to the higher layer drop down to the lower layer and hence may decrease utilization of available bandwidth after layer merging. In this paper, we proposed a multicast regrouping method considering distributive status of receivers according to loss rates. The proposed method weights receivers according to loss rates. And then it groups higher layer with receivers subscribing to lower layer have extra bandwidth and lower layer with receivers subscribing to higher layer have high loss rate. Experimental results show that receivers subscribing to higher layer can receive in high transmission rate and consequently the proposed method effectively improves utilization of available bandwidth.