• Publications of The Korean Astronomical Society
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• v.24 no.1
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• pp.65-81
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• 2009

We present the performance test results of VLBI Correlation Subsystem (VCS) trial product which was being developed for 1 year from August 2007. It is a core component of Korea-Japan Joint VLBI Correlator (KJJVC). The aim for developing VCS trial product is to improve the performance of VCS main product to reduce the efforts and cost, and to solve the design problems by performing the preliminary test of the manufactured trial product. The function of VCS trial product is that it is able to process the 2 stations-1 baseline, 8 Gbps/station speed, 1.2 Gbps output speed with FX-type. VCS trial product consists of Read Data Control Board (RDC), Fourier Transform Board (FTB), and Correlation and Accumulation Board (CAB). Almost main functions are integrated in the FTB and CAB board. In order to confirm the performance of VCS trial product functions, the spectral analysis, delay compensation and correlation processing experiments were carried out by using simulation and real observation data. We found that the overflow problem of re-quantization after FFT processing was occurred in the delay compensation experiment. We confirmed that this problem was caused by valid bit-expression of the re-quantized data. To solve this problem, the novel method will be applied to VCS main product. The effectiveness of VCS trial product has been verified through the preliminary experimental results, but the overflow problem was occurred.

• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.205-212
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• 2006

In this paper, the numerical methods of searching the optimal position of optical phase conjugator (OPC) and the optimal dispersion coefficients of fiber sections are proposed, which are able to effectively compensate overall channels in $8{\times}40$ Gbps WDM system with non zero - dispersion shifted fiber (NZ-DSF) as an optical fiber. And the compensation characteristics in the system with two induced optimal parameters are compared with those in the system with the currently used mid-span spectral inversion (MSSI) in order to verify the availability of the proposed methods. It is confirmed that the compensation extents of the distorted 8-channel signals are improved within 2 dB power penalty by applying the induced optimal parameters into WDM system. It is also confirmed that two optimal parameters less related with the searching procedure of these optimal values, only if these depend on each other.

• Journal of Advanced Navigation Technology
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• v.27 no.4
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• pp.457-462
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• 2023

We proposed a flexible link configuration in a system combining mid-span spectral inversion (MSSI) and dispersion management used for long-distance transmission of high-capacity optical signals such as wavelength division multiplexing signals, and examined specific methods to increase chromatic dispersion and nonlinear distortion compensation effects. The dispersion map proposed to increase the flexibility of dispersion-managed link configuration has a 'random-inverse' structure. That is, in the proposed dispersion map, the residual dispersion per span (RDPS) of each fiber span in the first half section up to the optical phase conjugator is randomly distributed, and the RDPS distribution in the second half section reverses the distribution pattern of the first section. Although the proposed dispersion map has a random distribution of RDPS, it was confirmed that the distortion compensation effect is improved due to the fact that the dispersion profile is symmetrical with respect to the optical phase conjugator. In the dispersion map of the 'random-inverse' configuration, it was also confirmed that the compensation effect of the distorted wavelength division multiplexing signal becomes improved when the magnitude of the RDPS allocated to each fiber span is large.

• The Journal of the Acoustical Society of Korea
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• v.24 no.7
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• pp.416-422
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• 2005

Speech recognition in digital communication systems has very low performance due to the spectral distortion caused by speech codecs. In this paper, the spectral distortion by speech codecs is analyzed and a pre-processing method which compensates for the spectral distortion is proposed for performance enhancement of speech recognition. Three standard speech codecs. IS-127 EVRC. ITU G.729 CS-ACELP and IS-96 QCELP. are considered for algorithm development and evaluation, and a single method which can be applied commonly to all codecs is developed. The performance of the proposed method is evaluated for three codecs, and by using the speech features extracted from the compensated spectrum. the recognition rate is improved by the maximum of $15.6\%$ compared with that using the degraded speech features.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.6 s.109
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• pp.546-555
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• 2006

In this paper, the numerical methods of finding the optimal position of optical phase conjugator(OPC) and the optimal fiber dispersions are proposed, which are able to effectively compensate overall channels in $8{\times}40$ Gbps WDM system with non zero-dispersion shifted fiber(NZ-DSF) as an optical fiber. And the compensation characteristics in the system with two induced optimal parameters are compared with those in the system with mid-span spectral inversion (MSSI) technique in order to confirm the availability of the proposed methods. It is confirmed that the optimal parameter values induced in this approach are very useful to effectively compensate overall channels in WDM system with OPC. And, it is confirmed that two optimal parameters depend on each other, but less related with the searching procedure. The methods proposed in this research will be expected to alternate with the method of making a symmetrical distribution of power and local dispersion in real optical link which is a serious problem of applying the OPC into multi-channels WDM system.

• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.462-467
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• 2016

Dispersion management (DM) combining with mid-spans spectral inversion (MSSI) is one of the various techniques compensating for the distorted optical signals. For the flexible implementation of this configured link, the compensation characteristics in the optical link with artificial distribution of the gradually ascending and descending of single mode fiber (SMF)'s lengths and residual dispersion per span (RDPS) as the number of fiber spans are assessed as a function of the control positions of net residual dispersion (NRD). It is confirmed that the best compensation is obtained by distributing gradually ascending or descending of SMF's lengths and RDPS capable to place NRD control position at fiber span, in which optical pulse width is most narrow.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.49 no.4
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• pp.9-17
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• 2012

In this paper, we show the memory effect of the high-power amplifiers for wied-band signals, present a compensation method for the nonlinearity combined with memory effect, and analyze its performance. For the modeling and the compensation of the nonlinear high-power amplifier with memory effect, we investigate the Volterra series model, the Wiener model, and the Hammerstein model. As a compensator scheme, we propose a digital feedforward technique. Compared to analog feed-forward scheme, the proposed scheme has better stability and adaptability to the environmental changes. It has a simpler structure than the conventional digital nonlinear compensation schemes. The result of computer simulations using ADS of the Agilent shows that spectral re-growth is suppressed by more than 20 dB, which amounts to at least 10 dB back-off. Considering the compensation performance, implementation complexity, and convergence rate, we could conclude the Wiener model is most suitable for the proposed scheme.

• Journal of Biosystems Engineering
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• v.22 no.3
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• pp.269-278
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• 1997

An automatic level measurement system was developed to level the land fer direct seeding of rice. A laser transmitter/receiver set was used to measure land-level. The inclination error occurred in level measurement on irregular land surface could be compensated by attaching rotating mass. The level measuring experiments were performed on three kinds of different shapes(step, random, sine). This system could accurately measure step level of which amplitude was 40mm in 0.5s, random level change within $\pm$ 5mm maximum measurement error, and sine level change of which spatial frequency was 0.5m-1. To verify performance of the inclination error compensation system, frequency transfer function(acceleration input vs. inclination error) was computed by spectral analysis. The inclination error was decreased about 20㏈ by error compensation system.

• MALSORI
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• no.53
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• pp.157-169
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• 2005

This paper proposes an efficiently representing method of spatial cues on multichannel spatial audio coding. The Binaural Cue Coding (BCC) method introduced recently represents multichannel audio signals by means of Inter Channel Level Difference (ICLD) or Source Index (SI). We tried to express more efficiently ICLD and SI information based on Inter Channel Correlation in this paper. We adopt different spatial cues according to ICC and propose a compensation method of empty spectrums created by using SI. We performed a MOS test and measuring spectral distortion. The results show that the proposed method can reduce the bitrate of side information without large degradation of the audio quality.

• Journal of the Optical Society of Korea
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• v.3 no.2
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• pp.35-40
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• 1999

One of main error sources in white light scanning interferometry is the inaccuracy of scanning mechanisms in that PZT(piezoelectric transducer) micro-actuators are preferably used. We propose a new calibration method that is capable of identifying actual scanning errors directly by analyzing the spectral distribution of sampled interferograms. This calibration provides an effective means of self-compensation for the non-linearity errors caused by PZT hysteresis, enhancing the measurement uncertainty to a level of 5 nanometers over an entire measuring range of 100 ${\mu}{\textrm}{m}$.