• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.3B
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• pp.196-201
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• 2002

OFDM(orthogonal Frequency Division Multiplex) modulates transmitting data with many carriers in parallel. As a result, high-speed data transmission is carried out and high spectral efficiency is provided by overlapping orthogonal frequencies. Therefore, OFDM is applied to many communication systems. In this paper, according to modulation methods(M-PSK and M-QAM), coded-OFDM wireless communication is simulated. Turbo code is used and two channels(virtual and real channel) are used. both channels have multipath delay spread, Gaussian noise, and peak power clipping. As a result of the simulation, coding gain is about 3dB and it is proved that M-QAM modulation is better than M-PSK. Start after striking space key 2 times.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.9
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• pp.738-745
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• 2012

This paper proposes an approximated soft decision demapping algorithm with low computational complexity for coded 4+12+16 amplitude phase shift keying (APSK) in an additive white Gaussian noise (AWGN) channel. To derive the proposed algorithm, we approximate the decision boundaries for 4+12+16 APSK symbols, and then decide the log likelihood ratio (LLR) value for each bit from the approximated decision boundaries. Although the proposed algorithm shows about 0.6~1.1dB degradation on the error performance compared with the conventional max-log algorithm, it gives a significant result in terms of the computational complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.12
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• pp.1366-1381
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• 1991

The error rate equation of QPSK signal received through m-distribution fading channel in tone interference and Gaussian noise environments has been derived and evaluated numerically to be shown in figures. The derivation has been done for two cases. The one case is that only the signal is under the influence of fading and the another case is that signal and interference are under the influence of fading simultaneously. The evaluated results show that the error that performance when fading influences signal and interference simultaneously is worse than that when fading influence signal only. Also the results show that a late amount of improvement can be gained by direct sequence spread spectrum system and the amount of improvement becomes small as the influence of interference and fading becomes small.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.1
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• pp.51-59
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• 2004

We design multilevel coding(MLC) with a semi bit-interleaved coded modulation(BICM) scheme based on low density parity check(LDPC) codes. Different from traditional designs, we joint the MLC and BICM together by using the Gray mapping, which can transmit the multimedia data over several equivalent channels with different code rates. To get a good performance from signal-to-noise ratio(SNR) very close to the capacity of the additive white Gaussian noise(AWGN) channel, random regular LDPC code and a simple semi-algebra LDPC(SA-LDPC) code are discussed in MLC with parallel independent decoding(PID). Finally, the numerical results demonstrate that the proposed scheme could achieve both power and bandwidth efficiency for multimedia communication system.

• Journal of Broadcast Engineering
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• v.8 no.2
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• pp.109-115
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• 2003

In this paper we propose an efficient method to broadcast digital television signals using Single Frequency Networks (SFNs) in the Advanced Television Systems Committee (ATSC) transmission systems. Since the proposed schemes to synchronize multiple transmitters minimize the changes from the conventional ATSC system, the hardware complexity for the changes is very low. Our simulation results show that the proposed scheme makes less than 0.1 dB degradation at the threshold of visibility (TOV： BER= 3$\times$$10^{-6}$) in the additive white Gaussian noise (AWGN) channel. It is possible to reduce the performance degradation by increasing an initialization period of the proposed scheme.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.12
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• pp.1804-1809
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• 2017

A data acquisition (DAQ) system based on oscilloscope was developed and evaluated for radiation detector. The dedicated LabVIEW program that perform the oscilloscope control and the data process was developed. Triggered events for each analog channel were acquired and the output signals were subsequently digitized and recorded for offline processing. Radiation pulse generation circuit was developed to evaluate the intrinsic characteristics of DAQ system. Energy linearity and energy resolution performances were assessed by voltage-peak channels and FWHM obtained from Gaussian fit, respectively. Radiation detector consists of LYSO and GAPD array. The 16 output signals were multiplexed by the RCD networks, and they were fed into the custom-made preamplifiers. Voltage-peak channels was linearly changed as a function of input voltage and the estimated coefficient of determination ($R^2$) was 0.999. No considerable changes in voltage resolution were observed. All 16 crystals were clearly identifiable on the resulting flood image and the mean energy resolution was ~15.1%. This study demonstrated that it is feasible to develop the DAQ system based on oscilloscope and LabVIEW program for radiation detector and the proposed approach offers opportunities to build simple DAQ system in various radiation measurement field.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1247-1249
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• 1993

In this paper, NUDFET(NonUniformly Doped Field Effect Transistor) is presented as an alternative which offers the possibility of reducing the power necessary to operate switching circuits without a substantial loss in speed. The purpose of this NUDFET is to modify the electric field profile in order to cause carrier velocity saturation to occur at a lower voltage than it would occur in the uniformly doped device of the same channel length. The more MESFET and NUDFET circuits are realized, the more accurate model ins the performance of these devices become required. Analytic model ins was replaced by numerical analysis because of the complexity of device configuration. In this paper, FEM is selected because of simpler local mesh refinement and smaller computer memory than FDM. For accurate analysis, this paper has applied the Scharfetter-Gummel(S-G) Scheme and seven-point Gaussian Quadrature rule to assembly of the finite-element stiffness matrices and right-hand side vector of the semiconductor equations.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.685-688
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• 2003

In this paper, a performance comparison between two blind signal estimation algorithms in a LTI channel is considered. The two algorithms, Iterative Least-Squares with Projection (ILSP) and a modified ILSP, are based on the finite-alphabet property of input symbols. This case typically arises in a multiple access system with a sensor array antenna at the receiving end. We start with the formulation of a maximum-likelihood (ML) estimation problem under an additive white Gaussian noise assumption. A blind ML estimator is derived with its iterative algorithm for calculation. Then we narrow down the consideration of this problem to QPSK case so that a modified algorithm is proposed for $\pi$/4-QPSK case. The modified version is compared with the original ILSP algorithm in terms of the rate of the convergence to global minima. A computer simulation shows that the modified algorithm gives a better performance. This result implies that the performance of the blind separation algorithms may be greatly improved by adopting a smart coding scheme with rich structure.

• Korean Journal of Optics and Photonics
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• v.22 no.3
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• pp.122-128
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• 2011

The AWG-filtering effect was investigated on a bidirectional 100-GHz-channel-spacing WDM-PON link using spectrum-sliced and RSOA-amplified light sources for downstream signals and a wavelength reuse technique for upstream signals. Signal performances of three different filtering AWGs, including Gaussian, trapezoidal, and rectangular types, were compared on link transmission with fiber nonlinear effects. As an extinction ratio of a downstream signal varied, the effect for both directional signals was analyzed and optimized. It was found that there was an optimal pass bandwidth of an AWG for the balance between relative intensity noise decrement and cross phase modulation noise increment as the bandwidth got wider.

• Journal of Broadcast Engineering
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• v.19 no.6
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• pp.767-788
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• 2014

The worldwide transition from analog to digital broadcasting has now been completed and the need to study next generation standards for Ultra High Definition TV (UHDTV) broadcasting, and broadcasting & communication convergence systems is rapidly growing. In particular, high resolution mobile broadcasting services are needed to satisfy recent consumers. Therefore, the development of highly efficient convergence broadcasting systems that provide fixed/mobile broadcasting through a single channel is needed. In this paper, a service scenario and requirements for providing 4K UHD & HD convergence broadcasting services through a terrestrial single channel are analyzed by employing the latest transmission and A/V codec technologies. Optimized transmission parameters for 6 MHz & 8 MHz terrestrial bandwidths are drawn, and receiving performances are measured under Additive White Gaussian Noise (AWGN) and time-varying multipath channels. From the results, in a 6 MHz bandwidth, the reliable receiving of HD layer data can be achieved when the receiver velocity is maximum 140 Km/h and is not achieved when the velocity is over 140 Km/h due to the limit of bandwidth. When the bandwidth is extended to 8 MHz, the reliable receiving of both 4K UHD and HD layer data is achieved under a very fast fading multipath channel.