• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.8
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• pp.43-53
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• 2001

Wavelength conversion devices are essential to build an expanding all-optical network, and various types of wavelength conversion techniques are being researched. Among them, wavelength conversion based on the cross phase modulation in a directionally coupled semiconductor optical amplifier has been introduced and the concept has been experimentally proved. In this paper, a split-step method is applied to properly model the mentioned wavelength converter in the time-domain and various characteristics have been analyzed. It is shown that the present modeling approach can explain the results of the reported experimental results. Furthermore the wavelength conversion is shown to be well performed when the input signal wave and the converted wave travels in the opposite direction. The simulation shows that the positive and negative chirping appear simultaneously at both the leading and trailing of edges of the optical pulse.

• Journal of Advanced Navigation Technology
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• v.11 no.1
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• pp.9-16
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• 2007

In this paper, the Bit Error Ratio (BER) performances of the D8PSK modulation schemes for VDL Mode-2 are analyzed according to the matched and unmatched cases of the channel filters. The carrier frequency and phase offset effects are analyzed with unmatched case. Generally in digital transmission techniques, the Root Raised Cosine filters which are used as channel filters are applied to both sides at transmitter and receiver in order to achieve no ISI, but in VDL Mode-2, the Raised Cosine Filter is used only in transmission section and the receiver section uses general low pass filter, therefore we could not achieve ISI reduction effects but can have better spectrum quality. From the simulation results, the error probability is increased slightly (1~2dB) with use of un-matched channel filter, we got the conclusions that carrier phase offset do not effect to bit error ratio, but the frequency offset effect is so serious. Finally, narrow band D8PSK modulation signals are generated by the use of Digital Up-Converter and then its features are compared with analog modulator.

• Journal of Broadcast Engineering
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• v.12 no.2
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• pp.120-127
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• 2007

In this paper, we describe a new 1/4 rate robust modulation techniques for Enhanced-x VSB system which is fully backward compatible with ATSC 8-VSB standard. 1/4 rate mode Enhanced-xVSB system provides broadcasters with a wide choice of trade-offs of data rate vs amount of robustness of enhanced data for pedestrian/mobile services. Lab test results of proposed Enhanced-x VSB 1/4 rate mode robust stream are a significantly improved multipath as well as AWGN reception performance for Enhanced-x VSB receiver. We suggest an Enhanced-x VSB terrestrial broadcasting system for ATSC HDTV and pedestrian/portable TV simultaneous broadcasting service providing.

• Journal of Advanced Navigation Technology
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• v.7 no.2
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• pp.141-148
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• 2003

This paper presents and compares several techniques that detect the symbol rate of unknown received signal. Symbol rate is detected from the power spectral density of the circuits such as the delay and multiplier circuit, the square law circuit, and analytic signal, etc. As a result of discrete Fourier transform of the output signals of these circuits, a lot of spectral lines and some peaks appear in frequency domain and the position of first peak is corresponding to the symbol rate. If a spectral line on the frequency that is not located in symbol rate is larger than the first peak, the symbol rate is erroneously detected. Thus, the ratio between the value of first peak and the highest side spectral line is used for the measure of the performance of symbol rate detector. For the MPSK modulation, the analytic signal method shows better performance than the delay and multiplier and square law circuits when the received signal power is lager than -20dB. It is also noted that the delay and multiplier circuit is not able to detect the symbol rate for the QAM modulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.4
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• pp.535-543
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• 2002

In this paper, we propose $\pi$/8 shift 8PSK and trellis-coded $\pi$/8 shift 8PSK-OFDM techniques by applying $\pi$/4 shift QPSK to trellis-coded modulation (TCM), and performing signal set expansion and set partition correspondingly based on phase difference. In our Viterbi decoding algorithm, up to L phase differences from successively received symbols are employed in the new branch metrics. Such sliding multiple symbol detection (SMSD) method provides improved bit-error-rate (BER) performance in the differential detection of the trellis-coded $\pi$/8 shift 8PSK-OFDM signals. The performance improvements are achieved for different communication channels without sacrificing bandwidth and power efficiency. It thus makes the proposed modulation and sliding detection scheme more attractive for power and band-limited systems.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.1
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• pp.53-58
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• 2017

UFMC is known as the one among novel multi-carrier modulation techniques which are designed for replacing OFDM for 5G wireless communication systems. It is the generalized model of OFDM and FBMC, which combines the advantages of OFDM and FBMC and avoids their weak points. UFMC is more robust in synchronization condition like Time-frequency misalignment compared to CP-OFDM. Moreover UFMC is more proper to burst uplink transmission like M2M 5G Communications. In this paper we analyze the BER performance in various channels and speeds. The simulation result shows that the BER performance is lowered when mobile devices are moving fast and the BER performance is so sensitive for the good channel environment.

• Journal of Navigation and Port Research
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• v.34 no.10
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• pp.769-774
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• 2010

The performance of underwater communication system is influenced on channel characteristic. Delay spread cause by reverberation and multi-path happen the ISI (Inter Symbol Interference) and reduces the communication performance. In this paper, we analyze the performance of acoustic communication experiment in underwater to use the OFDM (Orthogonal Frequency Division Multiplexing) technique for overcome the reverberation and multi-path. As a result, we acquired the BER of modulation techniques. The BER of 2kbps data rate is $1.22{\times}10^{-1}$ and BER of 4 kbps data rate is $2.47{\times}10^{-2}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.5A
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• pp.440-446
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• 2010

Convergence of IT and BT is considered in many area, especially in medical care industry. The example of this trend is a capsule endoscope. But in a capsule endoscope, communication through human body has a few restrictions. At first, the transmit power should be limited not to have a bad effect on human organs and for the battery capacity. Second, the channel characteristic of human body has not been examined exactly. Third, general modulation / demodulation techniques which require a channel estimation cannot be used because of battery limit. There also may be a lot of interference signals because a capsule endoscope uses UWB bandwidth. In this paper, we introduce Chirp Spread Spectrum Differential Binary Phase Shift Keying(CSS-DBPSK) and propose Chirp Spread Spectrum On-Off Keying(CSS-OOK) which don't require a channel estimation and robust to interference signals. Using CSS-DBPSK or CSS-OOK, we can get 5 dB or 2~3 dB of Eb/N0 gain at 10-5 target BER. And if there are interference signals, those gains of CSS-DBPSK and CSS-OOK are increased.

• Journal of the Korean Society for Railway
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• v.20 no.4
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• pp.448-457
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• 2017

In this paper, for high speed railway propulsion systems, a single phase PWM Converter using discontinuous PWM (DPWM) was investigated. The conventional PWM Converter uses a low frequency modulation index of less than 10 to reduce switching losses due to high power characteristics, which results in low control frequency bandwidth and requires an additional compensation method. To solve these problems, the DPWM method, which is commonly used in three phase PWM Inverters, was adopted to a single phase PWM Converter. The proposed method was easily implemented using offset voltage techniques. Method can improve the control performance by doubling the frequency modulation index for the same switching loss, and can also bring the same dynamic characteristics among switches. Proposed DPWM method was verified by simulation of 100 kW PWM converter.

• 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.