• Proceedings of the KIPE Conference
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• 2018.07a
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• pp.162-164
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• 2018

스위칭 주파수의 대역 확산 (Spread Spectrum) 기법은 전력 변환 장치의 전자 방해 잡음 (Electromagnetic Interference; EMI)를 줄일 수 있다. 하지만 공진형 컨버터는 스위칭 주파수 가변을 통해 출력 전압을 제어하기 때문에 스위칭 주파수의 대역 확산 기법을 적용하게 되면 출력 전압이 크게 흔들리게 된다. 본 논문은 LLC 공진형 컨버터에 대역 확산 기법을 사용함과 동시에 확산된 스위칭 주파수 대역의 위상 제어를 통해 출력 전압을 제어하는 방법을 제시하고자 한다. 제안하는 출력 전압 제어 성능 향상 및 전자방해잡음 감소 성능은 500 W 프로토타입 컨버터를 사용하여 검증하고자 한다.

• Journal of Navigation and Port Research
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• v.35 no.8
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• pp.643-647
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• 2011

In this paper, we study the application of DSSS(Direct Sequence Spread Spectrum) in underwater acoustic communication for robust the ISI(Inter-Symbol Interference. We confirm the application of DSSS in underwater acoustic communication in underwater by the simulation with underwater channel impulse response and experiment. As a simulation result, the BER of QPSK technique is $1.14{\times}10^{-1}$ and the BER of DSSS technique is $6.73{\times}10^{-3}$. And we performed the experiment of DSSS technique in underwater. As a experiment result, the BER of QPSK technique is $3.19{\times}10^{-1}$ and the BER of DSSS technique is $5.17{\times}10^{-4}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.18 no.2
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• pp.218-230
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• 1993

A power line modem(PLM) which transfers data safely through power lines in houses or small offices is considered. When a power line is used for communications, transmitted signals could be affected by the channel characteristics such as frequency-selective fading, interference, and time-varying attenuation. In order to overcome these impairments, a direct sequence(DS) technique which is well known as an effective instrument against a variety of interferences and hostile channel properties is employed. Using a DS technique, however, requires more circuits such as PN code generator circuits, code modification circuits, and complicated synchronization circuits, and it also results in substantial acquisition delay. In this paper, some of these circuits are implemented via software programmed in the system controller, and the complicated synchronization circuits are replaced by simple circuits utilizing a 60 Hz power signal for synchronization. The synchronization ciruits used in this paper virtually eliminate the substantial acquisition delay, and is also designed to free influence of 60 Hz zero crossing jitters which reside in a power signal. As a result, a PLM using a DS technique is realized in the form of wall-socket plug, and the PLM hardware would be very much simplified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.2
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• pp.182-188
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• 2018

In order to increase the robustness of the uplink for UAS(Unmanned Aerial System), we propose a jamming signal rejection algorithm. In the UAS datalink system, DSSS (direct sequence spread spectrum) is used to reduce the radio noise or jamming signal. In general, jamming signals below the spreading gain are recoverable but the signals beyond the spreading gain can not be recovered. In this paper, these jamming signals beyond spreading gain are detected using the threshold detector in the spectrum area then, generate the estimated signals from the sine wave generator. Finally, we obtain the desired signal to remove jamming signals from the received signals. The proposed scheme can eliminate jamming signals while minimizing the hardware complexity and the original signal loss.

• Aerospace Engineering and Technology
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• v.8 no.1
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• pp.179-186
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• 2009

This paper describes the design and implementation for spread spectrum FTS encoder and decoder. The FTS command format is defined by 64 bit encrypted packet that contains all required information relayed between the ground and the vehicle. Encryption is accomplished using the Tripple-DES encryption algorithm in block encryption form. The proposed FTS encoder and decoder is using the Convolution Encoding and Viterbi Decoding for forward error correction. The Spread Spectrum Modulation is done using a PN code, which is 256 bit gold code. The simulation result shows that the designed FTS decoder is compatible with the designed FTS encoder.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.8
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• pp.1422-1430
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• 2016

Researches for oceans are limited to military purpose such as underwater sound detection and tracking system. Underwater acoustic communications with low-probability-of-interception (LPI) covert characteristics were received much attention recently. Covert communications are conducted at a low received signal-to-noise ratio to prevent interception or detection by an eavesdropper. This paper proposed optimal covert communication model based on direct sequence spread spectrum for underwater environments. Spread spectrum signals may be used for data transmission on underwater acoustic channels to achieve reliable transmission by suppressing the detrimental effect of interference and self-interference due to jamming and multipath propagation. The characteristics of the underwater acoustic channel present special problems in the design of covert communication systems. To improve performance and probability of interception, we applied BCJR(Bahl, Cocke, Jelinek, Raviv) decoding method and the direct sequence spread spectrum technology in low SNR. Also, we compared the performance between conventional model and proposed model based on turbo equalization by simulation and lake experiment.

• The Journal of the Acoustical Society of Korea
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• v.31 no.7
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• pp.441-448
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• 2012

Spread spectrum provides the minimized inter-symbol interference, the low probability of intercept and the multiple access capability. This paper presents a direct sequence spread spectrum with carrier/timing recovery and equalizer which compensates the delay spread caused by multipath transmission. When the sea trials were performed in Korean East Sea, the bit error rates of QPSK and direct sequence spread spectrum are $1.46{\times}10^{-2}$ and $5.17{\times}10^{-4}$ at 3 km source-receiver range, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.12
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• pp.1700-1706
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• 2016

To improve the number of simultaneous transmissions of machine-to-machine traffic in a spread spectrum ALOHA channel, we propose a new spreading technique called doubly truncated cyclic code shift keying (DTCCSK). By truncating the codeset of cyclic code shift keying, DTCCSK freely adjusts the spreading factor and the symbol length. As a result, DTCCSK exhibits both a high spectral efficiency of M-ary signaling and low implementation complexity of a direct sequence.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.350-351
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• 2012

본 논문에서는 ATSC 지상파 DTV시스템에서 계층변조를 사용하여 재난 방송용 부가 데이터를 전송하는 기법을 제안한다. ATSC 지상파 DTV시스템에서 계층변조를 사용하는 방식으로는 ADT(Augmented Data Transmission) 방식과 대역확산방식이 있다. ADT방식은 상대적으로 높은 데이터 전송율을 가지지만 신호가 도달할 수 있는 커버리지가 좁은 반면 대역확산방식은 낮은 데이터 전송률을 가지지만 신호가 도달할 수 있는 커버리지가 넓은 장점이 있다. 따라서, 재난 발생시 넓은 커버리지에 신속하게 긴급경보 방송을 송신하기 위해서는 대역확산기반의 계층변조 방식이 유리하다. 본 논문에서는 ATSC 지상파 DTV시스템에서 긴급경보 방송을 위해 대역확산기반의 계층변조 방식을 사용한 경우 전송용량 및 전계강도와 도달할 수 있는 전송 거리를 분석한다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.6A
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• pp.586-592
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• 2006

In this paper, a novel detection method called the joint multiple frequency cell (JMFC) detection is addressed for spread spectrum code acquisition in the presence of residual Doppler frequency offset (RDFO). When the RDFO exists, the correlation peak used for detection during the acquisition process is split into several lower neighboring peaks, resulting in severe degradation in the detection performance, and consequently, in the overall acquisition performance. In the JMFC detection, a decision variable for detection is formed by combining several consecutive correlator outputs, so that the reduction in the correlation value due to the RDFO can be alleviated. Numerical results show that the proposed scheme can offer better detection performance over the conventional scheme based on the cell-by-cell detection.