• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.11A
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• pp.1613-1619
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• 2000

이 논문에서는 전파재널 측정 시스템을 이용하여 건물내 무선 채널의 전파특성인 실효 시간지연 확산과 경로손실을 측정하고 분석한 결과를 제시한다. 구성된 측정 시스템은 미끄럼 상관기를 이용한 대역확산 채널 측정 시스템에서 2 GHz에서 동작하며 3 m 의 분해능을 갖는다. 건물내 무선 채널 특성의 측정환경은 송신 안테나와 수신 안테나가 같은 층에 있을때, 서로 다른 층에 있을때, 그리고 사무실 안에 같이 위치할 때의환경으로구분하여 실험한다.

• 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 Korean Institute of Communications and Information Sciences
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• v.17 no.11
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• pp.1271-1278
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• 1992

In this paper, a practical model for evaluating and comparing the bit error rates(BERs) due to adjacent channel mutual interference in a synchronous and asynchronous frequency hopped spread spectrum multiple access(FH-SSMA) radio communication systems is proposed. After implementing the actual FH radio in both the sychronous and asynchronous case, the BER is computed and measured. An experiment of this system in mobile tactical environments reveals that the performance in the asynchronous case is lower than that of the synchronous case. The computer simulation model is an efficient tool for designing practical FH radios in mobile communication environments.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1993.10a
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• pp.617-619
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• 1993

• The Magazine of the IEIE
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• v.21 no.7
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• pp.43-51
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• 1994

본 논문에서는 최근 주목을 받고 있는 대역확산 통신방식을 이용한 무선LAN 시스템의 하드웨어 구현에 관해 논한다. 내용으로는 직접확산 (Direct Sequence Spread Spectrum (DS/SS)) 통신방식을 이용한 무선 LAN 전송부 구조, 디지탈 정합필터를 이용한 역확산 및 비동기 DS/SS 수신기 구조, DBPSK 및 DQPSK 변복조 방식, Timing 및 Clock 복원, 그리고 Carrier Sensing 방식등이 포함된다. 또한 실제 시스템 구현을 위해 필요한 몇가지 변수들에 대해서도 논한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.1
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• pp.539-542
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• 2005

In this paper, we propose a wireless data access system, which used direct sequence spread spectrum method and the ISM band with 900MHz radio frequency. By applying bi-directional transmission between wireless transmitter and receiver, it can be effectively connected with any kinds of RF-ID with 900MHz ISM band. Therefore it could economically be used as peripheral equipments for RF-ID system.

• Information and Communications Magazine
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• v.13 no.10
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• pp.76-85
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• 1996

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6A
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• pp.775-781
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• 1999

A multi-media variable processing gain DS/CDMA system are considered. Two types of information sources with different rates and transmitting powers are assumed to be stransmitted simultaneously in the same channel. Average signal-to-noise ratios at the correlation receiver outputs for each type of information sources are analytically derived as funtions of partial cross-correlations between spreading code sequences. As the difference of information rates between information sources increase, the difference between signal-to-noise ratio regarding random spreading code and that regarding pseudo random spreading code increases (maximum 1.3dB). The result can provide a analytical tools for use in multi-media DS/CDMA system design.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.2
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• pp.39-44
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• 2010

In this paper, we derive the channel capacity in order to transmit an additional data by using digital watermarking method in generalized-K fading channel. Spread spectrum watermarking is one of the digital watermarking methods which is the most promising technique due to it's very robustness to the channel noise and easy achieving of the signal detection by correlators at the receiver. It is important to analyze the channel capacity to transmit an additional data through wireless channel because the transmitted data would be affected by the channel fading effects. From the results, we confirm that the channel capacity of the SSW system can be determined by the HWR, WNR, PN length and host sampling frequency. Also, we verified that the level of HWR and WNR can be determined by the derived capacity formula. The results of this paper can be applied to general spread spectrum watermarking system.

• The Journal of the Acoustical Society of Korea
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• v.6 no.1
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• pp.5-14
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• 1987

In this paper, the transmission characteristics of a frequency-hopped spread spectrum communication system operating in the presence of both time and frequency-selective fading channel is presented. The receiver is a binary noncoherent matched-filter FFH-SS system with square-law combiner. The probability of error to the variations of the parameters such as signal-to-noise ratio, selectivity of a channel, and power ratio is derived with the use of diversity concept without considering the data rate. The analysis of the data for probability of error shoves that the performance of FFH-SS system in time-selective fading channel is better than in frequency-selective fading channel.