• Proceedings of the KIEE Conference
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• 2001.11c
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• pp.372-375
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• 2001

본 논문에서는 고속데이터 전송을 위한 CDMA 모뎀를 구현하였다. 데이터율 1Mbps의 트래픽 5채널에 직교부호를 곱하여 채널을 구분한 후 하나의 채널로 처리하였다. I,Q로 입력된 신호는 복소 곱셈기에서 칩 레이트 8Mcps로 OCQPSK(또는 HPSK) 변조하였다. 복조기는 I,Q의 신호를 역확산한 후 직교부호를 다시 곱하여 각 채널의 데이터를 분리한다. 변복조기의 구현은 클럭 속도 167MHz의 부동 소수점형 프로세서인 TI사의 TMS320C6701 DSP(Digital Signal Processor)를 사용하었고, long code 및 I,Q 채널 PN 코드는 IMT-2000 동기방식과 비동기방식의 규격에 정의된 2가지의 PN코드 발생기를 모두 구현하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.19 no.8
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• pp.1421-1432
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• 1994

The optimum design and performance of noncoherent TDL considering the effect of distortions due to the IF bandpasss filters are described. NRZ data and ideal filter is presumed in the simulation. The optimum filter bandwidth is calculated in the sense of minimizing the loop's squaring loss, which is equivalent to minimizing the loop's tracking jitter for a given data rate and data signal-to-noise ratio. As a result, the optimum filter bandwidth depends on the signal-to-noise ratio, and is obtained in the range of about 1-2 times of the data rate.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.5
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• pp.956-962
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• 2008

We propose the optical CDMA based audio acoustic sensor using optical fiber sensors which can be used in the bottom of the sea. In the proposed network, we analyzed the performance of noise power. Numerical simulations confirm that the performance can be improved by increasing the measuring time of optical sensors compared with using conventional WDMA method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.4 no.3
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• pp.517-526
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• 2000

In this paper, we propose the trellis coded spread spectrum communication system with one channel signal selection of the subset by the PN code. This paper proposes the Viterbi decoder that have the squared Euclidean distance of the order phase difference as well as 1st order phase difference as the branch metrics by using the multiple symbol detection method. TCM method was developed to overcome limited power and bandwidth efficiently in digital communication. we multiply one of convolution code's output data to PN code for applying TCM to the spread spectrum. We investigated the performance of the direct sequence/spread spectrum communication system with trellis coded modulation. In this system, we could improved the coding gain in the spread spectrum.

• Journal of IKEEE
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• v.12 no.2
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• pp.95-101
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• 2008

In this paper, we study an optimum design of search synchronization structure for Baseband Modem to support ISO/IEC 18185-5 and 24730-2 Standard. For DSSS Modem, we design the code acquisition and tracking structure which are important in receiver operation, and examine the parameters to be considered. The data and PN chip transmission rates and processing gain of the proposed modem are 59.7 kbps, 30.521875 Mcps, and 27 dB, respectively. This indicates that the noise immunity of the proposed modem is 17dB better than IEEE 802.11b (Processing gain : 10dB). Therefore, we design the optimum structure for the modem search synchronization which is compatible to the proposed modem standard.

• Proceedings of the Korea Multimedia Society Conference
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• 2003.11a
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• pp.9-12
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• 2003

웨이블릿 변환(Wavelet Transform)의 압축 방식 중 최근 압축률에서 뛰어난 성능을 보이는 MTWC 알고리즘의 특성을 이용하여 추출된 중요 계수에만 워터마크를 삽입하는 방법으로 디지털 영상에 시각적으로 보이지 않게 워터마크를 삽입하고, 워터마크된 영상과 PN(Pseudo Noise)code와의 계수차를 이용하여, 위터마크를 추출하는 통계학적 접근 방법을 제시하며, 워터마크가 삽입된 영상에 대한 다양한 공격(Attack)등에 대해서 기존의 방법들과 비교하여 효과적으로 워터마크를 추출할 수 있는 강인함을 실험을 통해 증명해 보였다.

• Proceedings of the Korean Institute of Communication Sciences Conference
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• 2004.07a
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• pp.471-471
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• 2004

• Proceedings of the Korea Society for Industrial Systems Conference
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• 1997.11a
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• pp.127-135
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• 1997

In this paper, we apply a digital modulation scheme called Multi-Carrier Code Division Multiple Access (MC-CDMA) in which data symbols are transmitted at multiple subcarriers. Each subcarrier is encoded with a phase offset of -π or π based on a pseudo-random noise(PN) sequence. MC-CDMA scheme is introduced to combat against the multipath fading. We annalize above system and derive the average probability of error in AWGN and Rayleigh fading environment.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.45-53
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• 2011

This paper is technical review about Direct Sequence Spread Spectrum(DSSS) to apply in launch vehicle system. First, we introduce communication protocol(carrier frequency, code length, process gain, data rate, chip rate etc) about several application system using DSSS. And then, we survey and summarize the effect of doppler shift to the DSSS. The doppler shift is important error factor for PN code tracking in the fast moving system like launch vehicle. So, spread spectrum code acquisition technique for a direct sequence system in the presence of doppler effect must be investigated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.10
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• pp.1968-1976
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• 2007

This paper proposes a hybrid pseudo-noise (PN) code acquisition scheme for Multicarrier Direct Sequence - Code Division Multiple Access (MC DS-CDMA) mobile communication systems on the code acquisition performance for Nakagami-m fading channel. The hybrid acquisition scheme combines parallel search with serial search to cover the whole uncertainty region of the input code phase. It has a much simpler acquisition hardware structure than the total parallel acquisition and can achieve the mean acquisition time (MAT) slightly inferior to that of the total parallel acquisition. The closed-form expressions of the detection and false-alarm probabilities are derived.