• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.9
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• pp.11-23
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• 2000

Multicarrier DS-CDMA is an effective approach to realize wideband CDMA system in a multipath fading channel. In this paper, we propose a convolutionally-coded overlapped multicarrier DS-CDMA system, and analyze the performance with subband overlapping variation to determine the overlapping percentage showing best performance. Given a total number of subcarriers M*R, we will show that the BER variation is highly dependent on the rolloff factor P of raised-cosine chip wave-shaping filter irrespective of convolutional encoding rate I/M and repetition coding rate 1/R. We also analyze the possibility of reduction in total MUI by considering both variation of a rolloff factor (0 ($\beta$ :1) and variation of subband overlapping factor (0 ( A :2), and show that the proposed system may outperform the multicarrier DS-CDMA system in [1, 12].

• Journal of the Korea Society of Computer and Information
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• v.9 no.2
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• pp.97-104
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• 2004

As a channel of a DS-CDMA system is shared among several users, the receivers face the problem of MAI. Also the bandlimited channel leads to ISI. Both components are undesired, but unlike the additive noise process, which is usually completely unpredictable, their space-time structure helps to estimate and remove them. This paper investigates a DS-CDMA system with a fading multipath channel. The investigations have been separated into a channel estimation part and a reception part. In the estimation part of seperated two parts, the multipath parameters such as DOA and TOA are evaluated in this paper. In the part of receiver. we used these parameters and tested the performance of this receiver about space-time beamformers. To assess many different estimation techniques and beamformers, the simulation compared with theoretical values is performed.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.4
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• pp.160-164
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• 2004

In DS/CDMA(direct sequence code division multiple access) system using the approximated analytic chip waveforms are applied. Proposed chip waveforms are classified into 2 types: uniform chip waveforms with uniform envelope and non-uniform chip waveforms with non-uniform envelope. It has confirmed that the similarity of the approximated analytical chip waveforms is compared using chip waveforms, envelope, phase, correlation, and bandwidth properties.

• Journal of the Korea Computer Industry Society
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• v.3 no.7
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• pp.937-942
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• 2002

In this paper, using diversity the DS-CDMA system to modulation, performance of DS/CDMA system we have been analyzed. Channels is multipath resolution, and receiver is assemed maximal ratio combining(MRC) using to rake receiver. Simulations have been using element number of communication channels. Therefore, progress average bit error probability have been element number of increment.

• Proceedings of the IEEK Conference
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• 2000.06a
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• pp.77-80
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• 2000

In this paper, we implemented the voice modem using the multicarrier DS-CDMA in powerline channels. Both TMS320C5402 of Texas Instrument and FPGA FLEX 10K EPF10K100ARC240 of ALTERA are used to realize the proposed system. For robustness in the powerline channel, we used multicarrier DS-CDMA modulation, convolutional encoding/Viterbi decoding, and interleaving. Finally, we showed satisfactory performance in the laboratory experiment.

• Proceedings of the IEEK Conference
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• 2000.11a
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• pp.461-464
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• 2000

본 논문에서는 위성통신 환경에서 DS/CDMA DPSK 시스템의 성능을 분석한다. 성능분석의 척도로 비트오류확률을 사용한다. 위성전송로는 쉐도잉이 있는 라이시안 페이딩 전송로로 모델링한다. 수치계산의 결과, 위상잡음이 존재할 때 비트오율 성능이 저하되므로 시스템 용랑이 감소될 것이 예상된다. 또한 위성전송로에서는 쉐도잉이 시스템 전체 성능에 커다란 영향을 미침을 알 수 있다. 본 논문에서의 분석은 DS/CDMA 기반의 위성통신 시스템 설계에 적용할 수 있다.

• The Journal of the Acoustical Society of Korea
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• v.17 no.6
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• pp.29-36
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• 1998

본 논문은 확산된 데이터에 반송파를 1개가 아닌 여러 개의 반송파로 변조하는 MC DS-CDMA 시스템을 적용하여 페이딩 요소를 고려하지 않는 채널, 즉 Gaussian 채널에서 다중 사용자 간섭 및 부분대역 재머, 최악의 부분대역 재머 간섭하에서 성능을 분석하여 단 일 반송파를 사용한 기존의 DS-CDMA 시스템과 비교 분석한다. 또한, Gaussian채널에서 고려된 간섭들에 대해 다중경로 페이딩 채널에서 시스템 성능을 분석하고 Gaussian채널에 서 분석된 시스템 성능과 비교한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.373-377
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• 2006

본 논문에서는 이동위성통신 DS/CDMA 시스템의 상향링크 채널에 대한 이중모드 통신방식을 제안하고, 제안 시스템의 성능을 해석하고 제안 시스템의 유용성도 확인하였다. 또한 이동위성통신 DS/CDMA 시스템에 큰 도플러 옵셋의 해결방안으로 Kajiwara가 제안한 이중채널 방식을 이용하여 이동위성채널에 널리 쓰이는 라이시안 페이딩 모델을 설정하였으며 변조 방식으로는 DCPSK 신호를 이동체의 속도와 전송률 에러의 성능을 비교 분석하였다.

• ETRI Journal
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• v.28 no.5
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• pp.684-687
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• 2006

In this letter, we evaluate the system performance of a space-time block coded (STBC) multicarrier (MC) DS-CDMA system over a time selective fading channel, with imperfect channel knowledge. The average bit error rate impairment due to imperfect channel information is investigated by taking into account the effect of the STBC position. We consider two schemes: STBC after spreading and STBC before spreading in the MC DS-CDMA system. In the scheme with STBC after spreading, STBC is performed at the chip level; in the scheme with STBC before spreading, STBC is performed at the symbol level. We found that these two schemes have various channel estimation errors, and that the system with STBC before spreading is more sensitive to channel estimation than the system with STBC after spreading. Furthermore, derived results prove that a high spreading factor (SF) in the MC DS-CDMA system with STBC before spreading leads to high channel estimation error, whereas for a system with STBC after spreading this statement is not true.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.5
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• pp.1-13
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• 1995

In this paper, we evaluated the mean acquisition time and it's variance of the rapid synchronization system using the DMF(Digital Matched Filter) under the DS/CDMA system which uses the long period PN code. And we implemented the synchronization system that satisfies the specification demanded by the proposed EIA/TIA Interim Standard of Qualcomm Company. We showed that the state of the PN spreading code was estimated using the DMF(Digital Matched Filter) and then exact and fast chip synchronization could be achieved by the early-late tracking loop in the multiple channel environment. And we suggested the possibility that this synchronization system could be useful in the emerging digital cellular DS/CDMA system.