• Journal of Communications and Networks
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• 제7권1호
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• pp.13-20
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• 2005

In this paper, a new multi carrier, direct sequence code division multiple access (MC-DS-CDMA) system is proposed. Our new signal construction is based on convolutional encoding of the transmitted data, serial-to-parallel (S/P) conversion of the encoded data, Walsh-Hadamard-transformation (WHT), a second S/P conversion of the WHT outputs, spread spectrum (SS) modulation with a common pseudo-noise (PN) sequence, and then multicarrier transmission. The system bit error rate (BER) performance in frequency selective fading channel in the presence of additive white Gaussian noise (AWGN) and a jamming tone is analyzed and simulated. The numerical results are compared with those from an orthogonal MC-DS-CDMA system of Sourour and Nakagawa [7]. It is shown that the two systems have almost the same BER performance, but the proposed scheme has better anti-jamming ability.

• IEIE Transactions on Smart Processing and Computing
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• 제3권4호
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• pp.181-190
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• 2014

This paper reports a cognitive radio network architecture based on overloaded multicarrier direct sequence code division multiple access (O-MC-DS-CDMA). The O-MC-DSCDMA technique combines CDMA with a multicarrier modulation technique to overcome the channel fading effects. In this technique, secondary users are enabled to share the available bandwidth with the existing primary users. Two sets of orthogonal Gold codes are used to support the primary and secondary users simultaneously. The orthogonality between the spreading codes is lost due to the non-zero cross correlation between the codes and the timing synchronization error in the uplink transmission, which causes interference between primary and secondary users. This paper proposes two modified hybrid parallel/successive interference cancellation techniques for primary and secondary user base station receivers with multiple antennas to suppress the interference among users. Interference among the same group of users is cancelled by parallel interference cancellation and the interference among groups is cancelled using successive interference cancellation. The simulation results confirmed that the proposed modified interference cancellation techniques show better BER performance over conventional interference cancellation techniques.

• 한국항행학회논문지
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• 제12권2호
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• pp.115-121
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• 2008

본 논문에서는 DS-CDMA 시스템 구현 시 복잡성을 감소시키는 다중접속간섭 등의 여러 감쇠 요인을 고려하여 이를 개선시킬 수 있는 FS MC-CDMA 시스템의 성능을 분석하고 열악한 무선 모바일 환경에서 성능 개선기법인 BCH 부호화기법을 채용하여 FS MC-CDMA 시스템의 성능을 개선하였다. 또한 차세대 무선 모바일 통신 채널 환경으로는 나카가미 페이딩을 적용하여 FS MC-CDMA 시스템의 성능을 분석하여 검토하였다.

• 한국전자파학회논문지
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• 제10권7호
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• pp.1033-1043
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• 1999

We consider an improved multicarrier(MC) CDMA system that combines both DS-CDMA with a concatenated orthogonal/PN spreading sequence and MC modulation. This system incorporates the advantages of DS-CDMA with a concatenated sequence to achieve large user capacity and MC modulation technique to combat the effects of a multipath fading channel and intersymbol interference(ISI). Considering voice activity and imperfect sectorization, the system performance is analysed for the maximal ratio combiner(MRC) under a multicell, multiuser, and multipath Rayleigh/Rician fading channels. The performance of the system is improved much more for the single path fading channel compared to the multipath fading channel. Also the system is shown to have the more improved average bit error rate(BER) over the orthogonal MC-CDMA with the conventional PN sequence.

• 한국정보통신학회논문지
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• 제2권3호
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• pp.309-315
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• 1998

본 논문에서는 직접대역확산방식을 이용한 DS-CDMA의 ISI나 ICI와 같은 문제점을 다수의 협대역 부반송파를 이용하여 해결할 수 있도록 제안된 변조방식인 MC-CDMA시스템의 성능을 분석하였다. 여기서 고려한 채널모델은 Rician 페이딩 분포를 가지며, 부반송파에서의 페이딩은 서로 독립적인 특성을 갖는 옥내이동통신 환경으로 하였다. 시스템의 성능분석을 위해 먼저 오류정정부호를 사용하지 않은 시스템의정방향과 역방향의 비트오율을 분석하였다. 그리고 (7,4) Hamming 부호, (15,7) BCH 부호, 구속장이 7인 1/2-길쌈부호와 같은 오류정정부호를 사용하였을 때 이용자수와 부반송파수 그리고 신호대 잡음비(SNR)에 따른 비트오율변화를 분석하므로써 부호화 MC-CDMA 시스템의 성능을 분석하였다.

• 한국주조공학회지
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• 제33권5호
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• pp.193-203
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• 2013

The Ni-base superalloy CM247LC was directionally solidified (DS) using the Bridgman-type furnace to understand the effect of the chill plate on the microstructural evolution, such as dendrite arm spacing, microporosity, and MC-type carbide. The DS process was also modeled by the PROCAST to predict the solidification rate, thermal gradient, and resultant cooling rate in the entire length of the DS specimen. Due to the quenching effects of chill plate, four distinct areas were found to form in the specimen, in which the solidification rate was changed, during DS at a given withdrawal rate of 0.083 mm/s. Among the microstructural features investigated, the dendrite arm spacings and average size of the MC-type carbide near the chill plate were found to be influenced by the quenching effect of the chill plate. However, no significant influence was found on the size and volume fraction of microporosity, and the volume fraction of the MC-type carbide. The relationship between the microstructural features and the solidification variables was also analyzed and discussed on the basis of a combination of experimental and modeling results.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 제13회 신호처리 합동 학술대회 논문집
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• pp.25-28
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• 2000

In this paper, we choice multicarrier direct-sequence code division multiple access using bandwidth effectively in communication system. Because this system is based on DS-CDMA the same problem is raised. That is, the degradation of the performance is due to multiple access interference. To solve this problem, we proposed the blind adaptive receiver for MC DS-CDMA system. Simulation results show that the proposed blind receiver has more about 0.5(dB) value of SNR than conventional receiver.

• 한국음향학회지
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• 제17권6호
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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.

• 한국전자파학회논문지
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• 제10권3호
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• pp.319-328
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• 1999

한정된 무선자원에서 CDMA 방식의 초고속 이동멀티미디어 통신서비스를 제공하기 위해서는 대역사용효율을 높힐 수 있는 방안이 필요하다. 본 논문에서는 실수 이진 데이터가 입력되는 Binary input Multi Carrier-CDMA전송구조의 IFFT처리부에서 출력 심볼 파형이 대칭성을 갖는 점을 이용하여 중복된 출력 심볼파형의 1/2만을 본래 출력 심볼파형의 시간폭에 맞게 시간 확장을 하므로서 기존 전송대역폭의 1/2대역폭으로 신호전송이 가능한 구조를 제시하였다. 본 방식은 동일 대역폭 사용조건하에서 DS-CDMA방식에 비해 처리이득이 4배 높아지며 그에 따른 성능이 제시되었다.

• 한국통신학회논문지
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• 제25권10A호
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• pp.1486-1491
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• 2000

A Multicarrier system required a lower speed paralled-type of signal processing in contrast to a fast serial processing in a single carrier CDMA system. For the analysis we evaluate MC-CDMA system performance with that of a single-carrier CDMA system and a multi-carrier CDMA system based on the various jamming conditions. Also we studied to the capacity level against the threat environment through the performance comparison in commercial CDMA system and Limiting repeater system. as a result we found that M-CDMA system has a robustness to narrowband interference and multipath environments like as a Rayleigh fading.