• Title/Summary/Keyword: 준동기 부호

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Access timing offsets-resilient uplink OFDMA for satellite systems (액세스 타이밍 오차에 강한 위성 시스템 상향링크 OFDMA 기법)

  • Kim, Bong-Seok;Choi, Kwon-Hue
    • Journal of Satellite, Information and Communications
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    • v.5 no.2
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    • pp.92-96
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    • 2010
  • We propose a new satellite OFDMA(Orthogonal Frequency Division Multiple Access) scheme with greatly enhanced tolerance of timing offset among the users. In uplink OFDMA systems, timing misalignment among users destroys subcarrier orthogonality and thus, it degrades the performance. In order to avoid this performance degradation, the accurate processing, so called 'ranging', is required to synchronize among users. However, ranging scheme is not available in the satellite systems due to the very long round trip delay. Exploiting the property that PSW(Propoerly Scrambled Walsh-code) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed OFDMA achieves MAI free performance with the timing offset up to ${\pm}1$ OFDM symbol duration for the satellite systems.

Access timing offsets-resilient SC-FDMA (접속동기 오차에 강한 SC-FDMA 기법)

  • Kim, Bong-Seok;Choi, Kwonhue
    • Journal of Satellite, Information and Communications
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    • v.7 no.3
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    • pp.26-29
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    • 2012
  • In this paper, we propose a Single Carrier Frequency Division Multiple Access(SC-FDMA) scheme with greatly enhanced tolerance of timing offset among the users. The type of the proposed scheme is similar to code spread Multiple Carrier Direct Spread Code Division Multiple Access(MC DS CDMA). The proposed scheme performs partial Discrete Fourier Transform(DFT) in order to solve high Peak to Average Power Ratio(PAPR) of the MC DS CDMA before Inverse Fast Fourier Transform(IFFT). Exploiting the property Properly Scrambled Walsh-Hadamard(PSW) code has zero correlation despite ${\pm}1$ chip timing offset, the proposed scheme achieves Multiple Access Interference free performance with the timing offset up to ${\pm}1$ OFDM symbol duration with low PAPR. In contrast, the other existing schemes in comparison undergo severe performance degradation even with small timing offset in multipath fading channel.

Construction Method of Binary Low Correlation Zone Sequence Set Using Gray Mapping (Gray 사상을 이용한 이진 낮은 상관구역 수열군의 생성법)

  • Jang, Ji-Woong;Kim, Young-Sik;Lim, Dae-Woon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.2C
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    • pp.169-174
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    • 2009
  • In this paper, we propose a new construction method of binary low correlation zone (LCZ) sequence set. New construction method applies Gray mapping to conventional quaternary LCZ sequence set that has specific property. The period of new binary sequence set is twice as that of used sequence set in construction, and maximum magnitude of correlation value within the LCZ and cardinality of new set is also twice as those of used quaternary sequence set. But the LCZ size is the same with that of used sequence set. If the used Quaternary sequence set is optimal, the constructed binary sequence set is optimal with high probability.

Inter-user Quasi-synchronous OFDMA for Cooperative Base Stations Systems (상향링크 협력기지국 시스템을 위한 사용자 간 준동기 OFDMA 기법)

  • Kim, Bong-Seok;Choi, Kwonhue
    • Journal of Satellite, Information and Communications
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    • v.9 no.1
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    • pp.97-101
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    • 2014
  • We propose a timing-offset resilient OFDMA with achieving full diversity for uplink cooparative base station (BS) systems. In uplink OFDMA, timing offset (TO) among multiple users destroys subcarrier orthogonality and thus, it degrades the performance. In order to avoid this performance degradation, the accurate processing, so called 'ranging', is required to synchronize. However, in cooparative BS systems, it is difficult to perform ranging scheme. This is because if the ranging scheme is performed for a specific BS, timing offset has to occur for other BSs. Thus, the conventional ranging method cannot achieve full diversity gain in cooperative BS systems. By employing TO resilient OFDMA, so called, 'ZCZ time-spread OFDMA'. we achieve full diversity gain even with TO among multiple users. We show that the proposed scheme achieves the same performance with case of no multiple acces interference.