• Title/Summary/Keyword: modified Hadamard code

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Modified Hadamard Codes for Spectral-Amplitude-Coding Optical CDMA (Spectral-Amplitude-Coding Optical CDMA를 위한 Modified Hadamard Code)

  • Jhee, Yoon-Kyoo
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.48 no.8
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    • pp.5-9
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    • 2011
  • Spectral-amplitude-coding optical CDMA systems using codes based upon Hadamard matrices have very restrictive code lengths of $2^n$ and high phase-induced intensity noise(PIIN). In this paper a new code family, namely modified Hadamard code, is proposed to relax the code length restriction and the number of simultaneous users. The improved performance of the proposed system is analysed with the consideration of noise.

A Study on Cross-correlation Control Schemes on Walsh and Golay Codes Based on the Orthogonal Transformation and BER Performance Evaluation of Asynchronous CDMA System Using the Modified Codes (직교변환에 의한 Walsh 및 Golay 코드의 상호상관 제어방식과 수정된 코드를 사용한 비동기 CDMA 시스템의 비트오율 성능에 관한 연구)

  • Lee, Won-Chang;Kim, Myoung-Jin
    • Journal of the Institute of Convergence Signal Processing
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    • v.9 no.4
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    • pp.304-312
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    • 2008
  • Orthogonal codes like Walsh and Golay codes may have large correlation value when they are not synchronized, hence they are seldom used in asynchronous CDMA systems. Wysocki[1] showed that by multiplying the original Walsh-Hadamard matrix with an orthogonal transformation matrix the resultant matrix sustains orthogonality between row vectors and their cross-correlation can be reduced. Soberly and Wysocki[2] proposed similar scheme on Golay codes. This implies that using the proper orthogonal transformation cross-correlation of Walsh and Golay codes can be reduced, and the transformed codes can be used for user separation in the CDAM reverse link. In this paper we discuss cross-correlation related parameters which affect the performance of an asynchronous CDMA link, and we investigate the correlation properties of the transformed codes. When we designed orthogonal transformation matrices for Walsh and Golay codes, we minimized the maximum value of aperiodic cross-correlation of the codes ($ACC_{max}$) or the mean square value of the aperiodic cross-correlation($R_{cc}$) with preserving the orthogonality of the modified codes. We also evaluate the asynchronous CDMA system that uses the transformed Walsh and Golay codes.

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