Nonlinear Effect of Direct-Sequence CDMA in Optical Transmission


IEICE TRANSACTIONS on Communications   Vol.E78-B   No.5   pp.702-708
Publication Date: 1995/05/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Issue on Optical Signal Processing and Its Applications to Telecommunications)
laser diode nonlinearity,  direct-sequence CDMA,  optical transmission,  

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The intermodulation distortion (IMD) due to laser diode (LD) nonlinearity of an asynchronous direct-sequence code division multiple access (DS/CDMA) system in optical transmission is analyzed. A third-order polynomial without memory is used to present LD nonlinearity. In DS/CDMA systems, only one harmonic of the third-order inter-modulation term falls on the signal frequency band and influences the system performance. The average distortion is derived with only the information of autocorrelation functions. The results are useful for CDMA system design and performance analysis. With LD nonlinearity it is necessary to select an optimal modulation index that provides a maximum signal-to-noise ratio (SNR). The analytical method is applicable to other general nonlinearities in CDMA systems.