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Design principle of colored-noise tolerant optimum despreading-code sequences for spread-spectrum systems

To improve demodulated signal to noise ratios for colored noise environments, a new direct-sequence spread-spectrum receiver system which has the function of shaping demodulated chip waveforms has been proposed. This function modifies the frequency characteristics of the damp-integrated output to be applied to the decision circuit. This principle is applied here to construct a whitening filter with which an optimum receiver can be implemented. A theory which provides the maximum SNR by designing the best despreading code sequence for a given spreading code sequence is derived for conditions where an additive colored noise spectrum is given. The performance is analyzed and the results of computer simulation are shown. It is consequently verified that a large SNR improvement can be achieved over conventional systems.