Spread-spectrum signals: attaining rectangular power spectral density with constant carrier envelope

A means is proposed for attaining the twin goals of a rectangular power spectral density (PSD) and a constant-carrier envelope for direct-sequence code division multiple-access (DS-CDMA) waveforms. Mitigation bandwidth is shown to be an especially appropriate metric for CDMA waveforms. Shaping of the PSD structure is explored using the M-ary orthogonal CPFSK modulation format. An important consequence for this type of signal is that the Shannon channel capacity is maximized when the PSD is made rectangular. The results of this exploration highlight the steady decrease in out-of-band power as the number of bits per symbol is increased.