Spectrally shaped generalized multitone direct sequence spread spectrum

In this paper, a new modulation scheme that is called spectrally shaped generalized multitone direct sequence spread spectrum (SSG-MT-DS-SS) is proposed. This scheme enables moderate shaping of the transmitted spectrum without the use of spectral-shaping filters; instead, the spectrum is shaped by appropriate selection of the parameters of each subcarrier. These parameters are amplitude, data rate, processing gain, and the frequency separation between adjacent subcarriers. Since these parameters are selectable, this scheme is a completely generalized MT-DS-SS approach. Analysis and simulation results show that by properly choosing these parameters, the level of the spectral sidelobes can be reduced, while slightly changing the width of the mainlobe and simultaneously obtaining a good error-probability performance, on both additive white Gaussian noise and dispersive fading channels. For even a small number of subcarriers (e.g., 3-5), spectral sidelobes can be reduced by 3-6 dB from those of the conventional MT-DS-SS spectrum, with little or no degradation in error-probability performance. For larger numbers of subcarriers, additional sidelobe reductions are attainable. In addition, the SSG-MT-DS-SS system has a smaller peak-to-average power ratio than the conventional MT-DS-SS when the amplitudes of each subcarrier are not identical.