This study investigates the spectrum shaping observed in ultra-wideband (UWB) communications. An auxiliary independent signal (AIS) to limit undesired spectral lines because of periodicity or unbalanced data sources (i.e. nonuniformly distributed) and or non-symmetric data modulation schemes are introduced. Each transmitted symbol is represented by a preamble AIS pulse followed by a set of transmitted data pulses that are weighted, delayed and summed in accordance with a predefined modulation. The use of the fifth derivative Gaussian pulse ensures that the UWB spectrum mask established by the Federal Communications Commission (FCC) is met, and a preamble signal is designed to eliminate spectral lines at specific frequencies that appear mainly by existing balanced or unbalanced binary data sources. A unified spectral analysis is adapted for general uncorrelated and correlated quaternary bi-orthogonal modulations. An optimisation problem is also introduced in the case of unbalanced data sources in order to minimise undesired spectral lines subject to comply with the FCC spectrum mask and maximise spectral utilisation.
