Ultra-wideband technology promises unique advantages over conventional narrowband communications systems. However, the potential interference of ultra-wideband devices to existing narrowband systems is an issue of serious concerns. In this paper, the mathematical models for describing two impulse modulation schemes, namely the biphase modulation and the hybrid modulation, are reviewed. A period extension method and two implementations for PN sequence in the impulse train used to generate ultra-wideband signal are proposed. Considerable reduction in the power spectral density level can be obtained by use of this period extension technique. An example using m-sequence is given, which demonstrates a near-white ultra-wideband spectrum.
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