Analysis of power spectral density for time-hopping impulse ultra-wideband communications system

The power spectral density (PSD) of time-hopping (TH) impulse ultra-wideband (I-UWB) communications system is derived from a general system model. And the main components of PSD are analyzed. The concrete impacts of TH frame structure, different kinds of modulations with time hopping, such as amplitude modulation, phase modulation and their combinations, on PSD are discussed in details. Next, the direct-sequence time-hopping (DS-TH) I-UWB system is introduced and from its PSD analysis, it is found that the use of DS can get rid of the impact of TH on PSD and the PSD is only determined by the energy spectral density of baseband pulse. This can be viewed as a new method to optimize system power-efficiency.