Reflection Characteristics Analysis of IR-UWB Signal

As one of the most important propagation mechanisms in ultra-wideband (UWB) indoor environment, reflection has its own characteristics due to the huge bandwidth of the UWB pulse. The inherent material dispersions represent the changes of permittivity and conductivity, etc. with frequency, which will cause UWB pulse undergoes waveform distortion in propagation, and furthermore affects the channel modeling and the receiver structure. In this paper, the reflection waveforms of an IR-UWB signal are calculated in two ways: time-domain (TD) and frequency-domain (FD). In TD method we deduce the time domain reflection coefficient from the frequency Fresnel reflection coefficient through some analytical approximations, then convolute with the transmitted pulse to obtain the reflection waveform. In FD method, the frequency dispersion of material is taken into account by uniformly divided the frequency band (2- 11 GHz) into several subbands. Each subband is simulated separately and then combined in the whole bandwidth. Then the final waveform is got by using the inverse discrete fourier transform (IDFT). Two typical indoor materials: wooden door and block are used in the analysis. The results show that the two methods curves agree well, and the reflection waveform of an UWB pulse doesn´t distort apparently. The numerical data also imply that the simple time domain reflection coefficient can be also used to model an UWB pulse´s reflection in the analytical channel modeling.