A hierarchical time-domain modulation scheme for wideband communications in a dispersive multipath channel

In this paper a time-domain modulation scheme for ultra-wideband communications is proposed and the performance of such modulation scheme in a highly dispersive channel is evaluated using a coherent and physics-based propagation model. In this scheme a relatively large number of orthogonal waveforms, that are scalable in time and frequency domains (like wavelets), are modulated (pulse position or amplitude modulation) with a piece of information data individually and transmitted through the channel. This scheme offers two major advantages: (1) noting that pathloss and channel characteristics are very much frequency dependent, at least a portion of information reaches distant observation points, (2) each waveform can easily be radiated from a small and relatively narrowband antenna and hence issues related to the design of efficient, dispersionless ultra-wideband antennas is circumvented. This approach also allows for data categorization according to a specific hierarchy. To demonstrate the advantages mentioned and assess the performance of such system, an ultra-wideband wave propagation in a forested environment over a frequency range of 10-210 MHz, is presented.