Abstract:

In an ultra wideband (UWB) impulse radio (IR) system, a number of pulses, each transmitted in an interval called a \"frame\", is employed to represent one information symbol. Conventionally, a single type of UWB pulse is used in all frames of all users. In this paper, IR systems with multiple types of UWB pulses are considered, where different types of pulses can be used in different frames by different users. Both stored-reference (SR) and transmitted-reference (TR) systems are considered. First, the spectral properties of a multi-pulse IR system with polarity randomization is investigated. It is shown that the average power spectral density is the average of the spectral contents of different pulse shapes. Then, approximate closed-form expressions for the bit error probability of a multi-pulse SR-IR system are derived for RAKE receivers in asynchronous multiuser environments. The effects of both inter-frame interference (IFI) and multiple-access interference (MAI) are analyzed. The theoretical and simulation results indicate that SR-IR systems that are more robust against IFI and MAI than a \"conventional\" SR-IR system can be designed with multiple types of ultra-wideband pulses. Finally, a multi-pulse TR-IR system is proposed, in which the transmitter and the receiver are designed in order to mitigate the effects of IFI and MAI. The performance of the proposed receiver is analyzed approximately and by simulations.