A comparative study of pulse combining schemes for impulse radio UWB systems

Impulse radio systems transmit a number of ultrawideband pulses for each information bit. In a multiuser scenario, the pulses from a given user may have different signal-to-interference-plus-noise ratio (SIR) and therefore a receiver that combines these signals with equal weight assignment is suboptimal. In this paper, a multiuser impulse radio system over an additive white Gaussian noise channel is considered and the performances of three types of receivers that employ different pulse combining schemes are investigated. Namely, a conventional matched filter receiver, a blinking receiver and a minimum mean square error (MMSE) receiver are considered. Assuming a large number of pulses per information bit, approximate expressions of bit error probability for the conventional matched filter and blinking receiver are presented. Then, conditions under which one receiver has a lower probability of error than the other are obtained. Also an MMSE receiver is proposed, which optimally combines the pulses but has higher complexity compared to the other types of receivers. Simulation studies are employed to compare the performances of the receivers and to verify the analytical expressions.