Digital receivers for future high-rate high-bandwidth communication systems will require large sampling rate. This is especially true for ultra-wideband (UWB) communications with impulse radio (IR) modulation. Due to high complexity and large power consumption, multibit high-rate analog-to-digital converter (ADC) is difficult to implement. Monobit receiver has been previously proposed to relax the need for high-rate ADC. In this paper, we derive optimal digital processing architecture for receivers based on monobit ADC with a certain over-sampling rate and the corresponding theoretically achievable performance. A practically appealing suboptimal iterative receiver is also proposed. Iterative decision-directed weight estimation, and small sample removal are distinctive features of the proposed detector. Numerical simulations show that compared with full resolution matched filter based receiver, the proposed low complexity monobit receiver incurs only 2 dB signal to noise ratio (SNR) loss in additive white Gaussian noise (AWGN) and 3.5dB SNR loss in standard UWB fading channels.