The need for effective capture of multipath energy presents a key challenge to receiver design for pulsed ultra-wideband (UWB) systems operating in non-line-of-sight propagation environments. Conventional RAKE receivers can capture only a fraction of the received signal energy under practical implementation constraints, and have to deal with stringent synchronization and channel estimation requirements. Transmit-reference and autocorrelation receivers can effectively collect energy from all the received multipath components without explicit channel estimation, but the detection performance is limited by noise enhancement effects and the data rate drops by 50% because of pilot symbol overhead. In this paper, we develop decision-directed autocorrelation (DDA) receivers for effective multipath energy capture at low complexity. Operating in an adaptive decision-directed mode, the proposed DDA methods can considerably lower the noise level in the self-derived template waveform, thus improving overall detection performance. There is little loss in energy efficiency since no reference pilots are required during adaptation. Analytical performance analysis along with corroborating simulations is performed to evaluate the error performance of the proposed receivers in indoor lognormal fading channels