The IEEE 802.15.4a standard for impulse radio ultrawide band (IR-UWB) communication systems defines a ranging scheme which relies on the measurement of the round-trip propagation time of electromagnetic pulses. Accuracy is strongly dependent on the estimation of the timeof-arrival (TOA) of the pulse that is spread in time due to multipath propagation. The major concern therefore is the proper detection of the leading edge. In this work, the ranging capabilities of the standard are analyzed for an energy detector receiver. Emphasis is put on the influence of transmitter and receiver parameters, which are evaluated for a set of measured scenarios. It is shown that sub-meter ranging accuracy can be achieved with fixed parameter settings