This paper presents positioning results determined by a multi-layer, packet based OMNet++ simulator for communication and positioning in an autonomous wireless sensor network. The simulator includes an IR-UWB physical layer model considering the impact of multi-user interference, a highly flexible MAC layer which performs physical layer adaptations to optimize the total link performance, and a ranging and positioning module. We will give an estimation of the positioning accuracy of the system by considering ideal, LOS and NLOS channel conditions.