This paper considers ultra-wideband (UWB) based localization of mobile users in indoor environment. Because of severe multipath indoor localization still presents a challenging issue and UWB is often considered as technology enabling precise localization. Typically for UWB Time of Flight (TOF) based approaches like Time of Arrival (TOA) or Time Difference of Arrival (TDOA) are applied. Recently also localization based on Received Signal Strength (RSS) is gaining more interest, where position of the transmitting device is calculated based on the RSS on several Base Stations (BS) with known positions. To perform the positioning the transmit power must be known. This paper considers Received Signal Strength Difference (RSSD) based positioning, which does not require the knowledge of the transmit power. The positioning is further assisted with TDOA measurement. It is shown that including only one single TDOA information improves the localization performance significantly.