An impulse-radio ultra-wideband (IR-UWB) two-way ranging (TWR) system for indoor and harsh environments is described. In the proposed system, a synchronization (sync) word with a specific sequence of UWB impulses and with a particular pulse-position modulation is transmitted from the anchor, and then detected by the tag using a continuous-time sync detection mechanism. Then the tag instantaneously reflects a similar sync- word back to the anchor. Finally, the anchor detects the sync-word using the same continuous-time sync detection mechanism as the tag. The Time of Flight (ToF) between the transmitted sync and the received sync on the anchor is then calculated to measure the distance between the transmitter and the receiver. Unlike common TWR systems, here in the tag, a clock-less active reflector is used which reduces sync detection and reply time, and hence, increases the ranging accuracy due to the mitigation of clock drift. To reduce narrow band interference (NBI) and multiuser interference (MUI), the sync-word uses combination of on-off-keying (OOK) and pulse-position modulation (PPM). The proposed sync-word detector continuously verifies the presence of UWB impulses having the correct time intervals. As a proof-of-concept, a 4-bit sync-word is utilized, although the technique can be directly expanded to longer sync-words. The proposed system is fabricated using a 65 nm CMOS integrated circuit technology. Experimental results show the accuracy and resilience- to-interference (NBI and MUI) of the proposed TWR. The technique shows a 1.2 cm standard deviation for the accuracy of a single-measurement TWR in a semi-closed metal box using omnidirectional antennas.

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