High-Precision and Resilient-to-Interference Ultrawideband Two-Way-Ranging Based on Clock-Less Active Reflector in 65-nm CMOS

An impulse-radio ultrawideband (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 (PPM) 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 narrowband interference (NBI) and multiuser interference (MUI), the sync-word uses a combination of ON–OFF keying (OOK) and 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 semiclosed metal box using omnidirectional antennas.