One of the challenges in direct conversion Doppler radar lies in the dc offset resulted from antenna coupling. The dc offset may saturate the baseband amplifiers, preventing sufficient amplification of the received signal. In this work, a Coupling-Cancellation-Antenna (CCA) was implemented in the radar front end to enhance radar detection accuracy by minimizing the TX-RX antenna coupling. The idea is to have two transmitting antennas fed by signals with 180° phase difference such that the two signals cancel at the RX antenna. As a result, a larger receiver gain can be used to improve the signal to noise ratio without saturating the baseband output. Experimental validations of the CCA concept demonstrate 37-dB reduction in the TX-RX coupling. Furthermore, the CCA method reduces the detection error from 15.8% to 2.4%.
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This content will become publicly available on May 31, 2025
Room-scale Location Trace Tracking via Continuous Acoustic Waves
The increasing prevalence of smart devices spurs the development of emerging indoor localization technologies for supporting diverse personalized applications at home. Given marked drawbacks of popular chirp signal-based approaches, we aim at developing a novel device-free localization system via the continuous wave of the inaudible frequency. To achieve this goal, solutions are developed for fine-grained analyses, able to precisely locate moving human traces in the room-scale environment. In particular, a smart speaker is controlled to emit continuous waves at inaudible20kHz , with a co-located microphone array to record their Doppler reflections for localization. We first develop solutions to remove potential noises and then propose a novel idea by slicing signals into a set of narrowband signals, each of which is likely to include at most one body segment’s reflection. Different from previous studies, which take original signals themselves as the baseband, our solutions employ the Doppler frequency of a narrowband signal to estimate the velocity first and apply it to get the accurate baseband frequency, which permits a precise phase measurement after I-Q (i.e., in-phase and quadrature) decomposition. A signal model is then developed, able to formulate the phase with body segment’s velocity, range, and angle. We next develop novel solutions to estimate the motion state in each narrowband signal, cluster the motion states for different body segments corresponding to the same person, and locate the moving traces while mitigating multi-path effects. Our system is implemented with commodity devices in room environments for performance evaluation. The experimental results exhibit that our system can conduct effective localization for up to three persons in a room, with the average errors of 7.49cm for a single person, with 24.06cm for two persons, with 51.15cm for three persons.
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- Award ID(s):
- 2019511
- NSF-PAR ID:
- 10529768
- Publisher / Repository:
- ACM
- Date Published:
- Journal Name:
- ACM Transactions on Sensor Networks
- Volume:
- 20
- Issue:
- 3
- ISSN:
- 1550-4859
- Page Range / eLocation ID:
- 1 to 23
- Subject(s) / Keyword(s):
- Ultrasonic sensing, smart home, localization
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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