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In the past decades, continuous Doppler radar sensor-based biosignal detections have attracted many research interests. A typical example is the Doppler heartbeat detection. While significant progresses have been achieved, reliable, time-domain accurate demodulation of biosignals in the presence of unavoidable direct current (dc) offsets remains a technical challenge. Aiming to overcome this difficulty, we propose in this article a novel demodulation algorithm that does not need to trace and eliminate dynamic dc offsets based on approximating segmented arcs in a quadrature constellation of sampling data to directional chords. Assisted by the principal component analysis, such chords and their directions can be deterministically determined. Simulations and experimental validations showed full recovery of micrometer-level pendulum movements and strongly noised human heartbeats, verifying the effectiveness and accuracy of the proposed approach. [ABSTRACT FROM AUTHOR]

Many radio frequency measurement systems require multicarrier signals with coherent phases between carriers with different frequencies. A typical example is the signal generator which is used in multicarrier multipactor (MM) testing systems. In this paper, we propose a new approach for the generation of coherent multicarrier signals based on a state-of-the-art phase-locked loops technique. Different from existing systems that rely on a heavy use of commercial microwave instruments, this generator can be implemented with on-shelf chips and devices. As an example, an ultrahigh frequency band generator is implemented and how to implement the in-system calibration of this generator in an experimental multipactor testing system is demonstrated. Based on the proposed approach, performing a quantitative experimental research on MM becomes affordable for an ordinary microwave laboratory, which may promote the in-depth experimental study in this area. It can also be used in a wide range of applications such as MIMO and phased array systems. [ABSTRACT FROM AUTHOR]

Recently, progresses have been made in hand gesture recognition based on Doppler radar sensors. However, it remains a technical challenge to avoid the interfering human motions. An example is detecting hand gestures in the presence of random body movements. In this paper, we propose a solution based on a Single-input Multiple-output frontend and a blind motion separation algorithm. Assisted by an additional receiving channel, Doppler signals caused by different motions can be separated by extending the algorithm originally developed for separating human voices. The experimental separation of hand gestures from interfering movements verified the effectiveness of this approach. The proposed solution can be potentially used in novel applications such as human gait and gesture recognitions. [ABSTRACT FROM AUTHOR]

With the growing demands for localizing humans and mobile service robots, wireless indoor positioning has become a hot topic. Due to inevitable multipath scatterings in indoor spaces, technical challenges still exist. In this paper, we propose a new solution based on vertically uniform alternating magnetic fields. Such fields can be established by long coils driven by watt-level alternating currents with hertz-scale frequencies. Detected by commercial magnetic sensors, the coexisting dual-frequency magnetic fields are able to distribute in indoor spaces with tens of square meters. With 104-km-scale wavelengths, indoor obstacles can be considered as negligible Rayleigh scatters, and thus, this method is robust in complex indoor environments. Insensitive to height, the vertically polarized magnetic fields can be conveniently detected by existing smartphones, implying a human-oriented WIP based on smartphones. [ABSTRACT FROM AUTHOR]

Utilizing microwave continuous-wave Doppler radars to wirelessly detect mechanical vibrations have been attracting more and more interests in recent years. In this paper, aiming to solve the null point and nonlinear issues in small-angle approximation-based Doppler radar sensors and eliminate the codomain restriction in the arctangent demodulation approach, we propose and investigate an extended differentiate and cross-multiply (DACM) algorithm. With an additional accumulator, the noise performance of the original DACM algorithm is improved. Moreover, the amplitude information of the vibration can be directly retrieved from accumulation without involving any distance-dependent issue. Experimental validations show that the proposed algorithm can fully recover the vibration patterns with the measured noncalibrated amplitude agreeing well with the known precalibrated data. Application examples of mechanical fault detection and human vital sign detection are demonstrated, showing a wide range of potential applications of this algorithm. [ABSTRACT FROM PUBLISHER]