Harmonic Suppression Phase Gradient Demodulation for Vital Sign Monitoring

Radar-based vital sign monitoring, a promising technique for medical guidance and versatile applications, faces challenges in complex environments with low signal-to-noise ratio and substantial interference. This article focuses on accurate vital sign frequency estimation, particularly for weak heartbeat estimation in the presence of substantial harmonics interference. This innovative method involves constructing an enhanced multiplication spectrum and performing harmonic order recognition to effectively eliminate the effect of cardiopulmonary intermodulation, thereby ensuring accurate respiration frequency estimation. Moreover, we utilize the spectral redundancy in the second-order cyclic temporal moment function (CTMF) to derive the heartbeat frequency via a harmonic and cross-term (CT) suppressed enhanced spectrum. By establishing a harmonious coupling between respiration harmonics and heartbeat estimation, the proposed approach significantly improves the local signal-to-interference-plus-noise ratio (SINR) of weak heartbeat signals and thus acquires an enhanced heartbeat estimation, even in the substantial respiration harmonics interference. Simulations and experiments validate its superiority over conventional demodulation techniques.