Method and system for contactless vital sign monitoring

The invention relates to a method for vital sign monitoring using a radar sensor system (1), the radar sensor system (1) comprising a transmitter (2), a receiver (3) and processing device (5), wherein: the transmitter (2) irradiates (100) at least one body region (21) of a person (20) with radar radiation (30); the receiver (3) generates (110) a receiver signal from reflected radiation (11) from the at least one body region; the processing device (5) generates, for each of a plurality of processing windows, a displacement signal based on the receiver signal, which displacement signal characterizes a body motion comprising as oscillating motions a breathing motion and a heartbeat motion, and calculating an estimated fundamental frequency for at least one oscillating motion. In order provide reliable and efficient means for life sign monitoring, the invention provides that the processing device (5), based on the displacement signal, applies an adaptive Nonlinear Least Squares method to calculate (250) a plurality of frequency estimates (fr1, fr2, fr3), each of which corresponds to one of a plurality of harmonics of a first oscillating motion, wherein the processing device (5) uses an individual search region (Ah1, Ah2, Ah3) for each frequency estimate (fr1, fr2, fr3), adapts at least one search region (Ah1, Ah2, Ah3) for at least one processing window, and calculates (300) a first estimated fundamental frequency (fh) for the first oscillating motion based on the frequency estimates (fr1, fr2, fr3).