Frequency Estimation of Vital Sign Signals Using FMCW Radar: A Cramer–Rao Lower Bound Analysis and Experimental Validation

In the next-generation communication technologies, the rise of sensing functionality has created new opportunities, with frequency modulated continuous wave (FMCW) radar promising to be a robust solution for non-contact vital sign detection, thereby enhancing health monitoring systems. In this paper, we present a comprehensive analysis of the frequency estimation problem for vital sign signals using FMCW radar, focusing on the theoretical Cramer–Rao lower bound (CRLB) derivation. Specifically, the exact and closed-form CRLB expressions are derived, incorporating the embedded vital sign information of multipath reflections in the presence of additive Gaussian noise, offering insight into the fundamental limits of estimation accuracy. Simulation results validate the consistency between exact and approximate CRLBs, while experimental results demonstrate the effectiveness of a confidence fusion algorithm in approaching these bounds under realistic conditions.