Concurrent Vital Sign and Position Sensing of Multiple Individuals Using Self-Injection-Locked Tags and Injection-Locked I/Q Receivers With Arctangent Demodulation

Abstract—This work presents a wireless system that operates in the 2.4 GHz ISM band for concurrently sensing the vital signs and positions of multiple individuals. Characterized by low complexity and high accuracy, the proposed system consists of two main parts. One is a self-injection-locked (SIL) tag carried by a subject, which emits a sinusoidal frequency-modulated (SFM) signal with vital sign information. The other is a group of injection-locked (IL) I/Q receivers, which performs arctangent demodulation of the SFM signal to obtain the position information without using RF refer-ence signals, and simultaneously extracts the vital sign informa-tion of the subject. In the experiment, the system is capable of sensing multiple individuals based on frequency division multiple access (FDMA) technique. Moreover, fidgeting effect on the detec-tion of vital signs has been greatly reduced by a spectral product approach. Accordingly, it is demonstrated that the experimental prototype provides accurate information about the vital signs and positions of different individuals in an indoor environment. Index Terms—Arctangent demodulation, injection-locked (IL) I/Q receiver, self-injection-locked (SIL) tag, vital sign detection, wireless indoor positioning. I