High-Resolution OFDM-Based Sensor Node Ranging Within In-Homogeneous Media of Human Body

This paper introduces an effective ranging technique for sensor nodes implanted within human body leveraging a novel merger of high-resolution time-of-arrival (ToA) and direction-of-arrival (DoA) estimations. Human body is an in-homogeneous media (IHM) consisting of frequency dispersive sub-media (body organs) with unknown thicknesses that entail addressing two open problems: 1) high-resolution ToA estimation of a wideband ranging waveform propagated within IHM consisting of multipath and dispersive channels and 2) calculation of straight line range between implanted sensor node and receiver sensor array on human body. In the proposed technique, pre-allocated orthogonal frequency division multiplexing is utilized to construct a ranging waveform leveraging equally spaced and orthogonality properties of its sub-carriers which enable high-performance ToA estimation in frequency domain. The estimated ToA, however, cannot be utilized to calculate the straight line range due to refraction of propagated waveform at sub-media boundaries. Therefore, a merger of ToA and DoA is proposed that exploits multiple measurements at different carrier frequencies to develop a system of linear equations. The straight line range, then, is estimated by solving this system of equations with respect to thicknesses of available sub-media. The exploited approximations are discussed and verified via theoretical evaluations and simulations for human body to prove the feasibility of the proposed technique.