“…In particular, compared with the traditional homogeneous optical imaging and infrared sensing, the RF signal-based sampling and measurement not only have the advantages of wide coverage, feasibility of penetrating obstacles, low cost, low power consumption, and flexible configuration, but also the superiorities of motion-specific sensing and privacy invasiveness. As a result, device-free radio sensing has recently become one of the most promising tomography imaging methods and has formed many practical applications, ranging from target localization and tracking in indoor and outdoor environment [ 23 , 24 ], through to respiratory monitoring [ 25 ], motion recognition [ 26 , 27 ], and elderly fall detection [ 28 , 29 ]. However, to the best of our knowledge, little literature has been focused on the biometric sensing of walking modality by using RF links.…”