RIS-Based Communication and Anti Passive Sensing System (RIS-CAPS): Privacy Performance and RIS Configuration Study

Passive sensing has garnered substantial attention in e-healthcare and smart home applications for the appealing concept of detecting human occupancy and activities based on channel state information (CSI) in wireless signal transmissions. Despite the promising benefits of passive sensing, what is less mentioned is the privacy issue raised. It is difficult to prevent a communication device from analyzing CSI to learn private environmental information. This paper investigates the use of a reconfigurable intelligent surface (RIS) by a system planner (SP) to assist a user device (UD) Communication and meanwhile Anti its Passive Sensing based on CSI, named RIS-CAPS. We address the fundamental UD passive sensing performance in identifying changes in the environment, called environmental states, by CSI estimation and reveal the tradeoff between communication and system privacy when a RIS is controlled to influence wireless channels. We report a shortboard effect that to anti UD’s sensing, the UD’s communication performance in different environmental states will be determined by the state having the worst channel condition. Furthermore, we analyze and tackle the new RIS configuration optimization problem to improve UD’s communication while constraining its passive sensing performance. A solution algorithm that exploits alternating optimization and semidefinite relaxation techniques is developed to address the challenging RIS configuration optimization. Finally, extensive simulations validate the performance modeling and analysis in our study. Insights into when RIS is more capable to anti passive sensing are provided.