Human Proximity Detection and Power Control Based on Antenna Sensing for EMF Touch Compliance of Indoor Base Stations

Small-cell indoor base stations (BSs) are intended to extend network coverage inside buildings and support reliable, high-performing cellular services and Internet of Things (IoT) applications. To gain full installation flexibility, it is desirable to minimize the electromagnetic field (EMF) compliance distance of indoor BSs. To this end, this study proposes a novel approach that enables indoor BSs to adjust their transmitted power dynamically based on human proximity, without requiring the use of specialized sensors. The proposed solution involves a dedicated patch antenna, designed for both robust proximity detection and wireless communication. Proximity detection is achieved by monitoring the variation in the reflection coefficient of the antenna that occurs when a human body is nearby. With this approach, the measured reflection coefficients for various distances between the antenna and a human phantom match well with simulations, showing a detectable distance up to 260 mm. The measured 10-g specific absorption rate (SAR) of the proposed antenna system remains below the regulatory limit at any distance from the BS, resulting in EMF touch compliance. The proposed human proximity detection and power control system can be used as a practical solution to simplify indoor BS installations without unnecessarily reducing the transmitted power under normal operating conditions.