I. Introduction
Along with the booming requirement of the location-based service, device-free localization (DFL) has received much attention recently due to the advantage that the target does not need to carry any devices. In the past, most researches about device-free localization systems are based on cameras [1] or radio frequency (RF) devices [2]. However, some inherent defects of cameras and RF devices continuously limit their application in environments of low-light, privacy concern, and cost restriction [3]. To conquer the above limitation, more and more researchers propose to utilize pyroelectric infrared (PIR) sensors to achieve device-free localization [3]–[15]. Compared with the camera-based systems, the PIR-based systems work well in low-light environments and have fewer privacy concerns, because they detect persons through sensing their infrared radiation. Compared with the RF-based systems, PIR-based systems have much lower cost and energy consumption. Typically, the price of a PIR sensor is less than 1 dollar, and the power consumption of a PIR sensor is only about 50uW [16].