# A Hybrid Marker-Based Indoor Positioning System for Pedestrian Tracking in Subway Stations
## 1 Introduction
However, GPS is not typically used for indoor positioning because the signal attenuates considerably in indoor spaces. In addition, there are many absolute positioning approaches, which represent fixed coordinates, using various sources such as RFID [10], LED [11], and ultrasound technologies [12]. Sensor-based positioning, which is widely used for estimating a relative position change, can be independently used to compare positioning technology based on wireless communication infrastructure. Independent positioning is possible even in an infrastructure-free environment. Moreover, relative positioning has complementary characteristics with existing wireless-communication-infrastructure--based positioning technology as this method provides high positional accuracy within a short space of time. Accelerometer, gyroscope, compass, magnetometer, barometer, etc., sensors can be used in this field. In particular, an approach called the pedestrian dead reckoning (PDR) method can be used, whereby the accelerometer, gyroscope, compass, or magnetometer are grouped together and used to estimate relative position changes. The PDR method, which uses the sensor data of the gyroscope, accelerometer, and magnetometer embedded in smart devices, is used for tracking the user's location [13; 14; 15]. Depending on the research, the sensors for heading detection may be gyroscope, compass, or magnetometer sensors,. The PDR method uses the acquired data of these sensors to measure step count, stride, and heading estimation. Although research on pedestrian tracking using the PDR method is underway, it is difficult to develop a complete approach because of the numerous variables such as user height, walking pattern, and behavior habits. Because the PDR method cannot be used alone to find the initial location, it is a typical way of combining other sensors, which are then used for the absolute position estimation. As we have seen thus far, the technologies and methods used for indoor positioning are diverse and actively studied. However, it is difficult to apply these technologies to special environments such as subway stations due to the uncertainty of environmental factors, which may negatively affect sensor readings. To address these difficulties, we propose a hybrid-marker-based indoor positioning system (HMIPS) that uses quick response (QR) and augmented reality (AR) techniques that provide AR-based indoor navigation services for pedestrians through viewing on smartphone camera screens. By usinga marker such as a QR code, the positioning can be free from environmental factors caused by the specificity of subway stations, and various application services can be provided. In this regard, we will take a closer look at vision- and QR-based indoor positioning in the next section. In the proposed HMIPS, when a subway station is identified requiring the provision of such a service, it is possible to perform activities such as marker installation, printing, and positioning algorithm modeling using a planning tool provided by the system. In addition, an indoor navigation application without an indoor map provides a UI that displays location information on the screen and provides visual recognition when the user reaches a specific destination. In this app, differentiated navigation is possible according to disabled or general users. An experiment was conducted on an actual subway station to verify the improvement in tracking accuracy and its practical use in the real world. The proposed system achieved a 20% improvement in the subway station compared to the un-corrected inertial sensor data. With more accurate user tracking, these results can be applied to provide practical indoor navigation services for subway station users. The remainder of this paper is organized as follows: Section 2 introduces related research on various image-based and marker-based indoor positioning methods. Section 3 presents the proposed HMIPS and its functions. Section 4 presents and analyzes the evaluation results obtained for the proposed system.