# Real-Time Indoor Positioning Based on BLE Beacons and Pedestrian Dead Reckoning for Smartphones
###### Abstract  
Nowadays, smartphones have become indispensable in people's daily work and life. Since various sensors and communication chips have been integrated into smartphones, it has become feasible to provide indoor positioning using phones. This paper proposes such a solution based on a smartphone, combining Bluetooth low energy (BLE) and pedestrian dead reckoning (PDR) in the particle filter framework to realize real-time and reliable indoor positioning. First, the smartphone's built-in accelerometer, magnetometer, and gyroscope are used to provide data measurements and formulate a feasible method for PDR. Second, a range-free weighted centroid algorithm is proposed to realize BLE-based localization with low computation complexity. However, a single positioning technology has limitations, e.g., the cumulative error of PDR and the received signal strength fluctuation of BLE. Finally, to exploit the complementary strengths of each technology, a fusion framework utilizing a particle filter is proposed to combine PDR and BLE-based methods and provides more stable and accurate positioning results. Experiments are conducted on a floor in a campus building. Experimental results show that our proposed fused positioning method offers more accurate and stable performance in the long run compared with single PDR or BLE-based positioning. The achieved average positioning error is 1.34 m, which is reduced by 24.16% compared with PDR positioning and 10.60% compared with BLE-based positioning. Moreover, about 95% of the positioning errors are smaller than 1.7 m. The proposed fused positioning method has a vast application prospect in indoor navigation, indoor user tracking, and interactive experience for indoor visitors. p edestrian dead reckoning; Bluetooth low energy; particle filter; smartphone; indoor positioning +
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Nowadays, a smartphone is an integration of communication and measurement devices. On the one hand, it supports Bluetooth low energy (BLE), WiFi, and 4G/5G cellular connectivity for communication. On the other hand, it incorporates various sensors such as an accelerometer, gyroscope, magnetometer, etc., which can be used to provide information on the user's actions [8]. Pedestrian dead reckoning (PDR) [9] is a relative navigation technique that uses these sensor measurements. It consists of four parts: (1) step detection based on an accelerometer, (2) step length estimation based on empirical acceleration models, (3) heading direction estimation between each step based on the gyroscope or magnetometer, and (4) 2D position estimation--noting that in PDR, the user's current position is estimated based on the previous position by calculating the walking distance and the heading direction. It has the merits of good real-time performance and relatively accurate positioning for short-time intervals. Meanwhile, it suffers from large cumulative error when long distances are involved, and it greatly depends on the precision of the previous position [8]. Therefore, PDR is usually utilized in combination with other methods. As for smartphone-based indoor localization, PDR has been combined with BLE [10], WiFi [11], acoustics [2], and magnetic fields [12] in the literature to provide higher positioning accuracy. Among these technologies, WiFi and BLE are the most commonly adopted [8]. By deploying WiFi access points (APs) or BLE Beacon tags in the indoor area, the received signal strength (RSS) obtained by the smartphone can be used to achieve indoor positioning. Compared with WiFi, BLE Beacon tags have the following advantages: they have a small size and low energy consumption, can be placed flexibly in any indoor location without active power supply [8], and cost much less energy to scan for BLE devices than to scan for WiFi APs[13]. Therefore, BLE is more promising than WiFi to become the mainstream technology in the indoor positioning market [14].