# UWB-Based Real-Time Indoor Positioning Systems: A Comprehensive Review
## 5 Real-Time UWB Indoor Positioning Systems (RTIPSs)
### Indoor Positioning Systems for Robotics Applications  
The indoor positioning systems of mobile robots are essential and indispensable, especially in swarm robotics, simultaneous localization and mapping (SLAM), and large-scale applications. From the perspective of functionality and practicality, the UWB-based IPS is more suitable than other technologies for robotics applications [121]. In this section of the paper, we will review the most important integrated works and research in this field. We consider the systems that contain all of the main parts of RTTSs, such as the hardware components that allow the indoor tracking and positioning operation with the UWB technology, along with the interactive software to show and monitor the relative location information and object coordinates in a graphical user interface. The integrated system can simulate the physical reality in real time in the software, enabling real-time tracking with the best possible accuracy. Figure 12 gives an example representing the real-time tracking system in a Python-based monitoring program. There are many works related to this topic. [PERSON] et al. [122] proposed an extensible RTLS for mobile robots. The system consisted of one tag fixed on the mobile robot, five anchors (four fixed and one with an unknown position), a camera, and an IMU. The UWB anchors did not require clock synchronization. This system can be extended by adding a new anchor, where the recursive least squares (RLS) approach is used for the new anchor's location estimation, and the maximum correntropy Kalman filter (MCKF) is used to fuse the data from the UWB network and IMU. The system's main hardware included the DecaWave DWM1000 transceivers for the UWB tag and anchors with a small mobile robot equipped with the KY-INS110 IMU unit (Beijing BDStar Navigation Co., Beijing, China), and MYNT EYE D1000-IR-120 stereo camera (MYNT AI, Jiangsu, China). The system tests indicated a 0.137 m root-mean-square error (RMSE) in the positioning location. [PERSON] et al. [4] proposed a UWB-based RTLS for mobile mining robots in harsh coal mine environments. The system used both UWB technology for location and IMU sensors for orientation to enhance its positioning accuracy. Four anchors and one tag were used to perform a 3D  
Figure 12: IPS: (**a**) real-time testing environment; (**b**) 2D simulated environment with real-time object tracking using Python [80]. positioning in the coal mine using the P440 UWB module (TDSR LLC., Petersburg, TN, USA). The MTi-G-710 motion tracker IMU module (Movella Inc., Henderson, NV, USA) was used to provide the robot's orientation data. The UWB tag and the IMU modules were fixed on the mobile tank robot. The data of both the UWB and IMU modules were fused using the error-state Kalman filter (ESKF). The system tests indicated that a localization accuracy of \(\approx\)20 cm can be achieved. [PERSON] et al. [123] proposed a Kalman filter-based IPS for mobile robots. Their work aimed to mitigate the multipath issue of the UWB waves using the M-estimation robust Kalman filter (M-RKF) and leveraging an adaptive empirical variance model. The system hardware used the Qorvo DW1000 modules for both the anchors and tag, where the tag was fixed in a mobile ground robot surrounded by four fixed anchors. The TWR protocol was used for range measurements. The movable tag acquired all of the range measurements at a 280 Hz refresh rate. The practical system tests indicated that the use of M-RKF enhances the system localization performance by 14% in LoS and 31% in NLoS environments. [PERSON] et al. [124] developed an IPS for mobile robots by integrating the filtering methods moving average (MVG), Kalman filter (KF), and extended Kalman filter (EKF) with a low-pass filter (LPF). The used hardware included the commercial POZYX UWB positioning system (POZYX, Ledeberg, Belgium) and the open-source ROS-based TurtleBot3 mobile robot (ROBOTIS Inc., Tokyo, Japan).