This document proposes a real-time indoor navigation system that fuses Wi-Fi RSSI readings, IMU sensor data, and floor plan information using an enhanced particle filter. The system achieves high accuracy indoor localization on smartphones. Experimental results show the system can automatically recover from localization failures and achieve an average tracking error of 1.15 meters with 90% accuracy within 1.8 meters. The key aspects of the system include fusing Wi-Fi RSSI, IMU sensors, and a discretized graph-based floor plan representation into a particle filter for location estimation, and using efficient filtering to mitigate errors from low-quality IMUs and magnetic disturbances.