| The Global Positioning System (GPS) nowadays is sized down to a chip sensor and built into almost every smart phone and tablet. Therefore, navigation using those intelligent gadgets becomes a must-have function. GPS has been widely employed for outdoor navigation, while its performance suffers from severe degradation in challenging scenarios such as urban canyon and indoor. Due to the overwhelming signal noise, building reflection and blockage, indoor navigation using GPS frequently encounters poor accuracy or even signal outage. In order to improve the service availability and navigation accuracy, inertial measurement units (IMU) are integrated with GPS, which continuously measures the user acceleration and rotation rate. Integrating these relative motion measurements derives the position, velocity and orientation, therefore it bridges the gap during GPS outage. However, IMU raw measurements are contaminated by sensor bias and drift, and for low-cost sensors on smart devices, the bias and drift are extremely severe and unstable. The navigation solution derived from these poor quality sensors results in significant accumulative errors, which will destroy the system reliability very soon. Furthermore, most smart devices embrace cellular and Wi-Fi network positioning to improve service availability, time-to-first-fix, accuracy and reliability in indoor scenarios. Unfortunately, network based positioning performance highly depends on the signal reception, and quality of the database of Wi-Fi access points (APs) and cellular towers. Based on our experiments, network based positioning performance can merely achieve tens of meters position accuracy on average. For indoor navigation application, however, users' expectation is roomlevel, turn-by-turn navigation guidance. |
