**6.1 Sensor fusion**

The use of higher quality inertial/magnetic sensor modules will improve positioning accuracy but the cost of such a solution is often much higher. An alternative solution is to use various positioning data from multiple sources such as radio navigation aids and additional sensors onboard. Through the control applied to the drift error, a positioning system using multiple data sources "fused" together is able to outperform a system using a single data source. Complementary filtering techniques were used to integrate data from different positioning aids in the past. Nowadays, Kalman filtering is popular in combination of two estimates of a variable. For example, IPS data can be integrated with GPS data to provide enforced positioning ability in both indoor and outdoor environment.
