Integrated GPS/INS systems provide an enhanced navigation system that has superior performance in comparison with either system operating in stand-alone mode as it can overcome each of their limitations. The high cost and government regulations prevent the wider inclusion of high quality IMUs to augment GPS as a commercialized navigation system in many navigation applications. The progress in MEMS technology enables complete inertial units on a chip, composed of multiple integrated MEMS accelerometers and gyroscopes. In addition to their compact and portable size, the price of MEMS based is far less than those high quality IMUs as well, however, due to the lightweight and fabrication process, MEMS sensors have large bias instability and noise, which consequently affect the obtained accuracy from MEMS-based IMUs. Many research works have been conducted to improve the performance of low cost MEMS-based INS/GPS integrated systems. Accommodating heading measurements update using physical heading sensors (e. g. GPS heading sensors and magnetic compass) or pseudo heading sensor (e. g. derived from GPS velocities or positions) is an appropriate option to solve the problem. In this study, three approachs are implemented to obtain the headings of a moving vehicle using carrier phase DGPS measurement. Then a 21 states loosely-coupled extended Kalman filter is applied to integrate a low cost GPS/MEMS system along with the heading updates provided by the heading sensor to examine the positioning accuracy of proposed system.
