GNSS/INS integration in vehicular urban navigation

In critical locations as urban or mountainous areas satellite navigation is difficult, above all due to the signal blocking problem; for this reason satellite systems are often integrated with inertial sensors, owing to their complementary features. A common configuration includes GPS receiver and an high-precision inertial sensor, able to provide navigation information during GPS gaps. Nowadays the low cost inertial sensors with small size and weight and poor accuracy are developing and their use as part of integrated navigation system in difficult environments is under investigation. On the other hand the recent enhancement of GLONASS satellite system suggests the combined use with GPS in order to increase the satellite availability; this can be especially useful in places with lack of GPS signals. This study purpose is to assess the effectiveness of the integration of GPS/GLONASS with low cost inertial sensors in vehicular urban navigation The Extended Kalman filter is used to merge the satellite and inertial information and the loosely and tightly coupled architectures are the integration strategies adopted; their performances comparison in difficult areas is one of the main purpose. Generally the tight coupling is more used in urban or natural canyons because it can provide an integrated navigation solution also with less than four satellites (minimum number of satellites necessary for a GPS only positioning); the inclusion of GLONASS satellites in this context may change significantly the role of loosely coupling in urban navigation. In this work pseudorange and Doppler measurements are processed in single point mode; hence no differential processing is performed and no base station is necessary.