GNSS Carrier Phase Improvement Using a MEMS INS-Aided Long Coherent Architecture for High Precision Navigation

The carrier phase measurements of the global navigation satellite system (GNSS) exhibit degraded accuracy and availability in challenging environments, thereby hindering their effective use for intelligent transportation applications. In this paper, an inertial navigation system (INS) aided GNSS signal tracking architecture with long coherent integration periods is proposed to provide accurate and continuous carrier phase observations in challenging environments. In order to implement efficient long coherent integration, a GNSS real time kinematic (RTK)/INS ultra-tight integration algorithm is designed to compensate for the dynamics induced by the receiver-satellite relative motion, and a multichannel cooperative loop with a specialized discriminator is proposed to eliminate the negative effects due to the receiver oscillator instability. Meanwhile, an accurate open loop tracking strategy is designed to sustain the integer ambiguity during a signal blockage, improving the continuity of the carrier phases. Initial blockage test shows that the open loop strategy can keep the carrier phase error below 90 degrees for over 40 seconds. Moreover, an INS based cumulative cycle slip decision variable (CCSDV) is proposed to detect the carrier phase cycle slips accurately. Finally, field vehicle tests were carried out using a (micro-electro-mechanical system) MEMS IMU. It turns out the proposed architecture significantly improves the accuracy and continuity of the carrier phase observations and it can provide superior positioning performance with a small amount of GNSS single frequency observations and a long RTK baseline.