Low-latency, high-rate, high-precision relative positioning with moving base in real time

Abstract

Relative positioning with a moving base is required in many vehicle-to-vehicle applications. Due to unavoidable latency, conventional synchronous real-time kinematic (SRTK) positioning, which refers a fixed base, cannot fulfill the requirements of high-speed safety–critical situations since the movement of the base during the latency must be considered. We present an asynchronous RTK (ARTK)/time-differenced carrier phase (TDCP) integration method. We first introduce the ARTK method to directly obtain the asynchronous baseline between moving base and rover at their respective observation epochs. The position increments of the moving base during the latency are then calculated by the TDCP technique. Finally, the two positioning results are combined to achieve low-latency, high-rate, and high-precision relative positioning. With the proposed method, the size of transmitted data packets can be significantly reduced, which is beneficial for real-time implementation. It is also noted that the proposed method can be easily merged with global navigation satellite system/inertial navigation system (INS) integration to further improve the output rate of relative position. The performance is evaluated by a field test using two moving vehicles with one being the moving base and the other the rover. Results show that the baseline error is less than 1 cm compared to reliably post-processed SRTK results when latencies of raw observations remain below 1 s. Even when the latency is 15 s, centimeter-level accuracy can still be guaranteed. With ARTK/TDCP/INS integration, decimeter-to-centimeter-level higher-rate (> 100 Hz) relative positioning results can be obtained.