California Partners for Advanced Transportation Technology

This report describes the results of a one year effort to implement and analyze the performance of a Differ- ential Global Positioning System (DGPS) aided Inertial Navigation System (INS) for possible future use in Advanced Vehicle Control Systems (AVCS). The initial premise of this project was that DGPS/INS technology has the potential to serve as a centimeter-level position reference system as necessary for automated driving functions. Key advantages of this approach include: 1) no changes to the highway infrastructure are required; therefore, the DGPS/INS system should be less expensive to install and maintain than alternative reference systems; 2) knowledge of the DGPS position of a vehicle allows the use of significantly more path preview information than al- ternative position reference systems; therefore, control performance could be improved; 3) the navigation system would output the full vehicle state (position, velocity, and attitude) and inertial measurements at significantly higher rates than alternative navigation systems would provide even a subset of the vehicle state. The overall objective of this study was to implement a DGPS aided INS system and to analyze the technical feasibility of such a system relative to the requirements for vehicle control. The one year effort incorporated two main tasks: 1) Implementation of a real-time DGPS/INS; and, 2) Experimental analysis of the DGPS/INS performance. The DGPS/INS system provided estimates of vehicle position, linear velocities, and angular rates. State estimates are currently available at a rate of 100 Hertz, but significantly higher rates are feasible. Position accuracy at the centimeter level is achieved and demonstrated via two experiments. Integration of the DGPS aided INS into a control algorithm was not included in this one year study, but is one of the items discussed under future work. A few potential follow-on projects include: implementation of the DGPS/INS system in a control demon- stration, development and demonstration of more advanced (higher rates and increased accuracy) DGPS/INS systems, analysis of DGPS/INS systems with other sensor systems to achieve required system level relia- bility specifications, analysis of DGPS/INS AVCS protocols, and analysis of the need and performance of pseudolites in AHS systems. Specific detail regarding such efforts is included in the report conclusions. Keywords: Global Positioning System, Inertial Navigation, Differential Carrier Phase, Advanced Vehicle Control