Simulation of GNSS/IMU Measurements

The IESSG has for many years been using simulators of various kinds in its research activities. There are many advantages of using simulators. Simulated data can provide early opportunities for the analysis of a potential measurement process. Simulators can enable a new computational technique to be assessed with controlled error budgets. For some years the IESSG has had a ‘GNSS’ simulator that enabled measurements to be generated and procedures and capabilities to be assessed. This has provided research opportunities that would not otherwise have been available. More recently the ‘GNSS simulator’ has been expanded to include the capability to simulate Inertial Measurement Unit (IMU) components (gyros, accelerometers) in an integrated environment. Detailed models of the performance of the inertial components have been developed, so that synthetic GNSS data and IMU data can be produced from a common platform. A trajectory generator allows synthetic data to be produced from a combined GNSS/IMU platform that is moving in a precisely controlled way. Data from this tool has been validated using an analysis filter from another source, as well as with in-house analysis tools. To date, these two tools have been used in a number of internal and contract research projects as well as being developed as a teaching tool. Of note is their use to simulate and assess the performance of future low-cost inertial components in an ESA-funded project entitled the 'Low-Cost Navigator'. They have also been used to develop an adaptive Kalman Filter, which integrates measurement data from GPS and inertial navigation sensor data. The aim of the filter is to optimise the blend of these two distinctly different types of measurements and make the best use of the synergy between them, to provide precise and reliable positioning. Recognising the strengths of the filter design, including its ability to work in a centralised or de-centralised mode, its ability to process carrier phase data, and its adaptive capabilities, the IESSG has recently begun a programme of development to produce a commercial version of the filter, suitable for embedding in bespoke hardware designs. The paper proposes to describe the simulator and filter, and will demonstrate the potential uses and application of these powerful tools.