Performance Analysis of an Ultra-Tightly Integrated GPS and Reduced IMU System

Ultra-tight GPS and inertial measurement unit (IMU) integration has been shown to provide improved tracking performance under weak signal conditions, during high vehicle dynamics and in the presence of jamming. However, for financially sensitive applications such as automobile navigation, the use of a full six degree of freedom IMU is impractical, even when using low cost MEMS-based devices. This paper therefore investigates using a reduced order IMU in an ultra-tight GPS/IMU receiver. Specifically, two horizontal accelerometers and one vertical gyro are considered. The paper presents the model used for the reduced IMU and the results of testing. Testing was done using live satellite signals and tactical-grade inertial sensors. Using a linear translation stage and a variable signal attenuator, the ultra-tight receiver is shown to provide about 5 dB of sensitivity improvement over a standard receiver implementation when evaluating the accuracy of the velocity solution. Furthermore, the velocity accuracy is found to be improved by about 60-90 % over the standard receiver and is approximately independent of signal attenuation.

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