A New MIMU/GNSS Ultra-Tightly Coupled Integration Architecture for Mitigating Abrupt Changes of Frequency Tracking Errors.

Shiming Liu,Feng Wu,Qiangwen Fu,Yuanbo Tao,Sihai Li

doi:10.3390/mi11121117

Shiming Liu, Feng Wu + Show 3 more

Open Access

https://doi.org/10.3390/mi11121117

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Abstract

We present a new ultra-tightly coupled (UTC) integration architecture of a micro-electromechanical inertial measurement unit (MIMU) and global navigation satellite system (GNSS) to reduce the performance degradation caused by abrupt changes of frequency tracking errors. A large frequency error will lead to a decrease in the carrier-to-noise ratio (C/N0) estimate and an increase in the code discriminator estimation error. The disruptive effects of frequency errors on the estimation of C/N0 and on the code discriminator are quantitatively evaluated via theoretical analyses and Monte Carlo simulations. The new MIMU/GNSS UTC architecture introduces a large frequency error detector and a refined frequency processor based on a retuned frequency in each tracking channel. In addition, an adaptive channel prefilter with multiple fading factors is introduced as an alternate to the conventional prefilter. Numerical simulations based on a highly dynamic trajectory are used to assess performance. The simulation results show that when there is an abrupt step change in the frequency tracking error, the new UTC architecture can effectively suppress the divergence of navigation solutions and the loss of tracking lock, and can significantly reduce the deviation of the C/N0 estimation.

Highlights

An inertial navigation system (INS) can be combined with multiple navigation technologies to form an integrated navigation system
We present an enhanced micro-electromechanical inertial measurement unit (MIMU)/global navigation satellite system (GNSS) ultra-tightly coupled (UTC) integration system to mitigate performance degradation caused by abrupt changes in frequency tracking errors
Simulation experiment results are presented to evaluate the performance of the enhanced UTC (EUTC) integration system in the presence of large frequency errors

Summary

Introduction

An inertial navigation system (INS) can be combined with multiple navigation technologies to form an integrated navigation system. In the context of MIMU/GNSS UTC integration, there are two main reasons for the large jumps in frequency tracking errors. Large frequency tracking errors will cause the attenuation of coherent integration values. They cause a sudden decrease in the estimated carrier-to-noise ratio (C/N0) and an increase in the code tracking error. When the oscillator frequency jumps significantly, the apparent C/N0 will suddenly drop for all tracking channels [9] For this reason, the estimated C/N0 is used as an indicator to detect large frequency errors in [9]. We present an enhanced MIMU/GNSS UTC integration system to mitigate performance degradation caused by abrupt changes in frequency tracking errors. Where c/n0 is the carrier-to-noise ratio in Hz

Integration Kalman Filter

Quantitative Analyses of Disruptive Effects of Large Frequency Errors

Effffects on the Code TrraacckkiinnggEErrrroorrEEssttiimmaattiioonn

Adaptive Prefilter with Multiple Fading Factors

Simulation Setup

Conclusions