Article
Design and Validation of a Cascading Vector Tracking Loop in
High Dynamic Environments
Zhiyong Tu, Yidong Lou * , Wenfei Guo , Weiwei Song and Yusheng Wang
Citation: Tu, Z.; Lou, Y.; Guo, W.;
Song, W.; Wang, Y. Design and
Validation of a Cascading Vector
Tracking Loop in High Dynamic
Environments. Remote Sens. 2021, 13,
2000. https://doi.org/10.3390/
rs13102000
Academic Editor: Kamil Krasuski
Received: 9 April 2021
Accepted: 14 May 2021
Published: 20 May 2021
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4.0/).
GNSS Research Center, Wuhan University, 129 Luoyu Road, Wuhan 430079, China;
2012301650022@whu.edu.cn (Z.T.); wf.guo@whu.edu.cn (W.G.); sww@whu.edu.cn (W.S.);
yushengwhu@whu.edu.cn (Y.W.)
* Correspondence: ydlou@whu.edu.cn; Tel.: +86-027-6877-7371
Abstract:
This paper designs a cascading vector tracking loop based on the Unscented Kalman
Filter (UKF) for high dynamic environment. Constant improvement in dynamic performance is
an enormous challenge to the traditional receiver. Due to the doppler effect, the satellite signals
received by these vehicles contain fast changing doppler frequency shifts and the first and second
derivatives of doppler frequency, which will directly cause a negative impact on the receiver’s stable
tracking of the signals. In order to guarantee the dynamic performance and the tracking accuracy,
this paper designs a vector carrier structure to estimate the doppler component of a signal. Firstly,
after the coherence integral, the IQ values are reorganized into new observations. Secondly, the phase
error and frequency of the carrier are estimated through the pre-filter. Then, the pseudorange and
carrier frequency are used as the observations of the main filter to estimate the motion state of the
aircraft. Finally, the current state is fed back to the carrier Numerical Controlled Oscillator (NCO)
as a complete closed loop. In the whole structure, the cascading vector loop replaces the original
carrier tracking loop, and the stable signal tracking of code loop is guaranteed by carrier assisted
pseudo-code method. In this paper, with the high dynamic signals generated by the GNSS signal
simulator, this designed algorithm is validated by a software receiver. The results show that this loop
has a wider dynamic tracking range and lower tracking error than the second-order frequency locked
loop assisted third-order phase locked loop in high dynamic circumstances. When the acceleration of
carrier is 100 g, the convergence time of vector structure is about 100 ms, and the carrier phase error
is lower than 0.6 mm.
Keywords:
cascading vector tracking; prefilter; high dynamic signal; software receiver; feedback loop
1. Introduction
Since the advent of the global positioning system (GPS), the global navigation satel-
lite system (GNSS) has become the most efficient technology for positioning. Normally,
according to some location solution methods, such as the Real Time Kinematic (RTK) or
the Precise Point Positioning (PPP), the accuracy of GNSS positioning is guaranteed, but
the upper limit of positioning accuracy is determined by the quality of signal tracking. In
some special circumstances (e.g., low signal to noise ratio or high dynamics), the GNSS
receiver has no tracking ability or low tracking quality, causing invalid positioning.
In 1998, NF Krasner [
1
] introduced the automatic frequency control (AFC) loop into
the GNSS receiver for locking carriers for better navigation signal tracking. The AFC
method tracks the carrier frequency by repeatedly adjusting a series of CNC oscillators
with simple structures and low accuracies [
2
]. In 1987, maximum likelihood estimation
(MLE) was used to track GPS signals [
3
], with high estimated frequency accuracy but a
complex structure [
4
]. Many estimation methods are being used in signal tracking, such
as fast Fourier transform [
5
] and adaptive least mean square [
6
]. However, the many
tracking methods are limited to the signal field, only utilizing a single channel to deal with
signal tracking.
Remote Sens. 2021, 13, 2000. https://doi.org/10.3390/rs13102000 https://www.mdpi.com/journal/remotesensing
