Article
Design and Implementation of Vector Tracking Loop for
High-Dynamic GNSS Receiver
Rongjun Mu and Teng Long *
Citation: Mu, R.; Long, T. Design
and Implementation of Vector
Tracking Loop for High-Dynamic
GNSS Receiver. Sensors 2021, 21, 5629.
https://doi.org/10.3390/s21165629
Academic Editors: Kamil Krasuski
and Chris Rizos
Received: 19 June 2021
Accepted: 18 August 2021
Published: 20 August 2021
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School of Astronautics, Harbin Institute of Technology, Harbin 150001, China; murjun@163.com
* Correspondence: 16B918074@stu.hit.edu.cn
Abstract:
For the tracking of high-dynamic satellite navigation signals, the conventional scalar
tracking loop (STL) is vulnerable. Frequent signal-tracking interruption affects the continuity of
navigation. The vector tracking loop (VTL) can overcome this disadvantage. However, there are
some difficulties in implementing existing vector tracking methods on a real-time hardware receiver,
such as the synchronization problem and computation load. This paper proposes an implementation
framework of VTL based on a partial open-loop numerically controlled oscillator (NCO) control
mode that can be implemented with minor modifications on an existing receiver platform. The
structure of VTL, the design of the navigation filter, and the key points of hardware implementation
are introduced in detail. Lastly, the VTL performance was verified by a GPS simulator test. The
results show that the proposed VTL can run in real-time and be significantly improved in the tracking
continuity of high-dynamic signals, tracking sensitivity, positioning accuracy, and recovery time for
interrupted signals compared with those of STL.
Keywords: GNSS; vector tracking; high-dynamic; hardware receiver
1. Introduction
Global navigation satellite systems (GNSS) are widely used in positioning and naviga-
tion tasks for artificial flight vehicles as a high-availability, high-precision, and low-cost
positioning technology. Some of these vehicles have high velocity and acceleration, such
as missiles, rockets, and hypersonic aircraft. This requires the GNSS receiver to have the
ability to track high-dynamic signals. As early as 1988, the Jet Propulsion Laboratory (JPL)
researched high-dynamic global positioning system (GPS) signal tracking according to the
application requirement of the GPS Range Application Joint Program Office (RAJPO) [
1
].
In that report, a scenario with an acceleration of 50 g and a jerk of 100 g/s was proposed as
the upper bound for the study of high-dynamic signal tracking.
There are three main factors affecting the high-dynamic performance of a receiver:
Loop filter characteristics, oscillator noise, and oscillator vibration sensitivity [
2
]. The latter
two can be improved on the hardware-design level [
3
], but the first needs to be improved
on the software and algorithmic levels, which are the focus of this paper. There are many
proposed methods on how to achieve high-dynamic signal tracking, such as second-order
frequency lock loop (FLL) assisted third-order phase lock loop (PLL) [
4
], Kalman filter-
based [
5
], maximum likelihood-based [
6
], and fractional Fourier transform-based [
7
,
8
].
However, these methods focus only on a single channel and ignore overall performance.
Subject to the nature of scalar tracking loop (STL) in which signal-tracking channels are
independent of each other, the optimization of one channel cannot optimize the receiver.
Some channels may still lose the lock when a high-dynamic or weak signal is encountered.
The problem of the continuity of signal tracking has not been solved. Fortunately, the
vector tracking loop (VTL) was proposed to overcome the disadvantage of STL [
9
]. The
principle of VTL is to combine the signal tracking of all channels via the receiver’s position,
velocity, and time (PVT) solution, which gives several advantages. First, information fusion
Sensors 2021, 21, 5629. https://doi.org/10.3390/s21165629 https://www.mdpi.com/journal/sensors
