Article
An Improved Relative GNSS Tracking Method
Utilizing Single Frequency Receivers
Wenhao Yang, Yue Liu and Fanming Liu *
College of Automation, Harbin Engineering University, Harbin 150001, China;
irene_16317yang@hrbeu.edu.cn (W.Y.); liuyuehrb@outlook.com (Y.L.)
* Correspondence: hrblfm407@hrbeu.edu.cn; Tel.: +86-133-5198-3518
Received: 16 June 2020; Accepted: 20 July 2020; Published: 22 July 2020
Abstract:
The Global Navigation Satellite Systems (GNSS) becomes the primary choice for device
localization in outdoor situations. At the same time, many applications do not require precise absolute
Earth coordinates, but instead, inferring the geometric configuration information of the constituent
nodes in the system by relative positioning. The Real-Time Kinematic (RTK) technique shows its
efficiency and accuracy in calculating the relative position. However, when the cycle slips occur,
the RTK method may take a long time to obtain a fixed ambiguity value, and the positioning result
will be a “float” solution with a low meter accuracy. The novel method presented in this paper is
based on the Relative GNSS Tracking Algorithm (Regtrack). It calculates the changes in the relative
baseline between two receivers without an ambiguity estimation. The dead reckoning method is
used to give out the relative baseline solution while a parallel running Extended Kalman Filter (EKF)
method reinitiates the relative baseline when too many validation failures happen. We conducted
both static and kinematic tests to assess the performance of the new methodology. The experimental
results show that the proposed strategy can give accurate millimeter-scale solutions of relative motion
vectors in adjacent two epochs. The relative baseline solution can be sub-decimeter level with or
without the base station is holding static. In the meantime, when the initial tracking point and base
station coordinates are precisely obtained, the tracking result error can be only 40 cm away from the
ground truth after a 25 min drive test in an urban environment. The efficiency test shows that the
proposed method can be a real-time method, the time that calculates one epoch of measurement data
is no more than 80 ms and is less than 10 ms for best results. The novel method can be used as a more
robust and accurate ambiguity free tracking approach for outdoor applications.
Keywords:
ambiguity-free; differential GNSS relative positioning; dead reckoning; relative motion
solution; single-frequency receiver
1. Introduction
In recent years, novel opportunities are offered for low cost and highly accurate positioning owing
to the ability to share Global Navigation Satellite System (GNSS) measurement data between receivers,
coupled with the unique constraints of the GNSS positioning domain [
1
–
3
]. In outdoor applications,
such as autonomous driving, collision avoidance, land surveying, precision agriculture, and formation
flying of unmanned aerial vehicles (UAVs), the need to obtain a precise relative positioning instead of
an absolute positioning result by using GNSS is more prevalent [4,5].
In using the GNSS system for relative positioning, carrier phase is the most accurate measurement
method [
6
,
7
]. However, it is necessary to determine the ambiguity of the carrier phase measurement,
that is, to solve the ambiguity problem [
8
]. The least-squares ambiguity decorrelation adjustment
(lambda) is the best solution widely used at present thanks to its computational efficiency and supports
the decorrelation between estimated ambiguities [
9
,
10
]. Many applications and studies have used
Sensors 2020, 20, 4073; doi:10.3390/s20154073 www.mdpi.com/journal/sensors
