Article
An Optimized Vector Tracking Architecture for Pseudo-Random
Pulsing CDMA Signals
Lin Tao, Guangchen Li , Junren Sun and Bocheng Zhu *
Citation: Tao, L.; Li, G.; Sun, J.; Zhu,
B. An Optimized Vector Tracking
Architecture for Pseudo-Random
Pulsing CDMA Signals. Sensors 2021,
21, 4087. https://doi.org/10.3390/
s21124087
Academic Editors: Kamil Krasuski
and Damian Wierzbicki
Received: 12 May 2021
Accepted: 7 June 2021
Published: 14 June 2021
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4.0/).
School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China;
taolin_yiran@pku.edu.cn (L.T.); liguangchen@pku.edu.cn (G.L.); sunjunren@pku.edu.cn (J.S.)
* Correspondence: zhubc@pku.edu.cn; Tel.: +86-139-1188-7720
Abstract:
The vector tracking loop (VTL) has high tracking accuracy and a superior ability to track
weak signals in GNSS. However, traditional VTL architecture is established on continuous Code
Division Multiple Access (CDMA) signal and is incompatible with pseudolite positioning systems
(PLPS) because PLPS generally adopts a pseudo-random pulsing CDMA signal structure to mitigate
the near-far effect. Therefore, this paper proposes an optimized VTL architecture for pseudo-random
pulsing CDMA signals. To avoid estimation biases in PLPS, the proposed VTL adopts irregular
update periods (IUP) pre-filters which adjust the update cycles according to the active timeslot
intervals. Meanwhile, as the active timeslots of different pseudolites do not overlap, the sampling
time of the navigation filter inputs is inconsistent and time-varying, causing jitter degradation. Thus,
the proposed VTL predicts the measurements so that they can be sampled at the same time, which
improves tracking accuracy. Simulation is carried out to evaluate the performance of the proposed
VTL. The results suggest that the proposed VTL outperforms the traditional pre-filter-based VTL and
IUP pre-filter-based VTL.
Keywords:
pseudo-random pulsing signal; irregular update periods; predicted mesurement; vector
tracking loop
1. Introduction
The Global Navigation Satellite System (GNSS) has been considered the first alterna-
tive to provide real-time positioning, navigation, and timing (PNT) services worldwide.
Despite the benefit of broad coverage, high accuracy, and low cost, the GNSS-based PNT
systems are fragile in challenging scenarios, such as deep valleys, heavily forested ar-
eas, open-cut mines, urban canyons, and even indoors [
1
,
2
]. Therefore, much research
has been carried out to improve GNSS availability and robustness in these challenging
environments [3,4].
The studies can be separated into two directions. One is to improve the
performance of GNSS systems [
3
], such as adopting more advanced signal structures [
5
,
6
],
applying anti-jamming receiving technologies [
7
], and enhancing signal power. The other is
to design new positioning systems suitable for the ground [
4
,
8
], such as
ultra-wideband [9],
Wi-FI [
10
], 4G or 5G [
11
], and pseudolite-based positioning technologies [
12
–
14
]. Due to
the benefits of the great flexibility, easy servicing, broad signals coverage, compatibility
with GNSS, and high positioning precision, the pseudolite positioning system has attracted
increasing attention in recent years.
Pseudolites are ground-based satellites transmitting GNSS-like signals. The posi-
tioning precision and continuity of the GNSS can effectively be improved by installing
pseudolites in urban areas, indoors, and in scenarios where the GNSS is problematic. Simul-
taneously, pseudolites can also be used to offer continuous and reliable positioning services
to users as an independent positioning system. However, the Pseudolites Positioning
Systems (PLPS) suffers severely from the near-far effect [
15
,
16
]. The near-field pseudolites
may interfere with far-field signals when the receiver moves close to a pseudolite, causing
Sensors 2021, 21, 4087. https://doi.org/10.3390/s21124087 https://www.mdpi.com/journal/sensors
