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In-orbit performance assessment of BeiDou intersatellite link ranging

September 2018
GPS Solutions 22(4)

Authors:

National University of Defense Technology

The introduction of an intersatellite link, also called a crosslink, is considered a promising technique for improving the reliability and integrity of a global navigation satellite system. As one of the most rapidly developing satellite navigation systems, the BeiDou system launched from March 2015 to February 2016 an in-orbit validation constellation that includes two inclined geosynchronous orbit satellites and three medium earth orbit satellites equipped with an intersatellite link in the Ka band. We modeled the intersatellite measurements of BeiDou and evaluated the ranging performance of the intersatellite link based on the analysis of in-orbit measurement data. We used both residual analysis and external data comparison to assess the data. The results show that the ranging precision of the BeiDou intersatellite link is within 10 cm and is determined mainly by the thermal noise of the receiver. Moreover, the drift rate of the group delay of the transceiver channel is within 1 cm per day.

Measurement scheme of the BeiDou ISL. In a link pair of 3 s, a satellite acts as a transmitter in one 1.5-s time slot and acts as a receiver in the other time slot. Satellites can establish an ISL with any visible satellite, and link pairs are reorganized every 3 s

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Differences between the Ka- and C-band measurements. The experiment was conducted in Xian in May 2015

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Architecture of the observation experiment. Laser and C-band ranging act as a reference to assess the performance of the Ka-band ISL. The Ka-band station is an anchor equipped with the same Ka-band ISL as the satellites

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Flowchart of the data comparison process. Data pre-processing is used to eliminate the influence of systematic error, such as atmospheric delay and relativistic effects. Data formalization refers to the process for obtaining the instantaneous distance from the raw measurement data considering the movement of satellites and the earth during the flight time of the signal. Data matching is the process used to find the corresponding laser observation data with the closest measurement time for each observation in the Ka-band measurement sequence. The unification of time and reference point is the process of correcting the data slightly according to the mathematical model to ensure that the ranging data used for comparison are synchronous and that the two endpoints of the ranging data are identical

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Fitting residuals (left) and their distribution (right) of measurements between I1S and M1S. The blue data in the top panel represent the pseudorange transmitted from M1S to I1S, the green data in the middle panel represent the pseudorange transmitted from I1S to M1S, and the red data in the bottom panel represent the pseudorange of the dual one-way ranging. The residuals are clearly within 0.3 m, and the distributions of the residuals are approximately normal distributions

…

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GPS Solutions (2018) 22:119

https://doi.org/10.1007/s10291-018-0784-0

ORIGINAL ARTICLE

In-orbit performance assessment ofBeiDou intersatellite link ranging

YifanZhou1· YuekeWang1· WendeHuang1 · JunYang1· LeyuanSun1

Received: 9 October 2017 / Accepted: 11 September 2018 / Published online: 17 September 2018

Abstract

The introduction of an intersatellite link, also called a crosslink, is considered a promising technique for improving the reli-

ability and integrity of a global navigation satellite system. As one of the most rapidly developing satellite navigation systems,

the BeiDou system launched from March 2015 to February 2016 an in-orbit validation constellation that includes two inclined

geosynchronous orbit satellites and three medium earth orbit satellites equipped with an intersatellite link in the Ka band. We

modeled the intersatellite measurements of BeiDou and evaluated the ranging performance of the intersatellite link based on

the analysis of in-orbit measurement data. We used both residual analysis and external data comparison to assess the data.

The results show that the ranging precision of the BeiDou intersatellite link is within 10cm and is determined mainly by the

thermal noise of the receiver. Moreover, the drift rate of the group delay of the transceiver channel is within 1cm per day.

Keywords Intersatellite link· Ranging performance· BeiDou· Ka band

Introduction

The intersatellite link (ISL) is an important part of a modern

global navigation satellite system (GNSS). With the support

of intersatellite measurements and communication, a GNSS

can achieve autonomous navigation to eﬀectively reduce the

number of ground stations and maintenance costs, shorten

the ephemeris update cycle, and improve navigation per-

formance. The system can run independently even if the

ground stations are oﬄine or destroyed, which can signiﬁ-

cantly enhance the lifetime of the system during times of

external threats.

The global positioning system (GPS) planned to develop

its ISL at a very early stage to transfer nuclear detonation

detection system data together with autonomous navigation

and ranging data between Block II, Block IIA and Block

IIR GPS space vehicles (SVs) within radio frequency (RF)

view of each other (Sonntag 1997). For the Block IIR GPS

satellites, an ISL operating on the ultrahigh-frequency band

was designed to enhance the service performance. This

ISL adopts a frequency-hopping spread-spectrum system

combined with a time division multiple access (TDMA)

scheme (Xu etal. 2012). The pseudorange measurements

of the ISL are used by the onboard computers to update

the stored navigation messages, including the ephemeris

and clock states (Abusali etal. 1998). The ISL of the Block

IIR GPS satellites was tested in orbit in 2001. Performance

results from in-orbit ranging tests indicate that autonomous

navigation operation of the Block IIR GPS satellites is

achievable after proper measurement calibration techniques

are applied (Rajan etal. 2003). Plans for intersatellite links

on GPS III are currently unclear.

The European Space Agency (ESA) assessed certain

exploratory projects within the General Studies Programme

(GSP) to analyze what potential improvements to a GNSS

system could be achieved by introducing intersatellite rang-

ing and intersatellite communication links (Fernández

2011). The application of optical quantum communication

links to a GNSS network, with reference to the Galileo archi-

tecture, was discussed in Gerlin etal. (2013). Although the

ISL of Galileo remains in the planning stage, the replace-

ment of the satellites will give the opportunity to install an

ISL in the 2020s (ESA 2012).

The Russia GLONASS has augmented new-generation

satellites with an S-band crosslink (Lin etal. 2010). Fur-

thermore, the ﬁrst GLONASS K satellite with a laser ISL

was launched in February 2011, and an intersatellite laser

* Wende Huang

nn_hwd@126.com

1 College ofMechatronics Engineering andAutomation,

National University ofDefense Technology, No. 109, Deya

Road, Changsha410073, China

Content courtesy of Springer Nature, terms of use apply. Rights reserved.

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