optimizing gnss signals’ tracking under strong ionospheric ... · tao lin, gérard lachapelle...
TRANSCRIPT
Optimizing GNSS signals’ tracking under
strong ionospheric scintillation in Brazil
using the CIGALA network, baseband data
and a software receiver
Workshop CALIBRA DAY, São Paulo, May 9, 2014
Luiz Paulo Souto Fortes IBGE/UERJ – Brazil
Scholar of CNPq
Tao Lin, Gérard Lachapelle University of Calgary - Canada
Contents
Introduction
• The 2013 Solar Maximum and its effects on GNSS signals
• Research objectives
Data collection and processing
Results in the observation and position domains
GSNRx™ features for tracking under scintillation
Conclusions
The
Solar
Cycles
The Solar Cycle 24
• Ionospheric delay
– Dependent on signal
frequency and level of
ionization (i.e., TEC)
Effects on GNSS signals
• Ionospheric scintillation
– Random rapid variations in the intensity and phase of the
received signals resulting from electron density irregularities in
the ionosphere
• CORS network
operated by IBGE
• 101 stations
(March 2014)
• Provide access to
SIRGAS2000
• More than 40,000
downloads per
month!
• To investigate the effects of the 2013 Solar Maximum on GNSS signals’ tracking, using:
– Baseband (i.e., Intermediate Frequency - IF) data collected by a front-end device at IBGE facilities in Rio de Janeiro
– GSNRx™ software receiver developed by the Position, Location and Navigation (PLAN) Group of the Department of Geomatics Engineering, University of Calgary, Canada
• To contribute to the development of robust GNSS signals’ tracking methods
• To study software receivers in order to evaluate their use in RBMC
Research objectives
GNSS Software receiver
Preamplifier Down
Converter IF Sampling
Reference
Oscillator
Frequency
Synthesizer
IF Signal
Processing
Navigation
Processing
Antenna
Local Oscillator
RF Front-End Signal Processing
Advantage of using a software receiver:
the flexibility of a software-based approach
Hardware
Software
• Baseband (IF) data collected from June 04 2012 to
March 29 2013, 8-12pm local time
– Suitable time period, as the peak of Solar Cycle 24 occurred in
September 2013, with a secondary peak in February 2012
Data collection
Data collection
RIOFE station (front-
end) located 5m from
RBMC RIOD station,
allowing performance
comparison
• 4-hour IF data file: 67GB (compressed!)
• Challenge: very difficult to predict scintillation
Data collection
Automaticaly
collect IF data
Check the CIGALA
website
Scintillation
occurence? Save the file
Yes Delete the file
No
Methodology
79 data files collected, 5.16TB in total!
Data collection
• 5 sessions selected for processing
– October 24 2012, November 17 2012, February 20 2013: under severe equatorial ionospheric scintillation
– March 28 2013: few satellites affected by scintillation
– June 04-05 2012: no scintillation, for comparison
Data processing
Amplitude scintillation S4 index
CIGALA SJCU station
Data processing
Data processing
Amplitude scintillation S4 index
CIGALA SJCU station
Data processing
Amplitude scintillation S4 index
CIGALA SJCU station
Data processing
Amplitude scintillation S4 index
CIGALA SJCU station
Data processing
Amplitude scintillation S4 index
CIGALA SJCU station
• Decompressing the 67GB session file
– Generates 2 files (for L1 and L2) with
268GB each
– At the beginning, this process took 8 hours;
with computer hardware improvements, the
processing time was reduced to 1h40m
• Processing the L1 and L2 session files
with GSNRx™
– At the beginning, it took around 29 hours;
with computer hardware and software
improvements, this time was reduced to
5 to 7 hours
Data processing
The final processing time of a 4-hour IF session file:
7 to 9h
• S4 computation using in-phase (I) and quadra-
phase (Q) accumulation results of the channel
correlators generated by GSNRx™
(SI = signal intensity)
Data processing
2
22
SI
SISIS4
Data processing S4 at RIOFE vs SJCU (350 km apart)
S4 vs C/No for PRN12 L1 C/A and L2CM signals
Data processing
Results in the observation domain
• Analysis of the GSNRx™ and RIOD Trimble NetRS
observations under ionospheric scintillation
– Cycle slip detection using the dual frequency method
– Missing GPS L2 phase observations,
for IIR-M e IIF satellites, as the GSNRx™ version
used in this research operated on L1 and L2C
signals (and not on L2P(Y))
thresholdΦΦΦΦ12 tL2L1tL2L1
Results in the observation domain
Satellites (SV)
IIR-M/IIF
Missing L2
observations (%)
# of dual frequency
cycle slips
RIOFE RIOD RIOFE RIOD
05 16 17 0 22
12 0 5 0 47
15 2 20 0 23
25 0 1 0 3
29 1 18 0 60
31 3 22 0 27
Total for IIR-M
and IIF SV 4 11 0 182
Total for all
visible SV -- 13 -- 288
Session: October 24, 2012
(strong scintillation)
Session: November 17, 2012
(strong scintillation)
Satellites (SV)
IIR-M/IIF
Missing L2
observations (%)
# of dual frequency
cycle slips
RIOFE RIOD RIOFE RIOD
05 1 4 0 19
12 5 4 0 38
15 25 52 0 0
25 0 0 0 5
29 0 0 2 0
31 0 0 0 0
Total for IIR-M
and IIF SV 3 4 2 62
Total for all
visible SV -- 9 -- 146
Results in the observation domain
Session: February 20, 2013
(strong scintillation)
Satellites (SV)
IIR-M/IIF
Missing L2
observations (%)
# of dual frequency
cycle slips
RIOFE RIOD RIOFE RIOD
01 0 5 0 2
31 7 8 0 2
Total for IIR-M
and IIF SV 4 7 0 4
Total for all
visible SV -- 8 -- 167
Results in the observation domain
Session: March 28, 2013
(strong scintillation on fewer SV)
Satellites (SV)
IIR-M/IIF
Missing L2
observations (%)
# of dual frequency
cycle slips
RIOFE RIOD RIOFE RIOD
01 0 0 0 0
07 14 27 0 0
31 0 0 0 0
Total for IIR-M
and IIF SV 1 2 0 0
Total for all
visible SV -- 5 -- 23
Results in the observation domain
Satellites (SV)
IIR-M/IIF
Missing L2
observations (%)
# of dual frequency
cycle slips
RIOFE RIOD RIOFE RIOD
05 0 0 0 0
07 0 0 0 0
17 0 8 0 0
Total for IIR-M
and IIF SV 0 2 0 0
Total for all
visible SV -- 6 -- 0
Session: June 04-05, 2012
(no scintillation)
Results in the observation domain
RBMC receiver evolution since the previous Solar
maximum (2002)
Missing L2 observations (%) # of dual frequency cycle slips
RIOD – Trimble SSi – March 17 2002 (S4 0,95)
41 89
RIOD – Trimble NetRS – October 24 2012
13 288
UBA1 – Trimble NetR8 – October 24 2012 (200 km from RIOD)
7 125
RIOFE – GSNRx – October 24 2012 (5 m from RIOD)
(for IIR-M and IIF satellites only)
4 0
Results in the observation domain
Results in the position domain
• Analysis of PPP positioning using GSNRx™ and RIOD
Trimble NetRS observations under ionopsheric
scintillation
– PPP services used:
• IBGE
• Natural Resources Canada (NRCan)
– Final results with NRCan-PPP
• L1 pseudorange kinematic solutions for the 5 selected days
• Code+phase dual frequency kinematic solutions require
enough epochs with L1, L2, C1 and C2/P2 observations for
4 to 5 satellites condition fulfilled on November 17, 2012
Results in the position domain
NRCan-PPP L1 pseudorange kinematic solutions
NRCan-PPP L1 pseudorange kinematic solutions
Results in the position domain
NRCan-PPP L1 pseudorange kinematic solutions
Results in the position domain
NRCan-PPP L1 pseudorange kinematic solutions
Results in the position domain
NRCan-PPP L1 pseudorange kinematic solutions
Results in the position domain
Results in the position domain
Results in the position domain
NRCan-PPP dual frequency (= iono.free) kinematic solutions
Results in the position domain
Station Type of PPP
Solution
Differences to known coordinates (m) A posteriori code std deviation
(m)
Latitude Longitude Height
RMS Mean RMS Mean RMS Mean
Session: October 24 2012 (strong scintillation) RIOFE L1 code 3,9 -2,1 3,8 3,1 7,9 -1,6 2,8
RIOD L1 code 4,2 -2,3 4,0 3,2 6,9 -1,3 2,9
Session: November 17 2012 (strong scintillation) RIOFE L1 code 3,2 -1,5 2,8 1,5 4,3 1,4 2,6
RIOD L1 code 3,3 -1,7 3,1 2,0 4,2 1,5 2,4
RIOFE
L1 L2 code (C/A and L2C)
and phase 0,16 0,15 0,07 -0,05 0,33 0,25 2,8
RIOD
L1 L2 code (C/A and L2P)
and phase 0,24 0,03 0,13 0,06 0,12 0,01 1,1
Session: February 20 2013 (strong scintillation) RIOFE L1 code 2,5 -1,6 2,2 1,8 3,8 2,1 2,1
RIOD L1 code 2,6 -1,6 2,1 1,7 4,2 2,2 2,0
Session: March 28 2013 (strong scintillation on fewer satellites) RIOFE L1 code 4,6 -3,6 2,0 1,3 8,1 5,8 2,2
RIOD L1 code 4,8 -3,8 1,8 1,4 8,2 5,8 2,0
Session: June 04-05 2012 (no scintillation) RIOFE L1 code 0,7 0,2 0,8 -0,4 1,9 -0,3 0,9
RIOD L1 code 0,4 0,2 0,3 -0,1 0,9 -0,2 0,5
Results in the position domain
GSNRx™ features for tracking under scintillation
• Data collected represented important and excellent sample to optimize tracking under scintillation
• Main features implemented on GSNRx™ – Tracking parameters
• Phase Lock Loop bandwith reduced from 15 to 3 Hz
• Delay Lock Loop bandwith reduced from 2.5 to 0,01 Hz
– Receiver architecture:
• From independent-channel architecture to shared-channel architecture, which utilizes the inter-channel aiding from channels and satellites for robust GNSS signal tracking under scintillation
• Results shown in this presentation have been generated using GSNRx™ optimized version
Conclusions
• Collection of important and unseen 5.16TB IF dataset
for GNSS signal acquisition and tracking research
• Evolution of RBMC geodetic receivers during the past
11 years, reducing the missing GPS L2 observations
by a factor of 3 to 6 improvement of the information
made available to users
• GSNRx™ flexibility has allowed optimizing acquisition
and tracking of GPS signals under severe scintillation
excellent performance, superior to RBMC receivers,
with only 4% of missing L2 observations and ZERO
cycle slips in all scenarios
Conclusions
• Current GNSS signals acquisition and tracking algorithms
are highly resistant to equatorial ionospheric scintillation
• Submission of GSNRx™ and Trimble NetRS observations to
the NRCan-PPP service generated similar results in the
position domain, with ionospheric delay being responsible
for degrading the coordinates’ accuracy by a factor up to 12
• The flexibility and potential of a software receiver justify the
need of closely following up the corresponding
technology/cost evolution in order to assess its use in
RBMC
Acknowledgements
• Mark Petovello, Fatemeh Ghafoori and James Curran, PLAN
Group of the Department of Geomatics Engineering, University of
Calgary
• Maria Cristina Barboza Lobianco, Sonia Maria Alves Costa,
Rodrigo Augusto Quirino e Alberto Luis da Silva, Coordination of
Geodesy - IBGE Directorate of Geosciences
• Mario Luiz Souto, Coordination of Technology - IBGE Directorate of
Information Technology
• Pierre Tétreault and the team responsible for the NRCan-PPP
service
• João Francisco Galera Monico, CIGALA and Unesp