Monitoring and Assessment
Parameters on GNSS
Draft
September,2012
Contents
1 Scope ........................................................................................................................... 1
2 GNSS Monitoring and Assessment Parameters .......................................................... 1
2.1 Constellation Status ........................................................................................... 1
2.1.1 Satellite Operational status ............................................................................... 1
2.1.2 Orbit Parameters............................................................................................... 1
2.1.3 DOP .................................................................................................................. 1
2.2 Navigation Signal............................................................................................... 2
2.2.1 User-Received Signal Level ............................................................................. 2
2.2.2 Power Spectrum ............................................................................................... 2
2.2.3 Ranging Code Waveform in the Time Domain ................................................ 2
2.2.4 Modulation Error.............................................................................................. 2
2.2.5 Correlation Characteristics ............................................................................... 3
2.3 Navigation Message ........................................................................................... 4
2.3.1 Navigation Message Status .............................................................................. 4
2.3.2 Orbit Accuracy of Broadcast Ephemeris .......................................................... 4
2.3.3 Clock Offset Accuracy of Broadcast Ephemeris .............................................. 4
2.3.4 Signal-In-Space User Ranging Error (SIS URE) ............................................. 4
2.3.5 Signal-In-Space Continuity .............................................................................. 4
2.3.6 Signal-In-Space Availability............................................................................. 5
2.3.7 Signal-In-Space Missed Alarm Rate ................................................................ 5
2.3.8 User Ranging Rate Error (URRE) .................................................................... 5
2.3.9 User Ranging Acceleration Error ( URAE ) ..................................................... 5
2.3.10 Broadcast Ionospheric Delay Model Accuracy .............................................. 5
2.3.11 TGD Accuracy................................................................................................ 6
2.3.12 Inter-System Bias (ISB) Accuracy ................................................................. 6
2.3.13 System Time Performance ............................................................................. 6
2.3.14 UTC Offset Error (UTCOE)........................................................................... 6
2.3.15 Coordinate Transformation Parameters .......................................................... 7
2.4 Service Performance .......................................................................................... 7
2.4.1 Position, Velocity and Timing (PVT) Accuracy ............................................... 7
2.4.2 Continuity......................................................................................................... 7
2.4.3 Availability ....................................................................................................... 7
2.4.4 Integrity ............................................................................................................ 8
3 References ................................................................................................................... 1
Appendix ........................................................................................................................ 3
I
1 Scope
This document is mainly aimed to propose GNSS monitoring and
assessment parameters through elaborating their definitions and functions,
which can be applied to the monitoring and assessment of international
GNSS Open Services.
2 GNSS Monitoring and Assessment Parameters
2.1 Constellation Status
2.1.1 Satellite Operational status
1) Definition: The total number of satellites currently in service and
the healthy state of each satellite.
2) Function: Basic criterion for marking the availability of satellites.
2.1.2 Orbit Parameters
1) Definition: Ephemeris parameters for describing satellite position
and velocity.
2) Function: To monitor spatial distribution of the constellation.
2.1.3 DOP
1) Definition: Dilution of precision, including GDOP, PDOP, TDOP,
HDOP and VDOP, describes the spatial geometric distribution
between the visible satellites and users. .
1
2) Function: To Monitor and evaluate the performance of
constellation configuration.
2.2 Navigation Signal
2.2.1 User-Received Signal Level
1) Definition: User-received power of satellite navigation signal.
2) Function: To Monitor and evaluate strength and variation range
of the received signal on the ground
2.2.2 Power Spectrum
1) Definition: Power distribution of navigation signals in the
frequency domain.
2) Function: To Monitor and evaluate the amplitude and frequency
distortion of navigation signals.
2.2.3 Ranging Code Waveform in the Time Domain
1) Definition: Ranging code amplitude variation over time.
2) Function: To monitor and evaluate waveform distortion of the
ranging code in the time domain.
2.2.4 Modulation Error
1) Definition: Errors generated in the process of navigation signal
modulation and transmission, mainly including phase modulation error
and amplitude modulation error.
2
(1) Phase modulation error: Phase difference between the received
and ideal navigation signals of each channel.
(2) Amplitude modulation error: Amplitude difference between the
received and ideal navigation signals of each channel.
2) Function: To monitor and evaluate phase and amplitude
distortion generated in the process of navigation signal modulation and
transmission.
2.2.5 Correlation Characteristics
1) Definition: Outputs of correlation peak amplitude and correlation
curve characteristics after the operation of signal correlation.
The amplitude and waveform features of the output correlation peak
of the signal after correlation calculation.
(1) Correlation loss: Power difference between the actually
received signal and the ideal signal in the designed bandwidth of the
signal.
(2) Correlation curve: The curve obtained through correlation
calculation between recovered ranging code and the ideal ranging code of
all signals
2) Function: To evaluate amplitude attenuation of the correlation
output and distortion of the correlation curve caused by waveform
distortion of the signal chip.
3
2.3 Navigation Message
2.3.1 Navigation Message Status
1 ） Definition: The consistency and rationality between the
navigation message and ICD specifications.
2）Function: To evaluate the state of the navigation message.
2.3.2 Orbit Accuracy of Broadcast Ephemeris
1）Definition: Statistics of orbit difference between the broadcast
ephemeris and precise ephemeris.
2）Function: To evaluate orbit accuracy of the broadcast ephemeris.
2.3.3 Clock Offset Accuracy of Broadcast Ephemeris
1）Definition: Statistics of clock offset difference between the
broadcast ephemeris and precise ephemeris.
2）Function: To evaluate clock offset accuracy of broadcast
ephemeris.
2.3.4 Signal-In-Space User Ranging Error (SIS URE)
1）Definition: The user's line-of-sight error caused by broadcast
ephemeris error.
2）Function: To evaluate the accuracy of Signal-In-Space.
2.3.5 Signal-In-Space Continuity
1 ） Definition: The probability that URE doesn’t exceed the
4
threshold without interruption over a specified time interval.
2）Function: To evaluate the continuity of Signal-In-Space.
2.3.6 Signal-In-Space Availability
1 ） Definition: The probability that URE doesn’t exceed the
threshold over a specified time interval.
2）Function: To evaluate the availability of Signal-In-Space.
2.3.7 Signal-In-Space Missed Alarm Rate
1）Definition: The probability that no alarming issued when SIS
URE exceeds the threshold.
2）Function: To monitor and evaluate the integrity of
Signal-In-Space.
2.3.8 User Ranging Rate Error (URRE)
1）Definition: The first-order derivative of URE versus time.
2）Function: To describe the changing rate of URE.
2.3.9 User Ranging Acceleration Error ( URAE )
1）Definition: The second-order derivative of time versus URE.
2）Function: To describe the change rate of URRE.
2.3.10 Broadcast Ionospheric Delay Model Accuracy
1）Definition: Statistical difference between the broadcast and real
ionospheric correction.
5
2）Function: To evaluate accuracy of the broadcast ionospheric
delay.
2.3.11 TGD Accuracy
1）Definition: The accuracy of Group Delay Time （TGD）
parameters in broadcast ephemeris.
2）Function: To evaluate the accuracy and stability of TGD
parameters in broadcast ephemeris.
2.3.12 Inter-System Bias (ISB) Accuracy
1）Definition: The system time bias and its accuracy among different
satellite navigation systems.
2）Function: To evaluate the accuracy of time bias among satellite
navigation systems.
2.3.13 System Time Performance
1）Definition: The performance of system time of satellite
navigation systems, usually including accuracy and stability.
2）Function: To evaluate the time performance of each satellite
navigation system.
2.3.14 UTC Offset Error (UTCOE)
1）Definition: The offset error between system time of satellite
navigation systems and UTC.
6
2）Function: To evaluate the system time performance of satellite
navigation systems.
2.3.15 Coordinate Transformation Parameters
1）Definition: The transformation relations among the coordinate
system of different satellite navigation systems.
2）Function: To monitor coordinate datum transformation relations
among different satellite navigation systems.
2.4 Service Performance
2.4.1 Position, Velocity and Timing (PVT) Accuracy
1) Definition: The actually achieve PVT accuracy by users.
2) Function: To serve as service reference for users.
2.4.2 Continuity
1) Definition: The capability of a satellite navigation system to
provide continuous services within certain time period and service area.
2) Function: To evaluate the continuity of system service.
2.4.3 Availability
1) Definition: The percentage of time that the navigation system is
able to provide nominal accuracy within its service area.
2) Function: To evaluate the availability of system service.
7
2.4.4 Integrity
1) Definition: The capability to issue timely alerts when the system
performance cannot meet nominal indicators.
2) Function: To evaluate the integrity of system service.
8
3 References
[1] Global Positioning System Standard Positioning Service Performance
Standard, Version 4, September 2008.
[2] GPS Civil Monitoring Performance Specification, April 2009.
[3] European GNSS (Galileo) Open Service Signal In Space Interface
Control Document (OS SIS ICD) Issue 1.1, October 2010.
[4] Global Navigation Satellite System (GLONASS) Interface Control
Document, Version 5.1, 2008.
[5] IS-GPS-200E (Navstar GPS Space Segment/ Navigation User
Interfaces), August 2010.
[6] ICD-GPS-240A (Navstar GPS Control Segment to User Support
CommunityInterfaces), October 2010.
[7] IS-GPS-705A (Navstar GPS Space Segment/User Segment L5
Interfaces), June 2010.
[8] IS-GPS-800A (Navstar GPS Space Segment/User Segment L1C
Interface), June 2010.
[9] Wenhai Jiao, Qun Ding, Jianwen Li, et al. Monitoring and
Assessment of GNSS Open Services. The Jounal of Navigation
(2011), 64, S19-23, doi: 10.1017S0373463311000385.
[10]
Lu X C, Zhou H W. Methods of analysis for GNSS signal quality
(in Chinese). Sci Sin PhysMechAstron, 2010, 40(5): 528–533.
[11]
Anton, John, Hessin, Robert, Sapp, Joseph, Conley, Rob,
"Development of New GPS Performance Standards," Proceedings of
the 14th International Technical Meeting of the Satellite Division of
The Institute of Navigation (ION GPS 2001), Salt Lake City, UT,
September 2001, pp. 26-33.
[12]
Nagle, Tom, Renfro, Brent A., Lavrakas, John W., "Development
of a Performance Specification for Monitoring the GPS Civil
Service,"Proceedings of the 2005 National Technical Meeting of The
Institute of Navigation, San Diego, CA, January 2005, pp. 365-370.
[13]
http://www.navcen.uscg.gov/
[14]
http://www.glonass-center.ru/en/
[15]
http://www.beidou.gov.cn/
[16]
http://www.gps.gov/
[17]
http://www.esa.int/esaNA/galileo/
2
Appendix
Abbreviation List
GNSS
Global Navigation Satellite System
ICD
Interface Control Document
DOP
Dilution of Precision
GDOP
Geometry Dilution of Precision
PDOP
Position Dilution of Precision
TDOP
Time Dilution of Precision
HDOP
Horizon Dilution of Precision
VDOP
Vertical Dilution of Precision
SIS
Signal-In-Space
URE
User Ranging Error
URRE
User Range Rate Error
URAE
User Ranging Acceleration Error
TGD
Group Delay Time
ISB
Inter-System Bias
UTC
Coordinated Universal Time
UTCOE UTC Offset Error
PVT
Position, Velocity and Time
3