Russian system of differentional correction and monitoring
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About SDCM
Content

SDCM tasks
Integrity monitoring system solves the issue of operating quality estimation of space navigation system (SNS) GLONASS (RF) and GPS (USA).

The term "integrity monitoring" means the observation for system parameters and user informing about the cases of abnormal operation.

System carries out:
  • • on-line
  • • a posteriori

On-line monitoring
The goal of on-line monitoring (OM) is the quickest user warning concerning the initiation of operating failure SNS.

The tasks of on-line monitoring include:
•The estimation of pseudorange measurement errors based on GLONASS and GPS navigation space vehicle (NSV) in real time.
•  User informing concerning the values of these errors.

The errors of signals measurements of spase navigation system (SNS) included the following items:
• errors owing to ionospheric effect;
• errors owing to tropospheric effect
• ephemeris errors of NSV;
• the errors of clock-and-frequency corrections (CFC) of NSV.

On-line monitoring task:
the estimation of joint errors effect, added with ground and space segments of GLONASS and GPS systems, i.e. including the effect of ephemeris errors and clock-and-frequency corrections.

On-line functions:
• The estimation of pseudorange measurement errors based on GLONASS and GPS NSVin real time.
•  User informing concerning the values of these errors.
The estimation of pseudorange measurement errors are generated in discrete kind (index "In"), meaning the limited value of measurement error. Table 1 describes the correspondence of index to the value of limited error of pseudorange measurement ( e ) (metrical scale).

Table 1. The correspondence of index to value of limited error estimation of pseudorange measurement (e).

ln 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
e[] 2.4 3.4 4.85 6.85 9.65 12 15 20 30 50 100 200 500 1000 3000 >3000

The values e, corresponding to index in the range from 0 to 4 inclusive, coincide with the values of URA, transfered in navigation message GPS. So the user after taking the integrity message and GPS navigation message, could equally treat the estimations of pseudorange measurement errors.

The valuese,corresponding the index in the range from 5 to 15 inclusive, are chosen from considerations of convinience for the following analysis.


A posteriori monitoring
The goal of a posteriori monitoring (AM) is the estimation of different parameters, effected upon the quality of navigation definitions having used SNS.

The tasks of AM present the fixing process, when NSV operations anormal, and also the estimation of the following parameters:
•  vertical delay of navigation signals owing to ionospheric effect in the range of L1;
•  vertical delay of navigation signals owing to tropospheric effect;
•  errors of on-board ephemeris of GLONASS and GPS NSV;
•  errors of on-board clock-and-frequency corrections of GLONASS and GPS NSV
•  differences of GLONASS and GPS system time scales.
•  the number of observing GLONASS and GPSNSV;
•  determination of accuracy of horizontal and vertical coordinates components;
•  determination of accuracy of horizontal and vertical rate components;

Abnormal operation of NSV is the operation, when the total effect of ephemeris errors and errors of clock-and-frequency corrections exceeds the permissible limit.


SDCM structure
System of integrity monitoring of navigation fields ofNSV consists of the following components:

•  Monitoring points (MP).
•  The center of global monitoring (CGM).
•  Communication links betweenmonitoring points and the center of global monitoring.

Distribution of the results of on-line monitoring is performed by means of Internet technologies.


Monitoring points
The tasks of monitoring points present the collection of navigation data from NSV, pseudorange measurement of NSV and distribution in operational mode in the Center of global monitoring.

The main component of monitoring point is the station of measurement collection (SMC), which consist of GLONASS/GPS navigation receiver, which has the capacity to take the measurements on the basis of GLONASS and GPSNSV in L1 and L2 ranges in code phase and carrier phase.


The center of global monitoring

The center of global monitoring (CGM) is situated in Moscow. It consist of:

•  Sector of data collection
•  Sector of navigation and measurement data analysis
•  Sector of hardware/software support

The center of global monitoring has the heaviest duty in the frame of monitoring system, because the tasks of this center are the following:

•  data collection from the monitoring points
•  implementation of on-line monitoring function
•  implementation of a posteriori monitoring function
•  maintenance of database with monitoring results
•  user service


Communication links between monitoring points and the center of global monitoring
Communication links between Monitoring pointsandthe center of global monitoring are based on existing Internet channels and organised on the principle of VPN ( Virtual Private Network )

Recommendations on results application
Recommendations on results application.(recommendations.pdf)

Accepted abridgement

AM- a posteriori monitoring
SNS- space navigation systems
NSC- navigation space vehicle
OLM- on-line monitoring
MP- monitoring points
MS- monitoring station
CGM- center of global monitoring
CFC-clock-frequency corrections