Projecte llegit
Títol: Characterization of the orbit error in the New C/NAV messages from modernized GPS satellites
Director/a: SANZ SUBIRANA, JAUME
Departament: MAT
Títol: Characterization of the orbit error in the New C/NAV messages from modernized GPS satellites
Data inici oferta: 16-03-2017 Data finalització oferta: 16-11-2017
Estudis d'assignació del projecte:
MU AEROSPACE S&T 15- MU MASTEAM 2015
| Tipus: Individual | |
| Lloc de realització: |
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| Paraules clau: | |
| GNSS, GPS, Navigation Message | |
| Descripció del contingut i pla d'activitats: | |
| The transmission of the Civil Navigation Message (CNAV) started
on 28 April 2014 for Block IIR-M and Block II-F Global Positioning System (GPS) satellites. CNAV provides a more flexible structure and better orbit representation compared to the legacy navigation message (LNAV). It is important to characterise the accuracy of the new messages and, for the first time, to perform precise point positioning based on the exclusive use of civil L1C/A and L2C observations. |
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| Overview (resum en anglès): | |
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The GPS modernization program involves a series of improvements, being the main objective the inclusion of new navigation signals to the satellites. The American Government has developed three new signals: L2C, L5 and L1C for civilian users. The traditional signal L1 C/A will continue to be transmitted in the future to preserve compatibility. The new L2C has two new codes: L2CM and L2CL, CM means Civil Moderate code and CL means Civil long code. These are modulated with an improved navigation message CNAV. On April 28th of 2014, the U.S. Air Force began to transmit the new CNAV message on L2C and L5 signals, through the new Block IIR(M) and IIF GPS satellites will be carrying these signals. The thesis is divided into two parts. The first part deals with the study of the new CNAV navigation message: its structure navigation message, as well as the new message types, the additional transmitted parameters to better represent the satellite orbital motion, and new equations to compute satellite coordinates. The differences (and similarities) with respect to contents of the Legacy Navigation (LNAV) messages have been highlighted. The first part of the thesis ends with the derivation of an important metric used to characterize the accuracy of the satellite orbits and clocks, known as Signal in Space Range Error (SISRE). The second part of the thesis consists of the development of algorithms for the satellite coordinates computation and its assessment with respect to reference orbits and clocks from the International GNSS Service (IGS). First, it has been developed a set of programs to download navigation files CNAV and LNAV from IGS-MGEX, files SP3 (precise GPS ephemerides and clocks) from IGS. Second the design and implementation of a devoted reader for the newest version of the navigation message RINEX 3.02 extended. Third, a set of algorithms were programmed to compute satellite coordinates with the new parameters and the new equations. Forth, a convertor module was needed to transform the obtained results to the SP3 format standard. The converted results were processed with the gLAB tool and obtain the SISRE value. The procedure outlined in this thesis allowed the computation of several statistics for both navigation messages, LNAV and CNAV. These statistics show that: in 2014, SISRE of CNAV was worse by a factor of two compared to the LNAV. This result is explained by the fact that the CNAV irregular update rate resulting in prediction times of up to four days while LNAV messages was updated once a day. In 2015, the statistics showed an improvement of the satellite coordinates. Computed with the CNAV message a further improvement of the CNAV performance is expected when full operational CNAV message capability will be achieved as part of the Generation Operational Control system (OCX) deployment. |
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