Inside GNSS Media & Research

JUL-AUG 2018

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Page 50 of 59 J U L Y / A U G U S T 2 0 1 8 Inside GNSS 51 are based. e block GNSSBlockInterface defines a set of basic properties common to all objects that inherit its properties. Direct descendants of this GNSSBlockInterface are interfaces that describe the soware receiver, which range from a Channel interface to a PVT interface that serves as the top layer of the soware. Once the basic layers of the GNSS-SDR are defined, then the adapter blocks are used to implement the basic meth- ods of these interfaces and define some others if required (C. Fernández-Prades et alia, 2012). is in particular allows for an extremely flexible design in which adapter blocks could be swapped depending on the algorithm or signal to be processed. At the same time, each adapter block's dependencies connect GNSS-SDR with the GNU Radio API inheriting some func- tionality of the gr::block upon which the entire GNU Radio platform is defined. GLONASS FDMA Signal Model GLONASS satellites orbit Earth at a 64.8 degree inclination (GPS uses six planes at 55 degrees). is inclination is ideal to ensure good coverage of polar latitudes, where a significant por- tion of the Russian Federation territory is located. e satellites have an altitude of around 19,100 kilometers in a nearly circular orbit with eccentricity near 0 (again, see Additional Resources). e previous orbital parameters make the satellites have an orbital period of 11 hours, 15 minutes, and 28 seconds, with repeating ground tracks every 7 days, 23 hours, 27 minutes, and 28 seconds. As mentioned before, the GLONASS system uses FDMA for its C/A signal. e system now has allocated 14 frequency channels in the L1 band that are spaced from each other with a constant frequency offset. e received signal can be described as per Equation (1): where: PC is the power of signals with C/A code, C k is the C/A code sequence assigned to satellite number k, τ is the code phase received in ground, FIGURE 2 UML class diagram for objects added for GLONASS L1 C/A functionality

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