Unit 10

1. Read and translate the following text

The global navigation satellite system (glonass)

General information

The GLObal NAvigation Satellite System (GLONASS) is similar to GPS in that it is a space-based navigation system providing global, 24 hours a day, all weather access to precise position, velocity and time information to a properly equipped user. The system became fully operational in January 1996 and consists of 24 satellites in 3 orbital planes at 19,100 km altitude, corresponding to an 11 h 15 min orbital period. Orbital inclination is 648° as opposed to the 55° of GPS, this has a significant impact on operations at high latitudes. Each GLONASS satellite continuously broadcasts its own precise position as well as less precise position information for the entire constellation, but the transmitted data is in the form of Earth Centred Earth Fixed (ECEF) co-ordinates and extrapolation terms, as opposed to Keplerian parameters, as is the case for GPS. The user segment consists of the equipment necessary to track the GLONASS satellites and derive position, velocity and time from the satellite data and measurements. The GLONASS control segment is similar in purpose and function to its GPS counterpart. The Co-ordinational Scientific Informational Centre (CSIC) of the Russian Space Forces provides official information on GLONASS status and plans, information and scientific method services to increase the efficiency of GLONASS applications.

Each GLONASS satellite uses two carrier frequencies in the L band, which, contrary to the GPS implementation, are different for each satellite. The L1 band ranges from 1602-5625 MHz to 1615-5 MHz in jumps of 0-5625 MHz, while the L2 band ranges from 1246-4375 MHz to 1256-5 MHz in jumps of 0-4375 MHz. (Twenty four frequency channels are therefore generated for each of L1 and L2). Each of these signals is modulated by either or both of a 5-11 MHz precision (P) signal and/or a 0-511 MHz coarse/acquisition (C/A) signal. The binary signals are formed by a P code or a C/A code which is modulo 2 added to 50 bps data (on L1 only). The P and C/A signals are then modulo 2 added to L1 in phase quadrature (only P is present on L2). The P code is a pseudorandom sequence with a period of one second, while the C/A code is a pseudorandom sequence with a period of 1 msec. Contrary to GPS where all codes are unique to a specific satellite; a single GLONASS code is used for all satellites. GLONASS receivers duplicate the P and/or C/A codes and the transmission time is determined by measuring the offset that is to be applied to the locally generated code to synchronize it with the code received from the satellite.

In an effort to reduce the bandwidth utilized by GLONASS as well as to reduce interference in the radio astronomy band, the GLONASS operators have formulated a transitional frequency plan as follows: until 1998, frequency channels 13 through 21 will be avoided as much as possible by implementing an antipodal configuration, in which two satellites in the same plane and separated by 180 degrees broadcast on the same frequency. From 1998 to 2005, no channels above 13 will be used, with channel 13 used as little as possible. Beyond 2005, the band will be shifted from 0 to +12, to -7 to +6.