• Main elements of the satellite navigation system
    • Space segment
            Space segment composed of navigation satellites, which generate a group of radionavigational signals transferring a huge overhead information content simultaneously. Main functions of every satellite are- forming and beaming of radiosignals, which are necessary for users navigation determination and satellites onboard systems control.
    • Earth segment
            Earth segment is composed of cosmodrome, command-measuring complex (CMC) and control centre. Cosmodrome provides taking the satellites to the required orbits, during the first deploying of the navigation system, and also periodical compensation of the constellation on the scope of satellites fails. Command-measuring complex serves for the navigational satellites information supply, necessary for the navigation sessions implementation, and also for its control as the space crafts. Control Centre, connected with the cosmodrome and command-measuring complex, coordinates the operation of all the satellites systems.
    • Users segment
            User's segment is composed of users equipment. It serves for the navigation signals reception, navigation parameters measuring and measurements processing. For solving of the navigation problems, users equipment has special embedded computer. The variety of user's equipment provides the needs of ground, sea, aviation and space users.
  • Principle of Navigation system operation
           Modern satellite navigation is based on the use of no-request range measurements between navigational satellite and the user. It means that the information about the satellite's coordinates given to the user, is included into navigation signal. The way of range measurements is based on the calculation of the receiving signal time delay compared with the signals, generated by the users equipment.
  • Coordinate system
      Coordinate system (CS)- values, which are used to uniquely determine the position of the object.

      The "Parametry Zemli 1990" ("The Earth Parameters 1990") (PZ-90.11) reference document contains geometric and physical numerical geodetic parameters, characteristics of fundamental geodetic constants, reference ellipsoid, geocentric coordinate system and the Earth’s gravity field as well as information about their representation and implementation recommendations.

      The reference document was developed in Scientific-research center for survey and navigation support of the 27th Central research institute of Ministry of Defense of the Russian Federation.

      Translation by Information and Analysis Center for Positioning, Navigation and Timing (IAC PNT) Central Research Institute for Machine Building, Federal State Unitary Enterprise (FGUP TSNIIMASH).

      "PARAMETRY ZEMLI 1990" (PZ-90.11) Reference Document

  • Minimal quantity of the satellites, needed for users positioning
           In ideal case, when the measurements are precise and satellite time is identical with the user's equipment time the users positioning can be realized with 3 satellites.
      Actually satellites time differs from the time on the users equipment. So, for users positioning one more coordinate is necessary- time drift between users equipment and the satellite time. That's why four satellites are needed for the solving of navigation problem.
  • Almanach
           Almanach - is a package of ephemeris of all the satellites belong to global navigation system. Ephemeris - a coordinates package, which uniquely determine the satellites position and velocity.
  • Navigation satellites signals
          Every satellite has calibration oscillator of the reference frequency f0 = 10,23 МHz, which forms the signals from its oscillation, named L1 and L2. They are used as encoded signals transmissitters and data senders, they are also used for the most precise ranging between the user and the satellite.
  • Factors that affects degradation of accuracy
           Precision conditions of navigation satellite systems are formed by the main failures level and geometrical disposition of the used satellites and the user. Geometrical factor (or Dilution of Precision DOP) is a recalculation coefficient of the sporadic error of the radionavigation parameter into the error of the corresponding parameters determination.
      Position DOP (PDOP) – means accounting the components of the vector in space.
      Horizontal DOP (HDOP) - means accounting the components of the vector in the horizontal plane.
      Vertical DOP (VDOP)-means accounting the components of the vector in the vertical plane.
      Time DOP (TDOP)- means accounting the time.