The technique or method of guiding the carrier from its starting point to its destination is called navigation.The navigation system measures and calculates the instantaneous motion state and position of the carrier, and provides it to the driver or autopilot to realize the correct operation or control of the carrier.With the development of science and technology, more and more navigation information sources are available, and more and more types of navigation systems are available.Take aviation navigation as an example, the airborne navigation systems available for equipment include inertial navigation system, GPS navigation system, Doppler navigation system, Roland C navigation system, etc. These navigation systems have their own features and advantages and disadvantages.Inertial navigation (hereinafter referred to as the inertial navigation), for example, the advantages of the system is: do not need any external information nor any outward radiation, can be in any medium and navigation of any environmental condition, and can output the aircraft's position, speed, position and posture, and other navigation parameters, system of wide frequency band, can track any motor vehicle movement, smooth navigation output data, short-term stability is good.However, the inertial navigation system has an inherent disadvantage: the navigation accuracy diverges with time, that is, the long-term stability is poor.GPS navigation systems have high accuracy. Even after the U.S. Department of Defense has added SA(SelectiveAvaila Bility) errors, the horizontal and vertical positioning accuracy of C/A code signals can reach 100 and 157m, respectively, and do not diverge over time. Such high accuracy and long-term stability are beyond the reach of ins.However, GPS navigation system also has its Achilles' heel: narrow frequency band. When the carrier makes high maneuvering movement, the code ring and carrier ring of the receiver are easy to lose the lock and lose the signal, thus losing the navigation ability completely.It relies entirely on navigation information from GPS satellites, is subject to others, and is subject to human interference and electronic deception.The remaining navigation systems have their own pros and cons.
All kinds of navigation system is hard to meet the navigation performance requirements when used alone, the effective way to improve the overall performance of navigation system is the integrated navigation technology, which USES two or more than similar navigation system for measuring and calculating the same navigation information to form a measurement, calculated from the measurement error and correction of the navigation system.The system that adopts integrated navigation technology is called integrated navigation system, and the navigation systems that participate in the combination are called subsystems
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