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Application of crystal oscillator in Beidou navigation system

2024-08-30

Knowledge points in this period

overview of the beidou navigation system:

BDS (Beidou) is a global satellite navigation system developed by China.Space segment, ground segment and user segmentThree parts, currently in orbit satellite55 A. It can provide high-precision and high-reliability positioning, navigation and timing services for all kinds of users around the world, all-weather and all-time, and has the ability of short message communication, and has initially possessed the ability of regional navigation, positioning and timing. To serve global users, spatial signal accuracy will be better0.5m; global positioning accuracy will be better10meter, the speed measurement accuracy is better0.2m/s, timing accuracy is better 20nanoseconds; Asia-Pacific positioning accuracy will be better5meter, the speed measurement accuracy is better0.1m/s, timing accuracy is better10 nanoseconds, the overall performance is greatly improved.

Differences between Beidou and GPS

Beidou has more than one function that can send short messages, which is an exclusive secret.

Positioning accuracy is slightly worse than GPS in the horizontal direction, and slightly better than GPS in the height accuracy.

Timing accuracy is slightly worse than GPS

Advantages of Beidou satellite positioning system relative to GPS positioning system:

The Beidou system space segment uses a hybrid constellation composed of three orbiting satellites, which has strong anti-blocking ability, especially in low-latitude areas.

The Beidou system provides navigation signals with multiple frequency points, which can improve the service accuracy through the combination of multi-frequency signals.

Beidou system innovation combines navigation and communication capabilities, with real-time navigation, fast positioning, accurate timing, location reporting and short message communication services.

Beidou and GPS positioning system commonly used crystal oscillator:

Whether it is positioning navigation or short message service, TCXO with high stability is required as a ground receiver. At present, for professional handheld terminals with short message function, the TCXO frequencies used are mainly 10.000MHz and 16.320MHz, and TCXO with voltage control function can be selected according to the requirements of the scheme. For BDS GPS multimode

Positioning of the chip, to use 16.368MHz(16.367667,16.369) and 26MHz.

Special requirements of navigation system for crystal oscillator:

In satellite positioning and navigation applications, accurate time measurement is required when solving position and velocity information, includingSatellite clock and local clockTwo kinds of time information. Local clocks usually use crystal oscillators, which require less accuracy than satellite clocks, and clock drift can be eliminated as a common term for positioning and speed measurement errors.The quality of the clock signal output by the local crystal oscillator directly affects the performance of the receiver.The impact on the acquisition and tracking performance of satellite positioning and navigation signals is huge, especially in harsh working environments such as vibration and high dynamics.

In satellite navigation and positioning processing, the crystal oscillator of the satellite receiver is subject to various external interferences, and the output frequency and phase fluctuate.When the fluctuation is large, it will cause the receiver loop to lose lock, resulting in the loss of satellite signal.

The main errors of the satellite receiver tracking loop are:Thermal noise σtPLL, crystal noise and dynamic stress error θe, where the crystal noise is further divided into σ v caused by the phase noise of the crystal and θ A caused by the short-term stability.

The phase noise and short-term stability of the crystal oscillator are mainly determined by the frequency stability of the crystal oscillator, the Frequency Slope (the slope of frequency change under temperature change) and the G-Sensitivity (acceleration sensitivity). It can be seen from the above formula that the frequency stability, Frequency slope and G-Sensitivity of the crystal oscillator will have a greater impact on the performance of the PLL tracking loop of the satellite receiver, and are the main factors that cause the loss of lock of the GNSS receiver loop.

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Subsection

Therefore, these parameters need to be considered when selecting a crystal for a GNSS receiver.

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BDS navigation system commonly used crystal oscillator parameter requirements: