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The cause of the positioning error of the car GPS locator.
- Aug 01, 2018 -

The causes of positioning errors of automotive GPS locators can be divided into three categories: satellite-related errors, errors related to signal propagation, and errors associated with automotive GPS locators. What are the errors related to the car GPS locator?

1. GPS GPS locator observation error

In addition to the resolution error of the observation, this type of error also includes the placement error of the GPS positioner antenna relative to the measurement station. According to experience, it is generally believed that the resolution error of the observation is about 1% of the signal wavelength. The observation error is an accidental error, and appropriately increasing the observation will significantly reduce its impact.

The placement error of the antenna of the Legal GPS Tracker Geofence Google Maps With RFID Camera Crash Sensor positioner relative to the center of the observation station mainly includes the error of the antenna leveling and centering error and the measurement of the antenna phase center height (antenna height). For example, when the antenna height is 1.6 m, if the antenna leveling error is 0.1°, the centering error of the optical plummet is thereby about 3 mm. Therefore, if it is in precision positioning work, it must be carefully operated to minimize the impact of such errors.

2. Car GPS Locator Clock

Automotive GPS locators are generally equipped with high-precision quartz clocks with a daily frequency stability of approximately 10-11. If the synchronization difference between the car GPS positioner clock and the satellite clock is 1 microsecond, the resulting equivalent distance error is about 300 m.

A more effective method for dealing with the clock difference of a car GPS locator is to introduce an unknown clock error parameter at each observatory, and solve it in the data processing together with the position parameter of the observing station. At this time, it is assumed that the clock difference is independent at each observation moment, and the processing is relatively simple. Therefore, this method is widely used in real-time dynamic absolute positioning. In the static absolute positioning, the GPS GPS locator clock difference can also be expressed as a polynomial form like a satellite clock, and the coefficients of the polynomial are solved in the adjustment calculation of the observation. However, this will involve the correctness of the assumptions made about the clock characteristics when constructing the clock difference model.

When the positioning accuracy is high, a high-precision external frequency standard (ie, time standard), such as a cesium atomic clock or a cesium atomic clock, can be used to improve the accuracy of the vehicle GPS positioner time standard. In the precision relative positioning, it is also possible to use the method of the difference of the observation values to effectively reduce the influence of the clock difference of the GPS locator of the automobile.

3. Car GPS locator antenna phase center deviation

In GNSS positioning, whether it is code pseudorange or phase pseudorange, the observations are based on the phase center position of the GPS locator antenna, and the phase center of the antenna should be theoretically consistent with its geometric center. However, in practice, the phase center position of the antenna varies with the intensity and direction of the signal input, that is, the instantaneous position of the phase center (generally referred to as the phase center) and the theoretical phase center position will be different. The influence of the deviation of the phase center of the antenna on the relative positioning result can be several millimeters to several centimeters depending on the performance of the antenna. Therefore, for precise relative positioning, this effect cannot be ignored. How to reduce the offset of the phase center is an urgent problem in antenna design.

In practice, if the same type of antenna is used and the same set of satellites are simultaneously observed on two or more observing stations not far apart, the influence of the phase center offset can be weakened by the difference of the observed values. However, at this time, the antennas of each observatory should be oriented according to the azimuth attached to the antenna so that it points to the magnetic north pole according to the compass. According to different accuracy requirements, the orientation deviation should be kept within 3 ° ~ 5 °.

4. Weekly jump and full-circumference ambiguity

The carrier phase observation accuracy is higher than the pseudorange observation, but there is a problem of the entire week ambiguity. In addition, the occlusion of the signal or the influence of external signals may cause a cycle slip during phase tracking, and a continuous long-term cycle jump may cause the signal to lose lock. Carrier phase observation is affected by the ambiguity and cycle slip of the whole week, which is a very critical issue in the data processing of precise positioning.

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