How to improve the accuracy of GPS navigation and positioning

Definition

GPS positioning determines the user's three-dimensional coordinates by calculating the distance from the satellite to the receiver.

The errors in positioning and navigation come from the following aspects:

• Satellite-related errors include satellite clock errors, satellite hardware delay errors, satellite ephemeris errors, relativistic errors and satellite antenna offsets, etc. Including satellite clock error, satellite hardware delay error, satellite ephemeris error, relativistic error and satellite antenna offset, etc.
• Signal propagation related errors: including ionospheric delay error, tropospheric delay error, multipath effect error
• Receiver-related errors include receiver clock errors, receiver hardware delay errors, receiver antenna errors, and receiver noise errors.
• Other errors mainly include earth autotransmission error, earth solid tide error, ocean tide and atmospheric load error, etc.

It can be seen that there are many reasons for GPS errors. It is still very difficult to eliminate all these errors. However, we can reduce the impact of these errors as much as possible. Through observation, these errors are divided into systematic errors and accidental errors, such as relativistic effects. The errors are regular and systematic errors, which can basically be eliminated through formula calculation.

However, for the ionosphere, it is difficult to have a unified pattern due to its wide range and rapid weather changes.

Other types of satellite-related errors will not be discussed here. The following mainly introduces signal propagation-related errors and receiver-related errors.

Signal propagation related errors

1. Ionospheric error

The ionosphere refers to the area 60km-1000km above the ground. Affected by various rays in the sun, there are a large number of powered electrons and positive ions in the ionosphere, which has a great impact on the propagation of electromagnetic waves. Electromagnetic waves pass through the ionosphere. In the process, the propagation speed is affected by the electron density of the ionosphere and the frequency of the signal itself.

Since the ionosphere has different effects on electromagnetic waves of different frequencies, the ionospheric error can be well measured through a dual-frequency receiver.

2. The troposphere is the atmosphere layer with a height below 50km. In the atmosphere layer below 50km, the atmospheric refractive index depends on factors such as temperature, air pressure and relative humidity, and the signal propagation path will also be curved. Systematic biases in distance measurements due to the above reasons are known as tropospheric delays. Tropospheric delay is corrected through models and algorithms.

3. Multipath effect error

The multipath effect means that when the receiver is measuring somewhere, the receiver antenna can not only receive the signal from the satellite, but also receive the signal reflected from the ground surface or the walls of surrounding buildings. The reflected signal Reflection angle position, reflection direction may also be the position, and it is very difficult to eliminate multipath.

Mitigation measures

A, observation position

Due to the multipath effect caused by reflection, the observation location should avoid strong reflectors such as calm water, smooth walls, or hillsides, valleys, basins, etc. At the same time, the receiving antenna should not be too high to avoid increasing errors.

B. Installing a diameter suppression plate under the antenna can effectively reduce the signal reflected from the ground.

C. Extend the observation time. As the observation time lengthens, the multipath error will show periodic changes. We can smooth the impact of the error by increasing the observation time as much as possible. The normal time is more than 20 minutes. Of course, practical applications must be considered. Currently, people prefer rapid positioning. .

Other errors: Since we are making antennas, let’s talk about the antenna phase center error.

We guide satellite positioning and navigation by measuring the distance from the satellite to the receiver, that is, the distance from the phase center of the satellite transmitting antenna to the phase center of the receiver antenna. In fact, we often use the geometric center point of the receiver antenna as the actual observation point, which causes errors in the antenna geometric center and phase center. As for the antenna phase center error, the antenna manufacturer can provide the phase center error value through darkroom measurement.

Among the receiver-related errors, the clock error can be reduced through algorithms, and the receiver noise error antenna phase center can be reduced well by selecting an antenna with good signal-to-noise ratio and phase center and a high-quality feeder.

In conclusion, there are many factors that affect GPS positioning and navigation errors, many of which can be eliminated and weakened through models and algorithms. In terms of hardware, such as antennas, the errors can also be weakened or corrected by purchasing high-quality antennas.