The principle of the main types of satellite navigation systems, development and characteristics Distinctions

Global Positioning System (Global Positioning System - GPS) is the United States from the 70s of this century began to develop, after 20 years, at a cost of 20 billion U.S. dollars, was fully completed in 1994, with the sea, land, and air for a full range of real-time three-dimensional navigation and positioning capabilities of a new generation of satellite navigation and positioning system. After nearly 10 years of China's surveying and mapping departments use shows that GPS to all-weather, high precision, automation, high efficiency and other notable features, to win the trust of the majority of survey and mapping workers, and successfully applied to geodesy, engineering surveys, aerial photogrammetry, means of delivery navigation and control, crustal movement monitoring, monitoring of engineering deformation, resource surveying, geodynamics and other disciplines, so as to the surveying and mapping field to bring a profound technological revolution. a profound technological revolution in the field of surveying and mapping.

With the continuous improvement of GPS, hard and software, the field of application is constantly expanding, and has been all over the national economy in various sectors, and began to gradually penetrate into people's daily lives.

GPS system features:

1, global, all-weather work:

can provide users with continuous, real-time three-dimensional position, three-dimensional speed and precision time. Not affected by weather.

2, high positioning accuracy:

Stand-alone positioning accuracy is better than 10 meters, using differential positioning, the accuracy can be up to centimeter and millimeter level.

3, multi-functional, wide range of applications:

With the deepening of people's understanding of GPS, GPS is not only in the measurement, navigation, speed, timing and other aspects of a wider range of applications, but also its application areas are constantly expanding.

This article is from 3s8.cn

GPS development

Before the emergence of the satellite positioning system, remote navigation and positioning is mainly used wireless navigation system.

1, radio navigation system

● Roland - C: working at 100KHZ, consisting of three ground navigation stations, navigation work area of 2000KM, the general accuracy of 200-300M.

● Omega (Omega): working in the teens of kHz. Consists of eight ground-based navigation stations with global coverage. Accuracy a few miles.

● Doppler system: using the principle of Doppler frequency shift, through the measurement of its frequency shift to get the parameters of the moving object (ground speed and yaw angle), to deduce the position of the vehicle, is a self-supporting waypoint deduction system. The error accumulates with the increase of range.

Disadvantages: the working area covered is small; the propagation of radio wave is affected by the atmosphere; the positioning accuracy is not high.

2, satellite positioning system

The earliest satellite positioning system is the U.S. Meridian Instrument System (Transit), which was developed in 1958 and formally put into use in 64. Due to the small number of satellites of this system (5-6 satellites), low operating altitude (average 1000KM), and long time interval from the ground station to observe the satellite (average 1.5h), it can not provide continuous real-time three-dimensional navigation, and the accuracy is low.

In order to meet the urgent requirements of the military and civil sectors for continuous real-time and three-dimensional navigation, the U.S. Department of Defense developed the GPS program in 1973.

3, GPS development

China's 3S professional station

GPS implementation plan *** in three stages:

The first stage for the program demonstration and preliminary design stage. From 1973 to 1979,*** four test satellites were launched. Ground receivers were developed and a ground tracking network was established.

The second stage is the comprehensive development and testing stage. From 1979 to 1984, 7 test satellites were launched, and receivers for various purposes were developed. Experiments showed that GPS positioning accuracy far exceeded the design standard.

The third stage for the practical network stage. 1989 February 4, the first GPS working satellite launched successfully, indicating that the GPS system into the engineering and construction stage. 1993 the end of the practical GPS network that is (21 + 3) GPS constellation has been completed, the future will be based on the plan to replace the failure of the satellite.

Principle of GPS

1. Composition of GPS system

GPS consists of three independent parts:

● Space part: 21 working satellites, 3 spare satellites.

● Ground support system: 1 main control station, 3 injection stations, 5 monitoring stations.

● User equipment part: receiving GPS satellite transmitting signals to obtain necessary navigation and positioning information, and completing navigation and positioning work through data processing.

GPS receiver hardware generally consists of host, antenna and power supply.

2, GPS positioning principle

The basic principle of GPS positioning is based on the instantaneous position of high-speed movement of satellites as a known starting data, the use of spatial distance backward rendezvous method, to determine the location of the point to be measured. As shown in the figure, assuming that t moment in the ground to be measured point on the placement of GPS receivers, can determine the GPS signal to reach the receiver time △ t, plus the receiver received by the satellite ephemeris and other data can be determined by the following four equations:

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The above four equations in the point to be measured in the coordinates of x, y, z and Vto for the unknown parameters. where di=c?ti (i=1, 2, 3, 4).

di (i=1, 2, 3, 4) is the distance between satellite 1, satellite 2, satellite 3, and satellite 4 to the receiver, respectively.

△ti (i=1, 2, 3, 4) is the time experienced by the signals from satellite 1, satellite 2, satellite 3, and satellite 4 to reach the receiver, respectively.

c is the propagation speed of the GPS signal (i.e., the speed of light).

The significance of each parameter in the four equations is as follows:

x, y, z are the spatial rectangular coordinates of the coordinates of the point to be measured.

xi, yi, zi (i=1, 2, 3, 4) are the spatial rectangular coordinates of satellite 1, satellite 2, satellite 3, satellite 4 at the moment of t,

which can be obtained from the satellite navigation message.

Vt i (i=1, 2, 3, 4) is the clock difference of the satellite clocks of Satellite 1, Satellite 2, Satellite 3, and Satellite 4, respectively, which is provided by the satellite ephemeris. www.3s8.cn

Vto is the clock difference of the receiver.

From the above four equations, the coordinates x, y, z of the point to be measured and the receiver's clock difference Vto can be solved.

DGPS Principle

The current GPS system provides better than 10 meters positioning accuracy, and in order to get a higher positioning accuracy, we usually use differential GPS technology: a GPS receiver is placed on the reference station for observation. According to the known precision coordinates of the reference station, the distance correction from the reference station to the satellite is calculated, and this data is sent out by the reference station in real time. User receivers in the GPS observation at the same time, but also received the reference station sent the correction number, and its positioning results are corrected, thereby improving positioning accuracy.

Differential GPS is divided into two main categories: pseudorange differential and carrier phase differential.

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1. Pseudo-distance differential principle

This is the most widely used type of differential. On the reference station, observe all the satellites, according to the known coordinates of the reference station and the coordinates of the satellites, find out the real distance of each satellite to the reference station at each moment. Then compared with the measured pseudo-distance, the pseudo-distance correction number, which will be transmitted to the user receiver to improve positioning accuracy.

This kind of differential, can get meter-level positioning accuracy, such as coastal widely used "beacon differential"

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2.carrier phase differential principle

Carrier phase differential technology, also known as RTK (Real Time), is a real-time positioning technology. Kinematic) technology, is a real-time processing of two stations carrier phase observation difference method. That is, the carrier phase collected by the reference station is sent to the user's receiver, the difference is solved coordinates.

Carrier phase difference can make the positioning accuracy of centimeter level. A large number of applications in the dynamic need for high-precision location of the field.