Composition and Principle of GPS Global Positioning System

The Global Positioning System (GPS) is a new generation of indoor space satellite navigation and positioning system jointly developed by the United States Army, Navy and Air Force in the 21st century. Its purpose is to provide real-time, all-day and global navigation services for the three major areas of land, sea and air, and to be used for some defense purposes such as intelligence collection, nuclear explosion monitoring and emergency communications. It is also an important part of the US global dominance strategy. component. After more than 20 years of scientific research and experiments and an investment of 30 billion US dollars, by March 1994, 24 GPS satellite constellations with a global coverage of 98% had been deployed.

The Global Positioning System consists of three parts

(1) The ground control part consists of the main control station (responsible for and coordinating the work of the entire road system), the ground antenna (with the cooperation of the main control station, transmits homing messages to the satellite), and the monitoring center (full data It consists of automatic collection core) and communication intelligent auxiliary system (transmitting data);

(2) Part of the indoor space consists of 24 satellites distributed in 6 planes;

(3) The customer equipment part is mainly composed of GPS receiver and satellite wireless antenna.

(Beitian tenth generation GPS module selection table)

Main features of GPS:

(1) All-day; (2) Global coverage; (3) Three-dimensional fixed speed and high precision on time; (4) Rapid, time-saving, labor-saving and efficient: (5) Wide range of uses.

Scope of application of Global Positioning System:

(1) Land applications, mainly including vehicle navigation, emergency response, atmospheric physics observation, geological engineering resource exploration, construction engineering measurement, deformation observation, plate movement detection, urban planning control and;

(2) Deep-sea applications, including sea-going ship navigation channel measurement, ship dynamic dispatch and navigation, deep-sea emergency rescue, deep-sea treasure hunting, geological structure measurement and deep-sea platform positioning, sea level adjustment detection, etc.; (

3) Aerospace engineering applications, including airport navigation, airline remote sensing attitude, low-orbit satellite orbit determination, cruise missile guidance technology, aviation rescue and manned spacecraft safety protection detection, etc.

There are many types of GPS satellite receivers, which are divided into geodetic, stationary, timing, handheld, and integrated types according to model specifications; according to their uses, they are divided into vehicle-mounted, ship-mounted, L-band, satellite-borne, and missile-borne. .

More than 20 years of practical experience has proven that the GPS system is a high-precision, all-day and global radio navigation, positioning and timing multi-purpose system. GPS technology has developed into a cross-domain, multi-channel, multi-functional and multi-model global national high-tech.

GPS basics

24 GPS satellites orbit the earth for 12 hours at an altitude of 12,000 kilometers above the earth, allowing more than 4 satellites to be observed at any time at any time on the ground.

(Beitian BeitianGPS moduleBE-280）

Because the satellite position is accurately known, in GPS observation, you can get the distance between the satellite and the receiver. Using the distance formula in the three-dimensional coordinates, using 3 satellites, you can form 3 expressions to solve the location of the observation point. (X,Y,Z). Fully consider the deviation between the satellite clock and the receiver clock. In fact, there are 4 unknown quantities, X, Y, Z and clock error. Therefore, a fourth satellite must be introduced and four expressions must be established to obtain the observations. Point geographic coordinates and elevation.

In fact, the receiver can often lock on more than 4 satellites. At this time, the receiver can be divided into several groups according to the distribution of the satellites, each group has 4 satellites, and then the group with the least deviation is screened out through the optimization algorithm as the accurate positioning, thereby improving performance.

Due to deviations in satellite orbits and satellite clocks, the power impact of the ionosphere and troposphere on signals, and artificial SA maintenance policies, the accuracy level of civilian GPS is only 100 meters. In order to improve the accuracy, differential signal GPS (DGPS) technology is widely used to establish a base station (differential signal station) to carry out GPS observations. The precise coordinates of the known base station are used to compare with the observation values ​​to obtain an adjustment number and publish it to the public. . After receiving the adjustment number, the receiver compares it with its own observation value to eliminate most of the deviations and obtain a more accurate location. Experiments have proven that using differential signal GPS, the accuracy level can be improved to 5 meters.