The basic architecture and characteristics of GPS

　　GPS is a kind of precise satellite navigation system. The system consists of 24 satellites orbiting the Earth that continuously send information about their position and time. These satellites are evenly distributed in six orbits with four satellites in each orbit. Ground-based GPS receivers can receive signals from 5 to 12 satellites. In order to realize the ground positioning function, the GPS receiver needs to receive at least four satellite signals, three of which are used to calculate the latitude, longitude and altitude of the GPS receiver, and the fourth signal provides synchronization time calibration.

　　GPS system is mainly divided into three parts: first, the satellite, in the sky to provide positioning information; Second, the control system maintains the normal operation of the satellite on the ground to ensure the health of the satellite; Third, the receiver, the part used by ordinary users. The principle of positioning is to divide the Earth into 12 transverse sections, each of which has two positioning satellites at an Angle of 180 degrees, so that standing at any point on the earth, there are always 12 positioning satellites overhead. The distance, coordinates and angles between satellites are known, and the distance between satellites and people can be measured. According to the geometric principle, the receiver can usually determine the two-dimensional coordinates, namely longitude and latitude, as long as it receives the information of three satellites, and the altitude can be determined after receiving the information of four satellites.

　　The current network of satellites (up to 27) operates in asynchronous, low-Earth orbit and covers the globe, keeping the positioning system operational. GPS receivers need to lock on at least four stars to provide location information. These long series of codes (or combinations of numbers) broadcast or transmitted by satellite are called pseudo-random codes. The GPS receiver can calculate the transmission time of the satellite through the known satellite pseudo-random code, the speed of light and the query table to maintain the satellite position, and then convert the transmission time to distance. Under the condition of multiple satellites (more than 4), the position of the GPS receiver can be calculated by solving the trigonometric equation, and the position of the user is also provided.

　　The GPS chip is composed of a radio frequency integrated circuit, a digital signal processing circuit and standard embedded GPS software. Radio frequency integrated circuit used in GPS rf signal detection and processing, digital signal processing circuit for processing intermediate frequency signal, the standard embedded GPS software used to search and track the GPS satellite signal, and according to these signals to solve the user coordinate and speed, its main market is in the equipment, automobile, wireless portable computational devices as well as some CPS professional users. FIG. 1 shows the block diagram of the handheld GPS system chip structure.

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