GPS tracker

The GPS tracker is a terminal with a built-in GPS module and a mobile communication module, and is used for transmitting the positioning data obtained by the GPS module to a server on the Internet through a mobile communication module (gsm/gprs network), thereby realizing on the computer. Query the terminal location.

The GPS receiver can receive time information accurate to the nanosecond level that can be used for timing; a forecast ephemeris used to predict the approximate location of the satellite in the next few months; and a broadcast ephemeris used to calculate the satellite coordinates required for positioning. The accuracy is from a few meters to tens of meters (different satellites, changing at any time); and GPS system information, such as satellite status.

The GPS receiver measures the distance from the satellite to the receiver. It is called pseudorange because it contains the error of the receiver satellite clock and the atmospheric propagation error. The pseudorange measured by the 0A code is called the UA code pseudorange, and the precision is about 20 meters. The pseudorange measured by the P code is called the P code pseudorange, and the precision is about 2 meters.

The GPS receiver decodes the received satellite signal or uses other techniques to remove the information modulated on the carrier and recover the carrier. Strictly speaking, the carrier phase should be referred to as the carrier beat frequency phase, which is the difference between the received satellite signal carrier phase affected by the Doppler shift and the phase of the receiver local oscillator generated signal. Generally, the epoch time determined by the receiver clock is measured, and the tracking of the satellite signal is kept, and the phase change value can be recorded, but the initial phase values of the receiver and the satellite oscillator at the start of observation are unknown. The phase integer of the epoch is also unknown, that is, the whole week ambiguity can only be solved as a parameter in data processing. The accuracy of the phase observation is as high as millimeter, but the premise is that the whole-circumference ambiguity is solved. Therefore, the phase observation value can be used only when the relative positioning and the continuous observation value are obtained, and the positioning accuracy is better than the meter level. Phase observations can be used.

How gps tracker works

How gps tracker works

According to the positioning method, GPS positioning is divided into single point positioning and relative positioning (differential positioning). Single point positioning is a way to determine the position of the receiver based on the observation data of a receiver. It can only be measured by pseudo-range observation and can be used for rough navigation and positioning of vehicles and ships. Relative positioning (differential positioning) is a method of determining the relative position between observation points based on observation data of two or more receivers. It can use either pseudo-range observation or phase observation. Geodesy or engineering measurement should be performed. Phase observations are used for relative positioning.

The GPS observations include errors such as the clock difference between the satellite and the receiver, the atmospheric propagation delay, and the multipath effect. They are also affected by the satellite broadcast ephemeris error during the positioning calculation. Most of the common errors are caused by relative positioning. Offset or weaken, so the positioning accuracy will be greatly improved. The dual-frequency receiver can offset the main part of the ionospheric error in the atmosphere according to the observation of two frequencies. When the accuracy is high and the distance between receivers is long (the atmosphere is obviously different) ), should use dual-frequency receiver.

In the positioning observation, if the receiver moves relative to the surface of the earth, it is called dynamic positioning, such as pseudo-single point positioning with accuracy of 30-100 meters for rough navigation and positioning of vehicles and ships, or for urban vehicle navigation and positioning. Pitch-precision differential positioning with meter-level accuracy, or centimeter-level phase differential positioning (RTK) for measuring stakeout, etc. Real-time differential positioning requires a data link to transmit observations from two or more stations in real time. In the positioning observation, if the receiver is stationary relative to the surface of the earth, it is called static positioning. When performing control network observation, it is generally observed by several receivers in this way. It can play GPS at the most limit. Positioning accuracy, a receiver dedicated to this purpose is called a terrestrial receiver and is the best performing class in the receiver. At present, GPS has been able to meet the accuracy requirements of crustal deformation observation, and IGS's perennial observing stations have been able to form a millimeter-scale global coordinate framework.

The GPS system consists of 24 satellites, and at any point on the earth, it can receive signals from at least 4 and up to 9 satellites.

For navigation positioning, the GPS satellite is a dynamic known point. The position of the star is calculated from the ephemeris transmitted by the satellite, a parameter describing the motion of the satellite and its orbit. The ephemeris broadcast by each GPS satellite is provided by the ground monitoring system. Whether the various equipment on the satellite is working properly and whether the satellite is always operating along a predetermined orbit is monitored and controlled by the ground equipment. Another important role of the ground monitoring system is to keep each satellite at the same time standard - GPS time system. This requires the ground station to monitor the time of each satellite and find the clock difference. It is then sent to the satellite by the ground injection station, which is then sent to the user equipment by the navigation message. The ground monitoring system of the GPS working satellite includes a master station, three injection stations and five monitoring stations.

The task of the GPS signal receiver is to capture the signals of the satellites to be tested selected according to a certain satellite height cut-off angle, and track the operation of these satellites, and transform, amplify and process the received GPS signals to measure The propagation time of the GPS signal from the satellite to the receiver antenna, the navigation message sent by the GPS satellite is interpreted, and the three-dimensional position, position, and even three-dimensional speed and time of the station are calculated in real time.

The navigation and positioning signal transmitted by the GPS satellite is an information resource that can be shared by countless users. For a wide range of users on land, sea and space, as long as the user has a receiving device capable of receiving, tracking, transforming and measuring GPS signals, ie a GPS signal receiver. GPS positioning signals can be used for navigation and positioning measurements at any time. Depending on the purpose of use, the GPS signal receivers required by the user also vary. At present, there are dozens of factories in the world that produce GPS receivers, and there are hundreds of products. These products can be classified according to principles, uses, functions,


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