What is GPS?

Usually used for navigation, that is, as a satellite navigator.

Nokia's GPS wireless modules LD- 1W and LD-3W can be found on Nokia official website, which belong to Bluetooth GPS.

This is what you should see. 2500 yuan should include the package of genuine navigation software.

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The details are as follows:

1. Overview

Global Positioning System (GPS) is a new generation of satellite navigation and positioning system, which was developed by the United States in 1970s. It took 20 years and cost 20 billion dollars. 1994 is fully built, and it has all-round real-time three-dimensional navigation and positioning capabilities by land, sea and air. After nearly 10 years of application in China's surveying and mapping departments, it shows that GPS has won the trust of the majority of surveying and mapping workers with its remarkable characteristics of all-weather, high precision, automation and high efficiency, and has been successfully applied to geodesy, engineering survey, aerial photogrammetry, vehicle navigation and control, crustal movement monitoring, engineering deformation monitoring, resource investigation, geodynamics and other disciplines, bringing a profound technological revolution to the field of surveying and mapping.

With the continuous improvement of the software and hardware of GPS, the application fields have been continuously explored, which have spread all over the national economy and gradually penetrated into people's daily lives.

The GPS system includes three parts: the space part-GPS satellite constellation; Ground control part-ground monitoring system; User equipment part --GPS signal receiver.

2.satellites and constellations

A GPS satellite constellation is composed of 2 1 working satellites and 3 in-orbit standby satellites, and it is called (2 1+3)GPS constellation. These 24 satellites are evenly distributed on six orbital planes, with an orbital inclination of 55 degrees, and the orbital planes are separated by 60 degrees, that is, the orbital right ascension is separated by 60 degrees. The elevation distance between satellites in each orbital plane is 90 degrees, and the satellites in one orbital plane are 30 degrees ahead of the corresponding satellites in the adjacent orbital plane in the west.

At an altitude of 20,000 kilometers, for stars, when the earth rotates once, they will make a circle around the earth, that is, the time to make a circle around the earth is 12 sidereal time. In this way, for ground observers, they will see the same GPS satellite four minutes in advance every day. The number of satellites above the horizon varies with time and place. At least 4 satellites can be seen, and at most 1 1 satellite can be seen. When using GPS signals for navigation and positioning, in order to determine the three-dimensional coordinates of the site, four GPS satellites must be observed, which is called positioning constellation. The geometric position distribution of these four satellites in the observation process has certain influence on the positioning accuracy. At a certain time in a certain place, even the exact point coordinates can't be measured. This time period is called "gap period". But this time difference is very short, which does not affect the all-weather, high-precision, continuous and real-time navigation and positioning measurement in most parts of the world. The number of GPS working satellites is basically the same as that of test satellites.

3. Ground monitoring system

For navigation and positioning, GPS satellite is a dynamic known point. The position of the constant star is calculated according to the ephemeris transmitted by the satellite, which describes the motion and orbit parameters of the satellite. The ephemeris broadcast by each GPS satellite is provided by the ground monitoring system. Whether all kinds of equipment on the satellite work normally and whether the satellite has been running along the predetermined orbit should be monitored and controlled by the ground equipment. Another important function of the ground monitoring system is to keep all satellites in the same time standard-GPS time system. This requires the ground station to monitor the time of each satellite and find out the clock difference. Then it is sent to the satellite by the ground injection station, and the satellite sends it to the user equipment through the navigation message. The ground monitoring system of GPS working satellite includes a main control station, three injection stations and five monitoring stations.

4. User equipment

4. 1 GPS signal receiver

The task of the GPS signal receiver is to capture the signals of the satellites to be measured selected according to a certain satellite height cutoff angle, track the operation of these satellites, transform, amplify and process the received GPS signals, thus measuring the propagation time of the GPS signals from the satellites to the antenna of the receiver, interpreting the navigation messages sent by the GPS satellites, and calculating the three-dimensional orientation, position and even three-dimensional speed and time of the station in real time.

In static positioning, the GPS receiver is fixed in the process of capturing and tracking GPS satellites. The receiver measures the propagation time of GPS signal with high precision, and calculates the three-dimensional coordinates of the receiver antenna position by using the known on-orbit position of GPS satellite. Dynamic positioning is to measure the trajectory of a moving object with a GPS receiver. The moving objects where the GPS signal receiver is located are called carriers (such as sailboats, planes in the air, walking vehicles, etc.). The antenna of the GPS receiver on the carrier moves relative to the earth in the process of tracking the GPS satellite, and the receiver measures the state parameters (instantaneous three-dimensional position and three-dimensional speed) of the moving carrier in real time by using GPS signals.

The receiver hardware, internal software and GPS data post-processing software package constitute a complete GPS user equipment. The structure of GPS receiver is divided into two parts: antenna unit and receiving unit. For geodesic receivers, these two units are generally divided into two independent parts. During observation, the antenna unit is placed on the station, and the receiving unit is placed in an appropriate place near the station. The two units are connected into a complete machine through cables. Some also make the antenna unit and the receiving unit into a whole and put them on the test site during observation.

GPS receivers generally use batteries as power supply. At the same time, two kinds of DC power sources inside and outside the machine are used. The purpose of setting the internal battery is not to interrupt the continuous observation when replacing the external battery. In the process of using the external battery, the internal battery will automatically charge. After shutdown, the battery in the machine supplies power to the RAM memory to prevent data loss.

In recent years, many types of GPS geodetic receivers have been introduced in China. When various types of GPS geodetic receivers are used for precise relative positioning, the accuracy of dual-frequency receivers can reach 5mm+ 1PPM. The accuracy of single frequency receiver can reach 10mm+2PPM. Within a certain distance. The accuracy of differential positioning can reach sub-meter level to centimeter level.

At present, various types of GPS receivers are getting smaller and lighter, which is convenient for field observation. GPS and GLONASS compatible global navigation and positioning system receivers have come out.

4.2 Classification of GPS receivers

The navigation and positioning signal sent by GPS satellite is an information resource that can be shared by countless users. For the vast number of users on land, sea and space, as long as users have receiving equipment that can receive, track, convert and measure GPS signals, that is, GPS signal receivers. GPS signals can be used for navigation and positioning measurement at any time. According to different purposes, users need different GPS signal receivers. At present, there are dozens of factories producing GPS receivers in the world, and there are hundreds of products. These products can be classified according to their principles, uses and functions.

4.2. 1 Classification by the purpose of the recipient.

65438 0. Navigation receiver

This receiver is mainly used for navigation of mobile carriers, which can give the position and speed of the carriers in real time. This kind of receiver generally adopts C/A code pseudorange measurement, and the real-time positioning accuracy of single point is relatively low, generally 25mm, and 100mm when there is SA influence. This kind of receiver is cheap and widely used. According to different application fields, this kind of receiver can be further divided into:

Vehicle-mounted-used for vehicle navigation and positioning;

Nautical type-used for navigation and positioning of ships;

Aviation type-used for aircraft navigation and positioning. Because of the fast running speed of aircraft, it is required that aviation receivers adapt to high-speed movement.

Spaceborne-used for satellite navigation and positioning. Because the speed of the satellite is above 7km/s, the requirements for the receiver are higher.

2. Geodetic receiver

Geodetic receiver is mainly used for precision geodesy and precision engineering survey. This kind of instrument mainly uses the observation value of carrier phase for relative positioning, with high positioning accuracy. This instrument is complex in structure and expensive.

3. Timing receiver

This kind of receiver mainly uses the high-precision time standard provided by GPS satellites to serve time, and is often used for time synchronization in observatory and radio communication.

4.2.2 Classification by receiver carrier frequency

Single frequency receiver

Single-frequency receiver can only receive L 1 carrier signal, and determine the carrier phase observation value for positioning. Because ionospheric delay can not be effectively eliminated, single frequency receiver is only suitable for short baseline (

Dual frequency receiver

Dual-band receiver can receive L 1 and L2 carrier signals simultaneously. By using the difference of ionospheric delay between two frequencies, the influence of ionosphere on electromagnetic wave signal delay can be eliminated, so the dual-frequency receiver can be used for accurate positioning for thousands of kilometers.

4.2.3 Classification by number of receiver channels

A GPS receiver can receive signals from multiple GPS satellites simultaneously. In order to separate the received signals from different satellites and realize the tracking, processing and measurement of satellite signals, the equipment with this function is called antenna signal channel. According to the channel types owned by the receiver, it can be divided into:

Multichannel receiver

Sequential direct communication channel receiver

Multichannel receiver

4.2.4 Classification according to working principle of receiver

Code correlation receiver

The code correlation receiver uses code correlation technology to obtain pseudo-range observations.

Square receiver

The square wave receiver uses the square wave technology of the carrier signal to remove the modulation signal to recover the complete carrier signal. The phase difference between the carrier signal generated in the receiver and the received carrier signal is measured by a phase meter, and the pseudo-range observation value is determined.

Hybrid receiver

The instrument combines the advantages of the above two receivers, and can obtain both code phase pseudorange and carrier phase observation.

Interference receiver

This receiver uses GPS satellite as radio source and uses interferometry to measure the distance between two stations.