That is Global Positioning System (GPS). Simply put, it is a satellite system consisting of 24 satellites covering the entire globe. This system ensures that 4 satellites can be observed simultaneously at any point on the earth at any moment to ensure that the satellites can collect the latitude, longitude and altitude of that observation point in order to realize navigation, positioning, timing and other functions. This technology can be used to guide airplanes, ships, vehicles, and individuals, safely and accurately along selected routes to reach their destinations on time.
The Global Positioning System (GPS) is a new generation of space satellite navigation and positioning system jointly developed by the U.S. Army, Navy and Air Force in the 1970s. Its main purpose is to provide real-time, all-weather and global navigation services for the land, sea and air three major areas, and used for intelligence collection, nuclear explosion monitoring and emergency communications and some other military purposes, is the United States domination of the global strategy is an important component. After more than 20 years of research and experimentation, costing $ 30 billion, to March 1994, the global coverage rate of up to 98% of the 24 GPS satellite constellation has been completed.
The GPS global positioning system consists of three parts: the space part - the GPS constellation; ground control part - the ground monitoring system; the user equipment part---GPS signal receiver.
◆Predecessor of GPS
The predecessor of GPS system is a kind of meridian instrument satellite positioning system (Transit) developed by the U.S. Army, which was developed in 1958 and put into use in 64 years. The system worked with a network of five to six satellites, circled the Earth up to 13 times a day, and was unable to give altitude information and was not as accurate as it could have been in terms of positioning. However, the Meridian system allowed the R&D department to gain initial experience with satellite positioning and verified the feasibility of positioning by a satellite system, laying the groundwork for the development of the GPS system. As satellite positioning shows great superiority in navigation and the meridian instrument system exists for submarine and ship navigation of the great shortcomings. The United States Navy, Air Force and civilian sectors feel the urgent need for a new satellite navigation system.
To this end, the U.S. Naval Research Laboratory (NRL) proposed a 12 to 18 satellites called Tinmation composed of 10,000km altitude of the global positioning network plan, and 67 years, 69 years and 74 years each launched a test satellite, in these satellites on the preliminary test of the atomic clock timing system, which is the basis of the GPS system for precise positioning. And the U.S. Air Force proposed 621-B to each cluster of 4 to 5 satellites to form 3 to 4 clusters of plans, these satellites in addition to 1 using synchronous orbit the rest of the use of the period of 24h inclined orbit The plan to pseudo-random code (PRN) as the basis for the propagation of the satellite ranging signals, and its powerful features, when the signal density is lower than 1% of the ambient noise can also be detected. The successful use of pseudo-random codes is an important foundation for the success of the GPS system. The Navy's program was primarily used to provide low-dynamic 2D positioning for ships, while the Air Force's program was able to provide high dynamic service, however the system was too complex. Because of the enormous cost of developing both systems simultaneously and because both programs were designed to provide global positioning, in 1973 the U.S. Department of Defense (DoD) merged the two into a single program under the DoD-led Joint Program Office for Satellite Navigation and Positioning (JPO), with an office at the Air Force Space Division in Los Angeles. The agency has a large membership, including representatives from the U.S. Army, Navy, Marine Corps, Department of Transportation, Defense Mapping Agency, NATO, and Australia.
Composition
1. Space Segment
The space segment of GPS consists of 24 operational satellites located 20,200 kilometers above the earth's surface, evenly spaced on six orbital planes (four satellites per plane) with an orbital inclination of 55 degrees. In addition, there are four active backup satellites in orbit. The distribution of the satellites is such that more than four satellites can be observed anywhere on the globe, at any time, and geometrical images with good positional resolution can be maintained. GPS satellites produce two sets of codes, one set is called C / A code (Coarse / Acquisition Code11023MHz); a set of code called P code (Procise Code 10123MHz), P code because of the higher frequency, not easy to be interfered with, high positioning accuracy, and therefore subject to the U.S. military control, and have a code, general civilian control. And there is a password, general civilian can not be interpreted, mainly for the U.S. military services. C / A code artificial measures to deliberately reduce the precision, mainly open to civilian use.
2. Ground Control Section
The ground control section consists of a master control station, five global monitoring stations and three ground control stations. The stations are equipped with precision cesium clocks and receivers capable of continuously measuring all visible satellites. The stations transmit satellite observation data, including ionospheric and meteorological data, to the main control station after preliminary processing. The master control station collects tracking data from the monitoring stations, calculates the satellite orbit and clock parameters and sends the results to three ground control stations. The ground control station injects these navigation data and the command from the main control station into the satellite when each satellite is traveling overhead. This injection is performed once a day for each GPS satellite and a final injection is performed before the satellite leaves the injection station's range of operation. If a ground station failure, then the satellite in the pre-stored navigation information is still available for a period of time, but the navigation accuracy will be gradually reduced.
3. User equipment part
The user equipment part is the GPS signal receiver. Its main function is to be able to capture the satellite to be measured according to a certain satellite cutoff angle selected, and track the operation of these satellites. When the receiver captures the tracked satellite signals, it can measure the pseudo-distance from the receiving antenna to the satellite and the rate of change of the distance, and demodulate the satellite orbit parameters and other data. According to these data, the microprocessor computer in the receiver can carry out positioning calculation according to the positioning solution method and calculate the latitude, longitude, altitude, speed, time and other information of the user's geographical location. Receiver hardware and software and GPS data post-processing software package constitutes a complete GPS user equipment. the structure of the GPS receiver is divided into antenna unit and receiving unit two parts. Generally, the receiver adopts two kinds of DC power supply: internal and external. The purpose of setting the internal power supply is to replace the external power supply without interrupting the continuous observation. The internal battery is automatically charged when the external power supply is used. After shutdown, the internal battery supplies power to the RAM memory to prevent data loss. Currently, various types of receiver is becoming smaller and lighter, easier to use for field observation.
GPS principle
The basic principle of GPS navigation system is to measure the known position of the satellite to the distance between the user's receiver, and then a combination of multiple satellites data can be known to the receiver's specific location. To achieve this, the position of the satellite can be based on the time recorded by the on-board clock in the satellite ephemeris to find out. The distance from the user to the satellite is obtained by recording the time experienced by the satellite signal propagation to the user and multiplying it by the speed of light (due to the interference of the ionosphere of the atmosphere, this distance is not the real distance between the user and the satellite, but is a pseudo distance (PR): when GPS satellites are working normally, they will continually emit navigation messages with pseudo-random codes (abbreviated as pseudo-codes) consisting of 1 and 0 binary code elements. gps The pseudo-code used by GPS system has two kinds of pseudo-random codes, namely, civil C/A code and military P(Y) code. C/A code frequency is 1.023MHz, repetition period is one millisecond, and code spacing is 1 microsecond, which is equivalent to 300m; P code frequency is 10.23MHz, repetition period is 266.4 days, and code spacing is 0.1 microseconds, which is equivalent to 30m; while Y code is formed on the basis of P code, and the secrecy performance is better. The confidentiality performance is better. Navigation message includes satellite ephemeris, working condition, clock correction, ionospheric delay correction, atmospheric refraction correction and other information. It is demodulated from the satellite signal and transmitted on the carrier frequency with 50b/s modulation. The navigation message contains five subframes in each main frame each frame is 6 s. The first three frames each have 10 character codes; they are repeated every thirty seconds and updated every hour. The last two frames ***15000b. The contents of the navigation message are mainly telemetry code, conversion code, the 1st, 2nd and 3rd data blocks, of which the most important is the ephemeris data. When the user receives the navigation message, the satellite time is extracted and compared with their own clock to know the distance between the satellite and the user, and then use the satellite ephemeris data in the navigation message to deduce the location of the satellite transmitter message, the user's position in the WGS-84 geodetic coordinate system, such as speed and other information can be known.
It can be seen that the role of the satellite part of the GPS navigation system is to continuously transmit navigation messages. However, as the user receiver using the clock and satellite on-board clock can not always be synchronized, so in addition to the user's three-dimensional coordinates x, y, z, but also the introduction of a Δt, that is, the satellite and the receiver between the time difference as an unknown, and then with four equations will be the four unknowns solved. So if you want to know where the receiver is located, you need to be able to receive signals from at least 4 satellites.
GPS Prospect
Due to the all-weather, high-precision and automatic measurement characteristics of GPS technology, as an advanced means of measurement and a new productive force, it has been integrated into various application fields of national economic construction, national defense construction and social development.
With the end of the Cold War and the booming of the global economy, the U.S. government announced that during the period of 2000 to 2006, under the premise of ensuring that the U.S. national security is not threatened, the abolition of the SA policy, the accuracy of the GPS civil signals have been improved globally, and the accuracy of the single-point positioning using the C/A code has been improved from 100 meters to 20 meters, which will further promote the GPS technology This will further promote the application of GPS technology, improve productivity, operational efficiency, scientific level and people's quality of life, and stimulate the growth of GPS market. According to the prediction of relevant experts, in the United States, the market of GPS navigation system for automobiles alone will reach 3 billion dollars after 2000, while in China, the market of automobile navigation will also reach 5 billion RMB. It can be seen that the application of GPS technology market prospects are very considerable.
GPS features
The main features of the global positioning system: (1) all-weather; (2) global coverage; (3) three-dimensional fixed-speed timing high-precision; (4) fast time-saving and high efficiency: (5) the application of a wide range of multi-functional.
GPS function
The main uses of GPS: (1) land applications, including vehicle navigation, emergency response, atmospheric physical observation, geophysical resource exploration, engineering surveys, deformation monitoring, crustal movement monitoring, municipal planning and control, etc.; (2) oceanographic applications, including the determination of optimal voyage routes for ocean-going vessels, real-time scheduling of vessels and navigation, ocean rescue, ocean treasure hunting, hydrography and geophysics. (2) Marine applications, including determination of optimal range routes of ocean-going vessels, real-time scheduling and navigation of vessels, marine rescue, marine treasure hunting, hydrogeological measurements, positioning of marine platforms, and monitoring of sea level rise and fall, etc.; (3) Aerospace applications, including navigation of airplanes, remote sensing attitude control of airplanes, orbiting of low-orbit satellites, guiding of missiles, rescue of airplanes, and detection of protection of manned spacecrafts.
GPS application range
Mainly for ships, cars, airplanes and other moving objects for positioning and navigation. For example:
1. Ship ocean navigation and port diversion
2. Aircraft route guidance and approach landing
3. Automobile autonomous navigation
4. Ground vehicle tracking and urban intelligent traffic management
5. Emergency lifesaving
6. Personal travel and wilderness exploration
7. Personal communication terminals (with Personal communication terminal (integrated with cell phone, PDA, electronic map, etc.)
1. Time synchronization of electric power, postal and telecommunication networks
2. Accurate time input
3. Accurate frequency input
1. Geodetic and control surveys of various grades
2. Sampling of roads and various routes
3. Underwater topographic surveys
4.
4. Crustal deformation measurement, deformation monitoring of dams and large buildings
5. GIS application
6. Control of construction machinery (tire cranes, bulldozers, etc.)
7. Fine agriculture
◆ The application of GPS in road engineering
The application of GPS in road engineering is mainly used to establish the control network of various road projects and to determine the navigational system. various road project control networks and determination of aerial survey external control points. With the rapid development of high-grade highway, the survey technology puts forward higher requirements, due to the line is long, in order to know the point is less, therefore, with the conventional means of measurement is not only difficult to lay the network, and difficult to meet the requirements of high precision. At present, the country has gradually used GPS technology to establish the first level of high-precision control network of the line, and then encrypted with conventional methods of laying wire. Practice has proved that the point error within a few tens of kilometers is only about 2 centimeters, which achieves the precision that is difficult to achieve by conventional methods, and at the same time, it also greatly advances the construction period.GPS technology is also applied to the control measurement of mega bridges. As no pass-through is needed, it can form a stronger net shape and improve the point accuracy, and it is also very effective in detecting the pivot point of conventional measurement.GPS technology also has a wide range of application prospects in tunnel measurement.GPS measurement does not need pass-through, which reduces the intermediate links of the conventional method, and therefore, it is fast and accurate, and it has obvious economic and social benefits.
◆Application of GPS in Car Navigation and Traffic Management
Three-dimensional navigation is the primary function of GPS, and airplanes, ships, ground vehicles as well as pedestrians can navigate with GPS navigators. Car navigation system is a new technology developed on the basis of global positioning system GPS. The car navigation system consists of GPS navigation, auto-navigation, microprocessor, speed sensor, gyro sensor, CD-ROM drive, LCD display.GPS navigation system combined with electronic maps, radio communication network, computer vehicle management information system, can realize vehicle tracking and traffic management and many other functions.
(1) vehicle tracking
The use of GPS and electronic maps can be displayed in real time the actual location of the vehicle, and can be zoomed in, zoomed out, restore, change the map; can move with the target, so that the target is always kept on the screen; can also be realized multi-window, multi-vehicle, multi-screen tracking at the same time. Using this function, important vehicles and goods can be tracked for transportation.
(2) Provide travel route planning and navigation
Provide travel route planning is an important auxiliary function of the car navigation system, which includes automatic route planning and manual route design. Automatic route planning is determined by the driver to determine the starting point and destination, by the computer software according to the requirements of the automatic design of the best driving route, including the fastest route, the simplest route, through the highway section of the minimum number of routes calculated. Manual route design is designed by the driver according to their own destination design start point, end point and passing points, etc., automatically establish the route library. After the route planning is completed, the monitor is able to display the designed route on an electronic map and simultaneously display the vehicle running path and running method.
(3) Information Query
Provide users with the main objects, such as tourist attractions, hotels, hospitals and other databases, users can display their location on the electronic map. At the same time, the monitoring center can use the monitoring console to query the location of any target in the region, the vehicle information will be displayed in digital form on the electronic map of the control center.
(4) Call Command
The command center can monitor the vehicle operation status in the region and carry out reasonable scheduling for the monitored vehicles. The command center can also talk to the tracked target at any time to implement management.
(5) Emergency Assistance
The GPS positioning and monitoring management system can provide emergency assistance to vehicles in danger or in accidents. The electronic map of the monitoring station displays the help information and alarm target, plans the optimal assistance program, and reminds the duty personnel of emergency treatment with alarm sound and light.
◆Other Applications of GPS
Besides being used for navigation, positioning and measurement, GPS can release time and frequency information due to the precise clock carried on the space satellite of GPS system, therefore, based on the precise clock on the space satellite and under the supervision of the monitoring station on the ground, transmitting the precise time and frequency is another important application of GPS. precise time or frequency control, which can serve many engineering experiments. In addition, GPS can also be used to obtain meteorological data for certain experiments and engineering applications.
Global Positioning System GPS is one of the most pioneering high-tech developed this year, and its global, omnipotent, all-weather navigation and positioning, timing, speed measurement advantages are bound to be more and more widely used in many fields. In developed countries, GPS technology has begun to be applied to transportation and traffic engineering. At present, the application of GPS technology in China's road engineering and traffic management has just begun, with the development of China's economy, the rapid construction of high-grade highways and the gradual deepening of the study of the application of GPS technology, its application in road engineering will be more extensive and in-depth, and play a greater role.
GPS types
There are many types of GPS satellite receivers, according to the model is divided into geodesic, total station type, timing type, handheld, integrated; according to the use of the car-carried, ship-carried, airborne, star-carrying, bullet-carrying type.
After more than 20 years of practice has proved that the GPS system is a high-precision, all-weather and global radio navigation, positioning and timing multifunctional system. GPS technology has developed into an international high-tech industry with multiple fields, modes, applications and models.
◆Car GPS
When made through hardware and software GPS positioning terminal for vehicle positioning, known as the car GPS, but only the positioning is not enough, but also the positioning information to the alarm center or car GPS holders there, we call the third party. So the GPS positioning system also contains a GSM network communication (cell phone communication), through the GSM network by SMS to send satellite positioning information to the third party. Through the microcomputer to interpret the SMS message, in the electronic map to display the vehicle location. This realizes the vehicle GPS positioning. At the same time, in the car to install the appropriate detection sensors, the use of car GPS positioning of the GSM network communication function, the same can be sent to the third party anti-theft alarm information, or the alarm call, SMS directly to the owner's cell phone, complete the car GPS anti-theft alarm. It can be seen here that the GSM network part of the vehicle GPS positioning is actually a smart phone, which can communicate with the third party, and can also send the information about the vehicle being robbed, the driver being robbed, kidnapped, etc. to the third party. So the car GPS positioning is positioning, anti-theft, anti-robbery.
Car GPS Navigation
1) System Features
MP3 Playback Function:
Music playback is available with the mp3 player, which allows the user to regulate and relax during the monotonous and boring journey. You can download your favorite music to your computer through the Internet, and then transfer it to the MMC/SD card with the name "Mp3" directory through the card reader.
Touchscreen handwriting input:
Provides handwriting input of Chinese characters, English letters and numbers, which makes the query more convenient.
In the center of the screen with a pen and needle to write, you can display the user's words in the input box, in the selection box lists the input options given by the system, select the words to be input.
2) System Configuration
Operating System: Microsoft Windows CE .Net 4.2
E-Map: Voice navigation system, continent-wide navigation
Microprocessor: Intel PXA255 - 300MHz
Internal Memory: 32MB Flash ROM + 32MB SDRAM
Display: 3.5" Semi-Permeable TFT display panel, LED backlight module, 240x320 16-bit resolution, 65K color display, support QVGA mode
Satellite Navigation: Built-in high-sensitivity GPS satellite positioning module
Antenna: Built-in 25 x 25 mm satellite receiving antenna
Antenna: Built-in 25 x 25 mm satellite receiving antenna
Buttons/Switches: Power On/Off; Volume Control Wheel; 5 shortcut keys (Setup, Back, Destination, Zoom In, Zoom Out); 4 Direction Keys + 1 Execute Key (Up, Down, Left, Right, Execute); Hardware Reset Switch; System Reset Switch
Audio Output: Supports MP3 playback function
Rechargeable Li-Ion Battery: 1100mAH rechargeable Li-Ion Battery; Startup GPS function screen without backlight can continue to work for 5 hours; start the GPS function screen medium brightness display can continue to operate for 3 hours; standby time of up to 19 days
Power adapter: Input 100-240VAC Output 5VDC,1A
Working Temperature: 0 ~ 55 ℃
Accessories: 256M MMC card, car antenna, car
◆Similar to car GPS
Similar to car GPS terminals, there are positioning cell phones, personal locators, etc. GPS satellite positioning through a third-party positioning services, so you have to pay varying monthly/yearly service fees.
Currently all GPS positioning terminals, there is no navigation function. Because then need to add hardware and software, the cost increases.
The car GPS ads we see on TV, and the above car GPS are two completely different things. It is a GPS navigation products, when the need to navigate, the first positioning, that is, the starting point of navigation, which is different from the real GPS positioning, it can not send the positioning information to the third party and the holder, because of the lack of cell phone function in the navigator. For example, you put the navigator in the car, your friend borrowed the car and drove away, the navigator can't send the information to you, then you can't find the location of the vehicle. So the navigator is not able to locate.
You said I bought a navigation phone the line, think about it, you put the navigation phone in the car, and now the car is stolen, the phone will call you or a third party to send a text message? It needs a human to operate it. That's why the current navigation terminals don't have a locator function.
Navigation terminals can navigate routes so that you don't get lost in unfamiliar places, delineate routes so that you can reach your destination, and tell you your current location, and the surrounding facilities and so on.
China is now in the GPS should make a big market. Among them there are many companies are navigation. But there are also in the GPS industry to do location management.
A variety of GPS/GIS/GSM/GPRS vehicle monitoring system software, GSM and GPRS mobile intelligent vehicle-mounted terminals, the system's secondary development of vehicle monitoring system to build the overall program. The system is widely used in public security, medical, fire, transportation, logistics and other fields. The program is based on NXP's PNX1090 Nexperia mobile multimedia processor hardware and software jointly developed by NXP and partner ALK Technologies. NXP claims that the program provides designers with the ability to build a low-cost, multimedia-rich portable media player with the ability to navigate all the multimedia features required, these multimedia features include: MP3 playback, standard and high-definition video playback and recording, FM radio, image storage, and gaming. nXP implements GPS calculations with its swGPS Personal software running on the PNX0190, replacing a GPS baseband processor, which in turn reduces bill-of-materials (BOM) costs and supports field upgrades. /view/7773.htm