Can you tell me something about GPS? What kinds are there on the market now?

Which is the global positioning system. Simply put, this is a satellite system consisting of 24 satellites covering the whole world. This system can ensure that four satellites can be observed at any point on the earth at any time, thus ensuring that satellites can collect the latitude, longitude and height of observation points, thus realizing the functions of navigation, positioning and timing. This technology can be used to guide planes, ships, vehicles and individuals to reach their destinations safely and accurately along selected routes.

Global Positioning System (GPS) is a new generation of space satellite navigation and positioning system jointly developed by the United States Army, Navy and Air Force in 1970s. Its main purpose is to provide real-time, all-weather and global navigation services for land, sea and air, and it is also used for some military purposes such as intelligence gathering, nuclear explosion monitoring and emergency communication. It is an important part of America's global dominant strategy. After more than 20 years of research and experiments, it cost 30 billion dollars. By1March 1994, 24 GPS satellite constellations with global coverage of 98% had been deployed.

The GPS global positioning system consists of three parts: the space part-GPS constellation; Ground control part-ground monitoring system; User equipment part -GPS signal receiver.

◆ The predecessor of ◆GPS

The predecessor of GPS system is the meridian satellite positioning system (Transit) developed by the US military, which was developed in 1958 and put into use in 64 years. The system works in a star network consisting of 5 to 6 satellites, which circles the earth 13 times a day at most, and can't give altitude information, so the positioning accuracy is not satisfactory. However, meridian system enables R&D department to gain the preliminary experience of satellite positioning, and verifies the feasibility of satellite positioning, which lays the foundation for the development of GPS system. Because satellite positioning shows great advantages in navigation, meridian system has great defects in submarine and ship navigation. The US Army, Navy, Air Force and civil departments urgently need a new satellite navigation system.

Therefore, the US Naval Research Laboratory (NRL) put forward a global positioning network plan called Tinmation, which consists of 12 to 18 satellites with an altitude of 10000km. An experimental satellite was launched in 1967, 1969 and 1974 respectively, and the atomic clock timing system was preliminarily tested on these satellites, which is the basis of accurate positioning of GPS system. The US Air Force, on the other hand, proposed a scheme of 62 1-b, and each constellation consisted of 4 to 5 satellites. Except for 1, all these satellites adopt inclined orbits with a period of 24 hours. This scheme spreads satellite ranging signals based on pseudo-random code (PRN), and its powerful function can also be detected when the signal density is lower than 1% of environmental noise. The successful application of pseudo-random code is an important basis for the success of GPS system. The navy's plan is mainly used to provide low-dynamic two-dimensional positioning for ships, while the air force's plan can provide high-dynamic services, but the system is too complicated. Because the development of two systems at the same time will cause huge expenses, and both plans here are aimed at providing global positioning, in 1973, the US Department of Defense merged the two systems into one, which is under the responsibility of the Joint Planning Bureau for Satellite Navigation and Positioning (JPO) led by the Department of Defense, and its office is located in the Air Force Space Office in Los Angeles. The agency has many members, including representatives from the US Army, Navy, Marine Corps, Ministry of Communications, National Defense Cartography Bureau, NATO and Australia.

compose

1。 Space part

The space part of GPS is composed of 24 working satellites, which are located 20±200km above the ground and evenly distributed on 6 orbital planes (4 in each orbital plane) with an orbital inclination of 55. In addition, there are four active backup satellites in orbit. The distribution of satellites makes it possible to observe more than four satellites anywhere in the world at any time, and maintain a geometric image with good positioning accuracy. This provides a global navigation capability that is continuous in time. GPS satellites generate two sets of codes, one of which is called C/ A code (Coase/Acquisition Code11023 MHz); One group is called P code (PROCISE code 10 123 MHz). Because of its high frequency, difficult interference and high positioning accuracy, it is controlled by the US military and has a password that ordinary people can't interpret, mainly serving the US military. C/ A code is mainly used by people after taking measures to deliberately reduce its accuracy.

2。 Ground control part

The ground control part consists of a main control station, five global monitoring stations and three ground control stations. The monitoring station is equipped with an accurate cesium atomic clock and receiver, which can continuously measure all visible satellites. Satellite observation data obtained by the monitoring station, including ionospheric and meteorological data, are transmitted to the main control station after preliminary processing. The main control station collects the tracking data of each monitoring station, calculates the orbit and clock parameters of the satellite, and then sends the results to three ground control stations. The ground control station injects these navigation data and the commands of the main control station into each satellite running overhead. This injection is once a day for each GPS satellite, and the last injection is made before the satellite leaves the injection station. If a ground station fails, the navigation information pre-stored by the satellite can still be used for a period of time, but the navigation accuracy will gradually decline.

3。 User equipment part

The user equipment part is a GPS signal receiver. Its main function is to capture the satellites to be tested selected according to a certain satellite cutoff angle and track the operation of these satellites. When the receiver captures the tracked satellite signal, it can measure the pseudo-range from the receiving antenna to the satellite and the change rate of the range, and demodulate the satellite orbit parameters and other data. According to these data, the microprocessor in the receiver can calculate the position according to the position calculation method, and calculate the latitude, longitude, altitude, speed, time and other information of the user's geographical position. 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. The receiver generally adopts two kinds of DC power supplies: internal and external. The purpose of setting internal power supply is not to interrupt continuous observation when replacing external power supply. When using off-board power supply, the battery will automatically charge. After shutdown, the battery in the machine supplies power to the RAM memory to prevent data loss. At present, various types of receivers are getting smaller and lighter, which is convenient for field observation.

global positioning system (GPS)

The basic principle of GPS navigation system is to measure the distance between the satellite with known position and the user receiver, and then the specific position of the receiver can be known by synthesizing the data of multiple satellites. In order to achieve this goal, the position of the satellite can be found out from the satellite ephemeris according to the time recorded by the on-board clock. The distance between the user and the satellite is obtained by recording the time when the satellite signal propagates to the user, and then multiplying it by the speed of light (due to the interference of the ionosphere in the atmosphere, this distance is not the real distance between the user and the satellite, but the pseudo-range (PR): when the GPS satellite works normally, it will constantly send navigation messages with pseudo-random codes (referred to as pseudo-random codes) consisting of binary symbols of 1 and 0. There are two kinds of pseudo codes used in GPS system, namely civil C/A code and military P(Y) code. The frequency of C/A code is 1.023MHz, the repetition period is one millisecond, and the code spacing is 1 microsecond, which is equivalent to 300 m; The frequency of P code is 10.23MHz, the repetition period is 266.4 days, and the code distance is 0. 1 microsecond, which is equivalent to 30m. Y code is formed on the basis of P code, which has better security performance. Navigation messages include satellite ephemeris, working conditions, 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. Each main frame of navigation information contains five subframes, each of which is 6s long. The first three frames 10 words; Repeat every 30 seconds and update every hour. The last two frames *** 15000b. The contents of navigation message mainly include telemetry code, conversion code, data block 1, 2, 3, and the most important one is ephemeris data. When the user receives the navigation message, he can know the distance between the satellite and the user by extracting the satellite time and comparing it with his own clock. Then, using the satellite ephemeris data in the navigation message, he can calculate the position of the satellite when sending the message and know the position and speed of the user in the WGS-84 geodetic coordinate system.

It can be seen that the function of the satellite part of the GPS navigation system is to continuously transmit navigation messages. However, because the clock used by the user receiver and the satellite clock cannot always be synchronized, in addition to the user's three-dimensional coordinates X, Y and Z, we should introduce a δ T, that is, the time difference between the satellite and the receiver, as an unknown number, and then use four equations to solve these four unknowns. So if you want to know where the receiver is, you must be able to receive signals from at least four satellites.

GPS prospect

GPS technology, with its all-weather, high-precision and automatic measurement characteristics, has been integrated into various application fields of national economic construction, national defense construction and social development as an advanced measurement method and new productivity.

With the end of the Cold War and the vigorous development of the global economy, the US government announced that from 2000 to 2006, under the premise of ensuring the national security of the United States is not threatened, the accuracy of GPS civil signals will be improved globally, and the single-point positioning accuracy using C/A code will be increased from 100 meters to 20 meters, which will further promote the application of GPS technology, improve productivity, operational efficiency, scientific level and people's quality of life, and stimulate. According to experts' prediction, in the United States, the market of car-mounted GPS navigation system alone will reach 3 billion dollars after 2000, and in China, the market of car-mounted navigation will also reach 5 billion yuan. It can be seen that the application prospect of GPS technology market is very considerable.

GPS characteristics

The main features of GPS are: (1) all-weather; (2) Global coverage; (3) The three-dimensional constant speed timing accuracy is high; (4) Fast, time-saving and efficient; (5) It has a wide range of uses and diverse functions.

GPS function

Main uses of GPS: (1) land applications, mainly including vehicle navigation, emergency response, atmospheric physical observation, geophysical resource exploration, engineering survey, deformation monitoring, crustal movement monitoring, municipal planning control, etc. (2) Marine applications, including the determination of the best navigation route of ocean-going ships, real-time ship dispatching and navigation, maritime rescue, marine treasure exploration, hydrogeological investigation, offshore platform positioning, sea level fluctuation monitoring, etc. (3) Aerospace applications, including aircraft navigation, remote sensing attitude control, orbit determination of low-orbit satellites, missile guidance, aviation rescue and manned spacecraft protection detection.

GPS application scope

It is mainly used for positioning and navigation of moving objects such as ships, cars and airplanes. For example:

1. Ocean navigation of ships and port diversion

2. Aircraft route guidance and approach landing

3. Automatic autonomous navigation

4. Ground vehicle tracking and urban intelligent traffic management

5. Emergency lifesaving

6. Personal Travel and Field Adventure

7. Personal communication terminal (integrated mobile phone, PDA and electronic map)

1. Time synchronization of power, post and telecommunications networks, etc.

2. Input of accurate time

3. Accurate frequency input

1. Geodetic survey and control survey of various grades.

2. Road and all kinds of line lofting

3. Underwater topographic survey

4. Crustal deformation measurement, deformation monitoring of dams and large buildings

5. Application of Geographic Information System

6. Control construction machinery (tire cranes, bulldozers, etc.). )

7. Precision agriculture

◆ Application of ◆GPS in Road Engineering

At present, the application of GPS in road engineering is mainly used to establish various road engineering control networks and determine the external control points of aerial survey. With the rapid development of high-grade highways, higher requirements are put forward for survey technology. Because of the long line and few knowledge points, it is not only difficult to lay out the network with conventional measurement methods, but also difficult to meet the requirements of high precision. At present, China has gradually adopted GPS technology to establish a first-class high-precision control network, and then used conventional methods to encrypt the wires. Practice has proved that the point error in the range of tens of kilometers is only about 2 cm, which has reached the accuracy that is difficult to achieve by conventional methods, and at the same time, the construction period has been greatly advanced. GPS technology is also applied to the control survey of the super-large bridge. Because there is no need for intervisibility, it can form a strong net shape, improve the point accuracy, and is also very effective for detecting the fulcrum of conventional measurement. GPS technology also has a broad application prospect in tunnel survey. GPS measurement does not need intervisibility, which reduces the intermediate links of conventional methods. Therefore, it is rapid and accurate, and has obvious economic and social benefits.

◆ Application of ◆GPS in automobile navigation and traffic management

Three-dimensional navigation is the primary function of GPS. Planes, ships, ground vehicles and pedestrians can use GPS navigator to navigate. Car navigation system is a new technology developed on the basis of Global Positioning System (GPS). The vehicle navigation system consists of GPS navigation, autonomous navigation, microprocessor, speed sensor, gyro sensor, optical drive and LCD. The combination of GPS navigation system with electronic map, wireless communication network and computer vehicle management information system can realize many functions such as vehicle tracking and traffic management.

(1) vehicle tracking

Using GPS and electronic map, the actual position of the vehicle can be displayed in real time, and can be enlarged, reduced, restored and changed at will. Can move with the target, so that the target always stays on the screen; But also can realize simultaneous tracking of multiple windows, multiple vehicles and multiple screens. This function can be used to track and transport important vehicles and goods.

(2) Providing tourist route planning and navigation.

Providing travel path planning is an important auxiliary function of car navigation system, including automatic path planning and manual path design. Automatic route planning means that the driver determines the starting point and the end point, and the computer software automatically designs the best driving route according to the requirements, including calculating the fastest route, the simplest route and the route that passes through the expressway section the least times. Manual route design means that the driver designs the starting point, the ending point and the passing point according to his own destination, and automatically establishes the route library. After the route planning is completed, the display can display the designed route on the electronic map, and at the same time display the driving path and method of the car.

(3) Information query

Provide users with a database of major landmarks, such as tourist attractions, hotels, hospitals, etc. , 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 area, and the vehicle information will be displayed on the electronic map of the control center in digital form.

(4) Traffic command

The command center can monitor the running state of vehicles in the area and reasonably dispatch the monitored vehicles. The command center can also talk to the tracked target at any time to implement management.

(5) Emergency assistance

Through the GPS positioning and monitoring management system, emergency assistance can be provided to vehicles in danger or accidents. The electronic map of the monitoring station displays help information and alarm targets, plans the optimal rescue plan, and reminds the personnel on duty to carry out emergency treatment with alarm sound and light.

◆ Other applications of ◆GPS

In addition to navigation, positioning and measurement, GPS can also release time and frequency information because of the accurate clock on the space satellite of GPS system. Therefore, based on the precise clock on the space satellite and under the monitoring of the ground monitoring station, transmitting accurate time and frequency is another important application of GPS, which can control accurate time or frequency and serve many engineering experiments. In addition, GPS can also be used to obtain meteorological data for some experiments and engineering applications.

Global Positioning System (GPS) is one of the most advanced high-tech technologies developed this year. Its advantages of global, omni-directional and all-weather navigation, positioning, timing and speed measurement will be more and more widely used in many fields. In developed countries, GPS technology has been applied to transportation and traffic engineering. At present, the application of GPS technology in road engineering and traffic management in China has just started. With the development of China's economy, the rapid construction of high-grade highways and the gradual deepening of GPS technology application research, its application in road engineering will be more extensive and in-depth, and play a greater role.

GPS type

There are many kinds of GPS satellite receivers, which are divided into geodesic type, all-station type, time service type, hand-held type and integrated type according to models. According to the purpose, it is divided into vehicle, ship, airborne, satellite and missile.

After more than 20 years of practice, it has been proved that GPS system is a high-precision, all-weather and global multifunctional radio navigation, positioning and timing system. GPS technology has developed into a multi-field, multi-mode, multi-purpose and multi-mode international high-tech industry.

◆ vehicle GPS

When the GPS positioning terminal is composed of hardware and software and used for vehicle positioning, it is called vehicle GPS, but it is not enough to just position, and it is called a third party to transmit these positioning information to the alarm center or vehicle GPS holder. Therefore, the GPS positioning system also includes GSM network communication (mobile phone communication), through which the satellite positioning information is sent to the third party by SMS. The short message is interpreted by microcomputer, and the vehicle position is displayed on the electronic map. In this way, the vehicle-mounted GPS positioning is realized. At the same time, the corresponding detection sensor is installed in the car, and the anti-theft alarm information can be sent to the third party by using the GSM network communication function of the car GPS positioning, or the alarm phone and short message can be directly sent to the car owner's mobile phone to complete the car GPS anti-theft alarm. It can be seen that the GSM network part of vehicle GPS positioning is actually a smart phone, which can communicate with third parties, and can also send information such as vehicle robbery, driver robbery and kidnapping to third parties. So vehicle GPS positioning is positioning, anti-theft and anti-robbery.

Automobile GPS navigation

1) system function

MP3 playback function:

Mp3 player can be used to play music, allowing users to adjust and relax during a boring journey. You can download your favorite music to your computer through the network first, and then transfer it to the directory named "Mp3" in the MMC/SD card of this machine through the card reader.

Touch screen handwriting input:

Handwritten input of English letters and Chinese characters and numbers is provided, which makes the inquiry more convenient.

Writing with a stylus in the center of the screen can display the text written by the user in the input box, list the input options given by the system in the selection box, and select the text to be input.

2) System configuration

Operating system: Microsoft Windows operating system. Net 4.2。

Electronic map: voice navigation system, inland navigation.

Microprocessor: Intel pxa255–300mhz

Built-in memory: 32MB flash memory +32MB SDRAM.

Display screen: 3.5 "semi-transparent TFT display panel, LED backlight module, resolution of 240x320 16 bits, 65K color display, supporting QVGA mode.

Satellite navigation: Built-in high-sensitivity GPS satellite positioning module.

Antenna: Built-in 25 x25 mm satellite receiving antenna.

Button/switch: power on/off; Volume control wheel; 5 shortcut keys (set, return, destination, zoom in and zoom out); 4 direction keys+1 execution key (up, down, left, right, execute); Hardware reset switch; System reset switch

Sound output: Support MP3 playback function.

Input and output: touch panel (touch panel); Input mode (stylus/handwriting recognition input); Internal expansion slot (SD/MMC); ; Speakers (a set of built-in speakers); Headphones (external 3.5mm mini jack); Data transmission line (USB 1. 1 synchronous transmission)

Rechargeable lithium battery: 1 100mAH rechargeable lithium battery; Start the GPS function, the screen can work continuously for 5 hours without backlight; Start the display of equal brightness on the GPS function screen for 3 hours; Standby time is as long as 19 days.

Power adapter: input 100-240VAC, output 5VDC,1a.

Working temperature: 0 ~ 55℃

Accessories: 256M MMC card, car antenna, car bracket, car sucker, car charger.

◆ Similar to car GPS

Similar to car GPS terminals, there are also positioning mobile phones and personal locators. Because GPS satellite positioning needs third-party positioning service, it needs to pay different monthly/annual service fees.

At present, all GPS positioning terminals have no navigation function. Because hardware and software need to be added, the cost is increased.

The car GPS advertisement we saw on TV is completely different from the car GPS above. It is a GPS navigation product. When navigation is needed, locate first, which is the starting point of navigation. This is different from real GPS positioning. It can't transmit the positioning information to the third party and the holder, because the navigator lacks the function of the mobile phone. For example, if you put the navigator in the car, your friend borrowed the car, and the navigator can't send you a message, then you can't find the location of the car. So the navigator can't locate it.

You said I bought a navigation phone, right? Think about it. You left your navigation phone in the car, and now the car has been stolen. Will that mobile phone call you or send a text message to a third party? It needs people to operate it. Therefore, the current navigation terminals have no positioning function.

The navigation terminal can navigate the route, so that you don't get lost in a strange place, draw the route to your destination, tell you the current location, surrounding facilities and so on.

At present, China has gained a huge market in the application of GPS. Many of them are navigation companies, but some of them are engaged in positioning management of GPS industry.

Various GPS/GIS/GSM/GPRS vehicle monitoring system software, the secondary development of GSM and GPRS mobile intelligent vehicle terminals, and the overall construction scheme of vehicle monitoring system. The system is widely used in public security, medical treatment, fire protection, transportation, logistics and other fields. This solution is based on NXP's PNX 1090 Nexperia mobile multimedia processor hardware and software, and is jointly developed by NXP and partner ALK Technology. NXP claims that this solution provides designers with everything they need to build a low-cost portable media player with navigation function and rich multimedia functions, including MP3 playback, standard and high-definition video playback and recording, FM radio, image storage and games. NXP uses its swGPS personal software running on PNX0 190 to realize GPS calculation, thus replacing a GPS baseband processor, thus reducing BOM cost and supporting field upgrade. /view/7773.htm