What is GPS?

That is, Global Positioning System. Simply put, this is a satellite system consisting of 24 satellites covering the world. This system can ensure that four satellites can be observed simultaneously at any point on the earth at any time, ensuring that the satellite can collect the longitude, latitude and altitude of the observation point in order to realize navigation, positioning, timing and other functions. This technology can be used to guide aircraft, 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 three major areas of land, sea and air, and is used for some military purposes such as intelligence collection, nuclear explosion monitoring and emergency communications. It is an important component of the US strategy of global dominance. After more than 20 years of research and experiments and a cost of US$30 billion, by March 1994, 24 GPS satellite constellations with a global coverage rate of 98% had been deployed.

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

◆The predecessor of GPS

The predecessor of the GPS system was a meridian satellite positioning system (Transit) developed by the US military. It was developed in 1958 and officially put into use in 1964. This system works with a star network composed of 5 to 6 satellites, orbiting the earth up to 13 times a day, and cannot provide altitude information, and its positioning accuracy is also unsatisfactory. However, the meridian system allowed the R&D department to gain preliminary experience in satellite positioning and verified the feasibility of positioning by satellite systems, paving the way for the development of the GPS system. Because satellite positioning shows great advantages in navigation and the meridian system has huge flaws in submarine and ship navigation. The U.S. Navy, Army, Air Force and civilian departments all feel the urgent need for a new satellite navigation system.

To this end, the U.S. Naval Research Laboratory (NRL) proposed a global positioning network plan of 12 to 18 satellites with an altitude of 10,000km called Tinmation, and launched it in 1967, 1969 and 1974. A test satellite was launched, and atomic clock timing systems were initially tested on these satellites, which is the basis for the precise positioning of the GPS system. The U.S. Air Force proposed the 621-B plan to form 3 to 4 constellations with 4 to 5 satellites per constellation. Except for one of these satellites, all of them use synchronous orbits and the rest use inclined orbits with a period of 24 hours. It is planned to propagate satellite ranging signals based on pseudo-random codes (PRN). Its powerful function can detect signal density when it is less than 1% of environmental noise. The successful application of pseudo-random codes is an important basis for the success of the GPS system. The Navy's plan is mainly used to provide low-dynamic 2D positioning for ships, while the Air Force's plan can provide high-dynamic services, but the system is too complex. Since developing two systems at the same time would cause huge costs and both plans here are designed to provide global positioning, in 1973 the U.S. Department of Defense merged the two into one, and established the Satellite Navigation and Positioning Joint Initiative led by the Department of Defense. Planning Office (JPO) leadership, and also established offices in the Air Force Space Agency in Los Angeles. The agency's membership includes representatives from the U.S. Army, Navy, Marine Corps, Department of Transportation, Defense Cartography Agency, NATO and Australia.

Constitution

1. Space part

The space part of GPS is composed of 24 working satellites. It is located 20200km above the earth's surface and is evenly distributed on 6 orbital planes (4 satellites per orbital plane). The orbital inclination angle is 55°. In addition, there are 4 active backup satellites operating in orbit.

The distribution of satellites allows more than 4 satellites to be observed anywhere in the world at any time, and maintains geometric images with good positioning accuracy. This provides a temporally continuous global navigation capability. GPS satellites generate two sets of codes, one is called C/A code (Coarse/Acquisition Code 11023MHz); the other is called P code (Procise Code 10123MHz). Because of its higher frequency, P code is not susceptible to interference and has high positioning accuracy. It is controlled by the US military and has a password that cannot be deciphered by ordinary people. It mainly serves the US military. After artificially taking measures to deliberately reduce the accuracy, the C/A code is mainly open to private use.

2. Ground control section

The ground control section consists of a main control station, 5 global monitoring stations and 3 ground control stations. Monitoring stations are equipped with sophisticated cesium clocks and receivers capable of continuously measuring all visible satellites. The satellite observation data obtained by the monitoring station, including ionospheric and meteorological data, will be transmitted to the main control station after preliminary processing. The main control station collects tracking data from each monitoring station, calculates the satellite's orbit and clock parameters, and then sends the results to three ground control stations. When each satellite moves overhead, the ground control station injects these navigation data and master control station instructions into the satellite. This injection occurs once per day for each GPS satellite, with a final injection before the satellite leaves the range of the injection station. If a ground station fails, the navigation information stored in the satellite will still be available for a period of time, but the navigation accuracy will gradually decrease.

3. User equipment part

The user equipment part is the GPS signal receiver. Its main function is to capture the satellites to be measured selected according to a certain satellite cut-off angle and track the movement of these satellites. After the receiver captures the tracked satellite signal, it can measure the pseudo-distance and distance change rate from the receiving antenna to the satellite, and demodulate satellite orbit parameters and other data. Based on these data, the microprocessor computer in the receiver can perform positioning calculation according to the positioning solution method, and calculate the longitude, latitude, altitude, speed, time and other information of the user's geographical location. The receiver hardware, on-board software and GPS data post-processing software package constitute a complete GPS user equipment. The structure of the GPS receiver is divided into two parts: the antenna unit and the receiving unit. Receivers generally use two types of DC power supplies, internal and external. The purpose of setting up the internal power supply is to not interrupt continuous observation when replacing the external power supply. The internal battery is automatically charged when using an external power source. After shutdown, the internal battery powers the RAM memory to prevent data loss. Currently, various types of receivers are getting smaller and lighter, making them easier to use for field observations.

GPS Principle

The basic principle of the GPS navigation system is to measure the distance between the satellite with a known position and the user receiver, and then combine the data of multiple satellites to know the reception The specific location of the machine. To achieve this, the satellite's position can be found in the satellite's ephemeris based on the time recorded by the onboard clock. The distance between the user and the satellite is obtained by recording the time it takes for the satellite signal to propagate 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 Pseudorange (PR): When the GPS satellite is operating normally, it will continuously transmit navigation messages using pseudo-random codes (referred to as pseudocodes) composed of 1 and 0 binary symbols. There are two types of pseudocodes used by the GPS system. , respectively, are the civilian C/A code and the military P(Y) code. The C/A code frequency is 1.023MHz, the repetition period is one millisecond, and the code spacing is 1 microsecond, which is equivalent to 300m; the P code frequency is 10.23MHz, and the repetition period is 266.4. The code spacing is 0.1 microsecond, which is equivalent to 30m. The Y code is formed on the basis of the P code and has better confidentiality. The navigation message includes satellite ephemeris, working conditions, clock correction, ionospheric delay correction, and atmosphere. 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 the navigation message contains 5 subframes, each frame is 6 seconds long. The first three frames have 10 characters each; they repeat every thirty seconds and are updated every hour. The last two frames are ***15000b. The contents of the navigation message mainly include telemetry codes, conversion codes, and data blocks 1, 2, and 3, the most important of which is ephemeris data. When the user receives the navigation message, he can extract the satellite time and compare it with his own clock to know the distance between the satellite and the user, and then use the satellite ephemeris data in the navigation message to calculate the position of the satellite when it transmitted the message. , the user’s position, speed and other information in the WGS-84 geodetic coordinate system can be known.

It can be seen that the function of the satellite part of the GPS navigation system is to continuously transmit navigation messages. However, since the clock used by the user's receiver and the satellite's onboard clock cannot always be synchronized, in addition to the user's three-dimensional coordinates x, y, and z, a Δt, which is the time difference between the satellite and the receiver, must be introduced as an unknown variable. Then use 4 equations to solve these 4 unknowns. So if you want to know the location of the receiver, you must be able to receive signals from at least 4 satellites.

GPS Prospects

Due to the all-weather, high-precision and automatic measurement characteristics of GPS technology, as an advanced measurement method and new productivity, it has been integrated into the national economic construction and national defense. Various application areas in construction and social development.

With the end of the Cold War and the booming global economy, the U.S. government announced that from 2000 to 2006, on the premise of ensuring that U.S. national security is not threatened, it will cancel the SA policy, and the accuracy of GPS civilian signals will be the highest in the world. The range has been improved, and the accuracy of single-point positioning using C/A codes has been increased from 100 meters to 20 meters. This will further promote the application of GPS technology, improve productivity, operating efficiency, scientific level and people's quality of life, and stimulate the GPS market growth. According to relevant expert predictions, in the United States, the market for car GPS navigation systems alone will reach 3 billion U.S. dollars after 2000, while in my country, the car navigation market will also reach 5 billion yuan. It can be seen that the application prospects of the GPS technology market are very promising.

GPS Features

The main features of the Global Positioning System: (1) All-weather; (2) Global coverage; (3) High-precision three-dimensional speed and timing; (4) Fast and time-saving High efficiency: (5) Widely used and multi-functional.

GPS functions

The main uses of the Global Positioning System: (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 optimal voyage route determination of ocean-going ships, real-time ship dispatching and navigation, marine rescue, marine treasure hunting, hydrogeological survey and offshore platform positioning, sea level rise and fall Monitoring, etc.; (3) Aerospace applications, including aircraft navigation, aerial remote sensing attitude control, low-orbit satellite orbit determination, missile guidance, aviation rescue and manned spacecraft protection and detection, etc.

GPS application scope

Mainly used for positioning and navigation of moving objects such as ships, cars, and airplanes.

For example:

1. Ship ocean navigation and port entry

2. Aircraft route guidance and approach and landing

3. Car autonomous navigation

4. Ground vehicle tracking and urban intelligent traffic management

5. Emergency rescue

6. Personal travel and wild adventure

7. Personal communication terminal (Integrated with mobile phones, PDAs, electronic maps, etc.)

1. Time synchronization of electricity, postal and telecommunications, communications and other networks

2. Grant of accurate time

3. Acquisition of accurate frequencies

1. Various levels of geodetic survey and control survey

2. Staking out roads and various lines

3 .Underwater terrain measurement

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

5. GIS application

6. Engineering machinery (tires Crane, bulldozer, etc.) control

7. Precision agriculture

◆Application of GPS in road engineering

The application of GPS in road engineering is currently mainly Used to establish various road engineering control networks and determine aerial survey external control points, etc. With the rapid development of high-grade highways, higher requirements have been placed on survey technology. Due to long lines and few knowledge points, it is not only difficult to lay out the network using conventional measurement methods, but also difficult to meet high-precision requirements. At present, China has gradually adopted GPS technology to establish a high-precision control network at the first level of the line, and then used conventional methods to lay out conductor encryption. Practice has proven that the point error within a range of tens of kilometers is only about 2 centimeters, achieving an accuracy that is difficult to achieve with conventional methods and also greatly advancing the construction schedule. GPS technology is also used in the control measurement of very large bridges. Since there is no need for a clear view, a strong network shape can be formed to improve point accuracy. It is also very effective in detecting the fulcrum of conventional measurements. GPS technology also has broad application prospects in tunnel measurement. GPS measurement does not require visibility and reduces the intermediate links of conventional methods. Therefore, it is fast, highly accurate, and has obvious economic and social benefits.

◆Application of GPS in car navigation and traffic management

Three-dimensional navigation is the primary function of GPS. Aircrafts, ships, ground vehicles and pedestrians can all use GPS navigators for navigation. . The car navigation system is a new technology developed based on the global positioning system (GPS). The car navigation system consists of GPS navigation, autonomous navigation, microprocessor, vehicle speed sensor, gyro sensor, CD-ROM drive, and LCD display. The GPS navigation system is combined with electronic maps, radio communication networks, and computer vehicle management information systems to achieve many functions such as vehicle tracking and traffic management.

(1) Vehicle tracking

Using GPS and electronic maps, the actual location of the vehicle can be displayed in real time, and the vehicle can be enlarged, reduced, restored, and changed at will; it can move with the target, Keep the target on the screen all the time; you can also achieve simultaneous tracking of multiple windows, multiple vehicles, and multiple screens. This function can be used to track and transport important vehicles and cargo.

(2) Providing travel route planning and navigation

Providing 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 where the driver determines the starting point and destination, and the computer software automatically designs the best driving route according to the requirements, including the calculation of the fastest route, the simplest route, and the route with the least number of highway sections. Manual route design is where the driver designs the starting point, end point, and passing points according to his or her destination, and automatically establishes a 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 car's operating path and operating method.

(3) Information query

Provide users with a database of major objects, such as tourist attractions, hotels, hospitals, etc., and users can display their locations 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 in digital form on the electronic map of the control center.

(4) Traffic command

The command center can monitor the operating status of vehicles in the area and conduct reasonable dispatching of monitored vehicles. The command center can also communicate with the tracked target at any time and 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 assistance plan, and uses alarm sounds and lights to remind the personnel on duty to carry out emergency response.

◆Other applications of GPS

In addition to being used for navigation, positioning, and measurement, GPS system’s space satellites carry precise clocks that can publish time and frequency information. Therefore, Based on the precise clock on the space satellite and under the supervision of the ground monitoring station, transmitting precise time and frequency is another important application of GPS. This function can be used for precise time or frequency control and can serve many engineering experiments. In addition, GPS can also be used to obtain meteorological data for certain experimental and engineering applications.

The Global Satellite Positioning System (GPS) is one of the most groundbreaking high-tech technologies developed this year. Its global, omnipotent, and all-weather navigation, positioning, timing, and speed measurement advantages are bound to be used in many applications. are increasingly widely used in the field. In developed countries, GPS technology has begun to be used in transportation and traffic engineering. At present, the application of GPS technology in China's road engineering and traffic management has just started. With the development of China's economy, the rapid construction of high-grade highways and the gradual deepening of research on the application of GPS technology, its application in road engineering will also Broader and deeper, and with greater impact.

GPS types

There are many types of GPS satellite receivers, which are divided into geodetic, total station, timing, handheld, and integrated types according to their models; they are divided into vehicle-mounted types according to their uses. , ship-borne, airborne, space-borne, missile-borne.

After more than 20 years of practice, the GPS system has been proven to be a high-precision, all-weather and global multi-functional system for radio navigation, positioning and timing. GPS technology has developed into an international high-tech industry with multiple fields, multiple modes, multiple uses, and multiple models.

◆Vehicle GPS

When a GPS positioning terminal is used for vehicle positioning through hardware and software, it is called vehicle-mounted GPS. However, positioning alone is not enough, and this The positioning information is transmitted to the alarm center or the vehicle GPS holder, which we call a third party. Therefore, the GPS positioning system also includes GSM network communication (mobile phone communication), and satellite positioning information is sent to a third party through the GSM network by SMS. The microcomputer interprets the text messages and displays the vehicle location on the electronic map. In this way, vehicle GPS positioning is achieved. At the same time, by installing corresponding detection sensors on the car and using the GSM network communication function of the car's GPS positioning, the anti-theft alarm information can also be sent to a third party, or the alarm phone number or text message can be sent directly to the car owner's mobile phone to complete the vehicle installation. GPS anti-theft alarm. It can be seen here that the GSM network part of the vehicle GPS positioning is actually a smartphone, which can communicate with a third party and can also send information such as the vehicle was robbed, the driver was hijacked, or was kidnapped to the third party. Therefore, vehicle GPS positioning is used for positioning, anti-theft and anti-robbery.

Car GPS Navigation

1) System Features

MP3 playback function:

Use the mp3 player to play music, allowing users to Get some comfort and relaxation during the monotonous journey. You can first download your favorite music to the computer through the Internet, and then transfer it to the MMC/SD card of the machine through the card reader to the directory named "Mp3".

Touch screen handwriting input:

Provides handwriting input of Chinese characters, English letters and numbers, making inquiries more convenient.

Use the stylus to write in the center of the screen, and the words written by the user will be displayed in the input box. The input options given by the system will be listed in the selection box, and you can select the words you want to input.

2) System configuration

Operating system: Microsoft Windows CE .Net 4.2

Electronic map: Voice navigation system, continent-wide navigation

Microprocessor: Intel PXA255 – 300MHz

Built-in memory: 32MB Flash ROM 32MB SDRAM

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

Satellite navigation: built-in high-sensitivity GPS satellite positioning module

Antenna: built-in 25 x25 mm satellite receiving antenna

Buttons/switches: Power on/off; volume control wheel; 5 shortcut operation keys (settings, return, destination, zoom in, zoom out); 4 direction keys and 1 execution key (up, down, Left, right, execute); hardware reset switch; system reset switch

Sound output: supports MP3 playback function

Input and output: touch panel (touch control 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 cable (USB1.1 synchronous transmission)

Rechargeable lithium battery: 1100mAH rechargeable lithium battery; when the GPS function is turned on, the screen can work continuously for 5 hours without backlight; when the GPS function is turned on, the screen will work continuously for 3 hours with medium brightness display; the standby time is up to 19 days

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

Working temperature: 0～55℃

Accessories: 256M MMC card, vehicle antenna, vehicle bracket, vehicle Suction cup, car charger

◆Similar to car GPS

Similar to car GPS terminals are positioning mobile phones, personal locators, etc. GPS satellite positioning requires third-party positioning services. There are varying monthly/annual service fees.

Currently, all GPS positioning terminals do not have navigation functions, which increases the cost. The car GPS advertisements seen on TV are completely different from the above-mentioned car GPS. It is a GPS navigation product. When navigation is needed, the first positioning is the starting point of navigation. This is different from the real GPS positioning. It cannot transmit positioning information to third parties and holders because the navigator lacks the mobile phone function. For example, if you put the navigator in the car and your friend borrows the car and drives away, the navigator cannot send information to you. Then you cannot find the vehicle location. So the navigator cannot locate.

You said I bought a navigation phone, right? 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. Send text messages? It requires people to operate it.

Therefore, current navigation terminals do not have positioning functions.

The navigation terminal can navigate routes so that you don’t get lost in unfamiliar places, draw a route for you to reach your destination, tell you your current location, surrounding facilities, etc.

China currently has a large market in GPS. There are many companies in the navigation industry, but there are also companies doing positioning management in the GPS industry.

Various GPS/GIS/GSM/GPRS vehicle monitoring system software, GSM and GPRS mobile intelligent vehicle terminals, and overall system construction solutions for secondary development of vehicle monitoring systems. The system is widely used in public security, medical, and firefighting , transportation, logistics and other fields. The solution 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 solution provides everything designers need to build a low-cost, multimedia feature-rich portable media player with navigation capabilities. These multimedia features include: MP3 playback, standard and high-definition video playback and recording, FM Radio, image storage and games. NXP implements GPS calculations with its swGPS Personal software running on the PNX0190, replacing a GPS baseband processor, reducing bill of materials (BOM) costs and enabling field upgrades.