[Abstract]: This paper introduced the principle of GPS and its three major subsystems, focusing on the GPS system in the transportation application, including road works, car navigation and traffic management applications and other applications
I. Introduction Global Positioning System GPS
GPS global satellite positioning system in the early 70s the U.S. military, "meridian instrument satellite navigation and positioning," the sky with the technical development of global, all-around nature (land, marine, aviation and aerospace), all-weather advantage of the navigation and positioning, timing, Velocity Measurement. GPS sub-system by the three major components: space satellite systems, ground control system, the user receiving system.
Space Satellite System
Space satellite system consists of uniformly distributed in six orbital planes of 24 high-orbit satellites work, the orbital plane relative to the equatorial plane of inclination 55Ο, orbital plane spacing 60Ο. In each orbit plane, the angle from the poor satellite l 90Ο, any track on the west side of the adjacent satellites in orbit than the corresponding satellite ahead 30Ο. In fact, the number of satellites in space satellite systems to over 24, so that timely replacement of aging or damaged satellite, security system work properly. The satellite system can guarantee that any place on Earth available to users for more than four visible satellites.
Each satellite space systems every 12 hours (sidereal time) along the nearly circular orbit around the globe, the onboard high-precision atomic clock (fundamental frequency F = 10.23MHZ) control the radio transmitter in the "low-noise window" (radio window , the frequency range of 2 to 8 the minimum noise section of the antenna area of space telemetry and radio frequency interference measurement preferred) near the launch of L1, L2 two kinds of carrier, the receiving system to users around the world continuously transmit GPS navigation signals. GPS satellite network to protect the work of the world at any one time, any place can be on four or more satellites were observed (up to 11), to achieve continuous, real-time navigation and positioning.
GPS satellite navigation to the user to send messages is a non-zero binary data code D (t), rate fd = 50HZ. To save satellite power, enhanced GPS signal interference, confidentiality, to achieve remote satellite communications, GPS satellite by using the pseudo noise code for two of the D code modulation, namely, first D pseudo noise code modulated code (P code and C / A code), then the two noise code modulation in L1, L2 carrier on the two to form the user launches the GPS radio signal. Thus, GPS signals, including two carrier (L1, L2) and two pseudo-noise code (P code, C / A code). The frequency of the four GPS signals are derived from 10.23MHZ (the base-board atomic clock frequency) of the base frequency. Reference frequency signal with a certain ratio between the frequency. Where, P code for the exact code, the United States for their own interests, only the U.S. military, government agencies and approved by the U.S. government's civilian users, C / A code is rough code, its positioning and timing accuracy are lower than the P code At present, civilian customers around the world can be unrestricted free of charge.
Ground Control System
Ground monitoring system is composed of uniformly distributed in the U.S. and U.S. military bases on three oceans 5 stations, one master station and three into the substations. The system functions are: monitoring of space satellite systems, control, and to update each satellite's navigation message injection.
Ground control station system main tasks are:
Stations
With the GPS receiver measurements of each satellite pseudorange and range difference, collecting meteorological data, and data transfer to the main control point of observation. Five monitoring stations are no keep the value of the data collection center.
Master control station
Master Control Station to receive the station's GPS satellite data, satellite data, working status, the station into the station's own work and state data. According to the above types of data, complete the following tasks:
* Timely compilation of each satellite's navigation message and send it into the station.
* Control and coordination of monitoring stations, the injection of work between stations to test into the satellite navigation data is correct and whether the satellite navigation message is sent to the GPS user system.
* Diagnostic work satellites state, off track changes in the satellite position and attitude, adjust the spare satellite to replace failure of satellite.
Into the station
Accept the service of master control station and the satellite navigation data into the overflights of each satellites.
User reception system
User receiver system consists of radio sensor and computer technology to support the GPS satellite receiver and GPS data processing software component.
GPS receiver
GPS satellite receiver is the basic structure of the antenna unit and receiver unit in two parts. The main function of the antenna unit is: When the GPS satellite from rising on the horizon, can capture, tracking satellites, GPS receiver signal amplification. Receiving unit's primary role is: Record GPS signals and signal demodulation and filtering, to restore a GPS satellite navigation message sent, Solutions of the signal propagation time between stations and satellite carrier phase, real-time access to data or navigation by measuring the way post-processing to obtain positioning, velocity, timing and other data.
Microprocessor is the heart of GPS receiver, take the whole system of management, control and real-time data processing. Screen Monitor is a receiver with the machine operator to exchange components.
At present, the international has launched dozens of measuring GPS receivers, the manufacturers of the products towards the practical, lightweight, easy to operate, cheap and beautiful direction.
GPS data processing software
GPS data processing software is an important part of the GPS user system, its main function is the GPS receiver for satellite measurements recorded data, "Rough," "pre" and deal with the results of adjustment calculation, coordinate transformation and analysis integrated treatment. Solution was measured three-dimensional coordinates of points, measured body coordinates, velocity, direction and exact time.
GPS positioning technology is being developed high-tech, data-processing technology is being continually updated at each series of GPS receiver manufacturers have different characteristics developed processing software.
The basic method of GPS positioning
GPS positioning using passive measurement principles of space, that is placed in the measuring station GPS receiver system users, in every possible way to receive GPS satellite system to send various signals from the satellite computer station relations and solving the three-dimensional coordinate measuring stations.
Views on GPS signals from the different measurements, GPS positioning of the basic methods have the following forms:
* Pseudo-range measurement
* Carrier phase measurements
* Doppler measurements
* Satellite radio interferometry
For precise positioning, a GPS receiver is often not simply adopt a measurement, but mainly in some way, supplemented by other methods.
At present, the global positioning system has been widely used in military and civilian, and many other areas. GPS technology to be determined point by positioning the state is divided into static and dynamic positioning two categories. Static positioning is the location of the point to be determined in the process of constant observation, such as GPS applications in geodesy. Dynamic positioning is to be determined point in the moving vehicle, in observing the process of change, such as GPS in Marine Navigation. Static relative positioning accuracy of a few centimeters typically a few millimeters within the dynamic relative positioning accuracy typically a few centimeters to several meters range. On the GPS signal processing from the time is divided into real-time processing and post processing. Real-time processing is to receive satellite signals while one side is calculated to obtain the current position, velocity and time information; post-processing refers to the satellite signals recorded in some media, the back room unified data processing. In general, the static positioning users to use more post-processing, dynamic positioning customers to use real-time processing or post-processing.
Second, GPS Application in Transportation
1, GPS applications in road works
GPS in road engineering, the key is used to create various road works outside the control network and the determination of aerial control points. With the rapid development of highway, on investigation techniques put forward higher requirements, due to long lines, little known points, therefore, not only with conventional means of measurement traverse difficult and hard to meet the precision requirements. At present, the domestic use of GPS technology has been gradually established network of high-precision control circuit heads, such as Nanjing, Shanghai-Hangzhou Expressway, Shanghai section is to use GPS to establish the primary control network, and then use conventional methods of emplaced wire encryption. Practice shows that dozens of kilometers away in the position error is only 2cm or so difficult to achieve the accuracy of conventional methods, but also much earlier period. Zhejiang Bureau of Surveying and Mapping Using Wild 200 GPS Receiver features fast static positioning Surveying all of the preliminary test the line wire, fast, high-precision built hundreds of kilometers of expressway traffic control network, and achieved good results. GPS technology is also applied to the control of large bridge measurement. Because without links, as, may constitute a strong shape and improve the location precision, while the fulcrum of the testing routine is also very effective measure. If the construction of Jiangyin Yangtze River Bridge, the first conventional method of high precision network edges, and then use GPS to detect the nets, GPS monitoring network reached a millimeter accuracy, compared with conventional precision network in good agreement. GPS measurements in the tunnel has a wide application, GPS measurements do not pass, as the reduction of conventional methods of intermediate links, and therefore speed, high precision, with obvious economic and social benefits.
Differential GPS in Surveying and dynamic aspects of digital terrain model is mainly used in data acquisition, control point encryption, Centerline Layout, longitudinal measurements, and without external control points such as on-board GPS aerial. Tongji University in June 1994 tested in real-time phase difference KART satellite positioning system, achieved within 1km accuracy better than 2cm, so can be used to route control network encryption. GPS measurements include a three-dimensional information, can be used for digital terrain model data collection, Centerline Layout and longitudinal measurement. Setting out in the midline position, while access to longitudinal, in Centerline Layout need real-time data from the base station data link transmitted by the mobile station to provide real-time location of mobile stations, GPS devices do not like because, as can the direction of the theodolite therefore be combined with computer-aided design system, which can be seen on the computer screen coordinates of current location and design of the differences. Dynamic differential GPS used in airborne aerial survey in Germany and Canada have been successful, with carrier phase difference measured by three-dimensional coordinates of each of the camera center, but no longer need external control point measurement, and achieved good results.
2, GPS car navigation and traffic management applications
3D navigation is the primary function of GPS, aircraft, ships, ground vehicles and pedestrians can use GPS navigation receiver for navigation. Car navigation system GPS global positioning system developed on the basis of a new technology. GPS car navigation system consists of navigation, self-navigation, microprocessors, speed sensors, gyro sensors, CD-ROM drive, LCD display component.
GPS Navigation GPS receiver from the GPS satellite signal reception (3 above), find the latitude and longitude coordinates of the point, speed, time and other information. To enhance the vehicle navigation and positioning accuracy, differential GPS techniques commonly used. When the car driving to the underground tunnels, high rise buildings, highways and other obscure objects with less than a GPS satellite signal acquisition, the system can automatically import the self-navigation system, this time by the speed sensor detects the speed of motor vehicles moving through the micro-processing units data processing, velocity and time directly from the calculated distance ahead, gyro sensors detect directly forward, gyroscope can automatically store all data, even in the replacement tire temporary parking, the system can be reset.
From the GPS satellite navigation and self-navigate the vehicle position coordinates measured data, the way forward line with the actual driving track of certain errors, to correct these two errors, and the route map unification requires the use of map matching techniques , plus a map matching circuit, the line of car and electronic road map for real-time correlation matching error for automatic correction, then the map matching circuit is through micro-processing unit of the order process for quick handling, get the car in the electronic map the correct position to indicate the correct driving line. CD-ROM for storing road data and other information, LCD displays used to display navigation information.
GPS navigation system with electronic map, radio communication networks and computer integrated vehicle management information system, can achieve vehicle tracking and traffic management and many other features that include:
Vehicle Tracking
Using real time GPS and electronic maps showing the actual location of the vehicle, and any enlargement, reduction, reduction, exchange diagram; can move with the target, the target is always to keep the screen; can achieve multiple windows, multi-vehicle, multi-screen at the same time tracking. Using the function of important transport vehicles and cargo tracking.
Providing travel route planning and navigation
Providing travel route planning is an important car navigation system accessibility features, which include automatic route planning and design of artificial lines. Automatic route planning is determined by the driver starting point and destination, as required by the computer software automatically design the best driving route, including the fastest route, the easiest route, at least by the number of highway sections such as the calculation of the line. Artificial circuit design is the destination of the driver design based on their starting point, destination and waypoints, etc. to automatically set up line database. Route planning is completed, the display can display the electronic map design lines, and also shows the path and the method of running cars.
Information Query
Standard to provide users with the main object, such as tourist attractions, hotels, hospitals and other database users to the electronic map on the basis of the need for inquiry. Query information can be text, language and images displayed, and the electronic map display its location. Meanwhile, the monitoring center console can be used to monitor any target within the region where the query position, vehicle information center will be Shuzi form Kongzhi electronic map display.
(4) Call Command
Command center can monitor the status of vehicle operation within the region, has been monitoring vehicles on a reasonable schedule. Command center can also be tracked at any time with the goal of the call, practice management.
(5) Emergency assistance
Through GPS positioning and monitoring and management system can be dangerous in case of accident or emergency vehicles. Taiwan's electronic map display control information and alarm for assistance objectives, planning the optimal assistance programs, and to sound and light alarm to remind the emergency personnel on duty.
GPS technology in car navigation and traffic management research and application projects in China has just started now, and study abroad in this regard has already begun and has achieved some results. University of Calgary, Canada, a dynamic positioning system designed Le, the system includes a strapdown inertial system, two GPS receivers and a computer can be determined in the linear path has parameters for road management systems and services. Developed cities in the United States applied to road traffic management system, the system uses GPS and GIS to build a road database, the database contains a variety of existing data, such as the exact location of roads, road conditions, along the road facilities, the system was formal operation in 1995, the urban road traffic management play an important role. In recent years a variety of foreign-developed system for vehicle-induced, in which real-time vehicle location identified in the past mainly based inertial measurement systems, and wheel sensors, along with the development and the GPS showed the superiority of the two methods have replaced the former trend. GPS for urban vehicle positioning generally induced in the cities to set up a base station, GPS receiver base station launches real-time information, through the differential treatment can be calculated real-time location of the current location and the road to reach the target network optimization calculations, the electronic map will be shown the road out of reach in the most optimal route for the public security, fire fighting, emergency repairs, first aid and other transport services.
3, GPS and other applications
In addition to GPS for navigation, positioning, surveying, the GPS system as the space contained precise satellite clock time and frequency information can be released, therefore, to space satellites, the precise clock, based on the ground monitoring stations, the transmission precise time and frequency is another important application of GPS, the precise application of the function of time or frequency control, laboratory services for many projects. In addition, overseas information, weather data can be obtained using GPS, for some testing and engineering applications.
Global Positioning System GPS is the most recent development of groundbreaking high-tech, its global, all-round all-weather of navigation positioning, timing, speed advantage in many fields will definitely get more and more widely used . In developed countries, GPS technology has been applied to transportation and road works being. Currently, GPS technology in China road works and traffic management applications has just started, I believe that as China's economic development, the rapid construction of high-grade highways and the gradual application of GPS technology in depth, its application in road works will broader and deeper, and play a greater role.