1 car navigation principle 1. 1 Positioning and Navigation The positioning of GPS is to use the principle of basic triangulation of satellites. The GPS receiver measures the distance by measuring the transmission time of radio signals, and uses the distance to determine the position of the satellite in space. The GPS module receives the positioning signal of the satellite and calculates its own position. (Longitude, latitude, altitude), time and movement status (speed, heading) are sent to the SCM once per second and stored so as to provide positioning information at any time. This is an observation method with high orbit and precise positioning. The GPS satellite system, on-board unit, GSM network, and vehicle tracking and monitoring center form part of the GPS vehicle navigation system. Car GPS is the GPS receiver receives GPS satellite signals (3 or more), get the point latitude and longitude coordinates, speed, time and other information, get the positioning information through the satellite, if the GPS terminal is a navigation terminal, then it directly to this positioning Information is interpreted as latitude and longitude and becomes an icon displayed on an electronic map, which is the starting point for navigation. From the starting point to the destination, it is calculated by the chip in the navigation terminal. 1. 2 navigation process The moving target receives the GPS satellite signal and solves the location information of the location. The location information is transmitted to the cellular base station through the wireless signaling channel. The cellular base station receives the information transmitted by the mobile target and transmits the data information to the monitoring center through the short message center. Targeted monitoring of moving targets. The monitoring center executes relevant monitoring instructions (such as: inquiry position instruction, interception instruction, power-off instruction, etc.), and transmits the signal to the cellular base station through the short message center. The cellular base station modulates and transmits the monitoring instruction information, and transmits the signal to the moving target through the signaling channel. The mobile target receives the information transmitted by the cellular base station and executes the relevant instructions. 1. 3 wireless communication principle The GPS system is only a single positioning system, and it needs to combine the communication network system such as GSM to achieve the transfer of positioning information. GSM signal coverage, signal stability, is a good resource for wireless communication, GSM traditional data communication methods, including short message SM mode and DATA mode. The SM mode has the disadvantages of long delay (typically 6 8 s), blocking of the channel, etc.; the DATA mode has disadvantages of long dialing time (about 10 s) and high communication costs. 2 system function design 2. 1 navigation positioning module This module is mainly based on the known path of navigation, a simple string representation of navigation information, the actual application can be used to represent some of the icons, such as navigation information can be the first 5 m turn right. This module mainly includes real navigation and analog navigation. 1 is a navigation flow chart. 2. 2 path optimization module After choosing the starting point and the ending point, find the optimal or fastest path between them. The optimal path is essentially a shortest path, but its right is not a mileage, but it is a time-consuming journey. If a road section with a long principle is a fast road, it will take the least time. The fastest (optimal) path is made up of the least time-consuming path set. 2 is the module flow chart. 3 Empirical Analysis 3. 1 initial state Use an ordinary GSM mobile phone as a simple GPS installed in the car. Place the GPS-equipped van on the playground of the Jiangning Campus of Hohai University. The area is empty, GPS will not be affected by the surrounding buildings, and ephemeris data can be better received. A notebook computer is arranged as a central controller at the Drum Tower Campus of Hohai University. The central controller and the on-board GPS interact with each other via a GSM wireless card to obtain positioning signals and transmit control commands. Open the GPS device on the car and check whether the GPS communication is normal. The ephemeris data is represented by a string of characters, including the accuracy, latitude, speed, direction, and number of visible satellites. The main operations are as follows: Open the map file, start GPS, GPS connection is successful, and locate ephemeris data. Before the GPS connection works, it is necessary to set the GPS communication parameters, that is, to set how the GPS signals transmitted through the short message are interpreted as data strings that can be read by the control center. Here, first set the port number to pass the signal from a port to the computer. The port number uses COM 8, the baud rate is set to 9 600, and the check stop bit is generally one. Then set the GPS protocol format. The Wanderer GPS device we use has a special communication protocol. All operations of the vehicle and the monitoring center are completed through the GSM short message. When sending and receiving information, the basic GSM short message sending and receiving protocol must be followed and the PDU must be used. The format and the text mode are invalid. The content of the PDU packet is an agreement. When prompted GPS connection is successful, you can observe the ephemeris data at the starting point of Hohai University GPS status: latitude 118 45 5'11", longitude = 32 3 3'751", speed = 0. 00, direction = 321. 64, the number of visible satellites is 5. 3.2 Experimental results We started the test from the southern gate of the Jiangning campus and went back to the south gate along the laboratory hall, the agricultural water test field, the west playground, the turbine sculpture, the Science Building, the Wenke Building, the East Lake, and the library. At the GPS default data return frequency (a data string is transmitted every 10 s), 35 positioning points are sampled. Displayed on the control center electronic map, such as 3. 4 Error Analysis Because the accuracy of the map used is not enough, in order to verify the data accuracy, this paper uses line data to overlay the remote sensing image. As can be seen from the 4th, the test route can generally reflect the actual running track of the vehicle and eliminate the vehicle in the map. Large error phenomenon on the roof and on the river. However, the data deviated from the road near the West Playground and Science Building. On the one hand, due to the accuracy of navigation-grade GPS, there is a certain amount of error and the number of measurement points is not sufficient; on the other hand, it may be the experiment of agricultural laboratory equipment and science building of West Campus. Indoor electronic devices cause some interference with the signal, but in terms of navigation use, navigation does not affect the use. From the aspect of speed measurement, the system tests the error of the vehicle speedometer. The actual test is: the test vehicle has a constant speed of 30 km/h and the navigation is 32 km/h. The preliminary analysis is because the vehicle is old and the speedometer on the vehicle may have errors. Rather than GPS error. Some minor problems were encountered in the test. The ephemeris data was displayed normally, but it was always displayed during the navigation that the GPS was not connected. The GPS was normal but the navigation was normal. The preliminary analysis was that there was a problem with the receiving module. When the GPS is set to start, the set port will select the COM 8 system to display the data successfully after trial and error, and the GPS will only display the corresponding data after successful startup. During the test test, the GPS signal will decrease or increase according to the status of nearby buildings. When the map is a supermap, the map can be accurately displayed based on the accuracy and latitude. 5 Conclusion This article has completed the development and design of the navigation system based on GPS and the installation and debugging. Through the use of the GPS/GSM vehicle navigation system, several functions have been realized to enable real-time location search for the location of each networked vehicle; a wide range of information can be obtained through the connection between the center and other information systems and disseminated to each person. Users, to maximize the development and use of limited investment information publishing capabilities.
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