GPS graphics navigator Based on GPRS network

By studying GPS navigation and the Integrated Navigation Technology Based on GPRS wireless network data transmission, the design scheme of GPS graphics navigator unit based on GPRS network is presented. It consists of GPS receiver, ARM microcontroller, GPRS wireless module, large-capacity flash storage chip, and large screen TFT color LCD screen. This graphic navigation device can help users obtain excellent geographical information navigation help and monitor important information.

Introduction

With the development of science and technology in recent years and people's requirements for communication and navigation technologies, the positioning and navigation technology based on global positioning system (GPS) positioning technology has developed rapidly. GPS navigation and positioning technology has been widely used in many industries, such as transportation, navigation, and security. However, few GPS navigation monitoring devices that are currently in use transmit important data over wireless networks to the monitor devices. Most of the other devices with the data transmission function only transmit and receive important data by sending short messages. However, because short messages have the disadvantages of uncertain delay, slow speed, and easy loss, this reduces the stability of the entire system.

The system sends important data based on the new GPRS wireless network. The large screen TFT color LCD screen is used as the map display device, this greatly enhances the visualization of positioning and the stability of data transmission functions.

1. SYSTEM COMPOSITION AND FEATURES

The core technology involved in this navigation device is the universal grouping wireless service GPRS and the Global Positioning System GPS. The core modules of these two systems are briefly described below.

GPS (global positioning system) is a national defense Navigation Satellite System of the United States. It is a global, around-the-clock, full-day, high-precision navigation and time delivery system. The 24 satellites are located in six 55 ° orbital planes with a height of 20 182 km and a cycle of nearly 12 hours. Satellites use two L-band frequencies to transmit one-way ranging signals. Different satellites use code division multiple access. It is a dual-purpose system that provides two levels of services. The GPS system provides global aircraft, ships, tanks, ground vehicles, infantry, missiles, and space aircraft with 24x7, continuous, real-time, and high-precision 3d positions, 3D speeds, and accuracy. time, therefore, it has extremely high military value and prospects for civil use.

GPRS (General Packet Radio Service) is a wireless group Switching Technology Based on the GSM system. It provides end-to-end and wide-area wireless IP connections. In layman's terms, GPRS is a high-speed data processing technology that transfers data to users in the form of "grouping. Although GPRS is a transitional technology from the existing GSM network to the third generation mobile communication, it has significant advantages in many aspects. GPRS is the standard for grouped data in the European Telecommunications Association's GSM system. It uses channel bundling (currently, GPRS can be bundled in one carrier frequency or eight channels) and data rate enhancement methods to achieve high-speed access, theoretically, up to 115 kbps of air interface transmission rate can be provided, so that a number of mobile users can share a wireless channel at the same time, a mobile user can also use multiple wireless channels. Users who actually send or receive data packets only occupy a small part of network resources, and the network capacity is occupied only during actual transmission. The fundamental difference between GPRS and the existing GSM voice system is that GSM is a circuit switching system, while GPRS is a group switching system. Therefore, GPRS is particularly suitable for intermittent, sudden, or frequent, small amounts of data transmission and occasional transmission of large data volumes. This feature is suitable for most mobile devices and data transmission requirements.

GPS-GPRS Positioning System vehicle terminal Composition 1 shows.

Figure 1

 

The general workflow of the navigator is as follows: first, the terminal navigation device obtains its own geographic location information and ancillary information (such as the travel speed and time) through its own GPS receiving module ). Then, the map corresponding to the current location is displayed on the TFT color LCD screen by map of the built-in massive storage device, in addition, it displays its own status (such as speed, time, and message received from the control center), and sets its own GPRS module to enable dial-up access to the Internet. Next, you can transmit the specific information obtained through the GPS receiving module to the specified network server.

The network server monitors the current location, speed, and other information of the monitored terminal device in real time through a specific host computer software or corresponding transmission protocol, the Controlled Terminals can be controlled through the network to achieve two-way data transmission between mobile terminals and the monitoring center, and monitor the running status, security status, and technical status of the controlled terminals.

2. Navigation System principles

The principle of the entire navigation system is shown in figure 2. Among them, the core controller uses at91sam7s64 Based on the ARM7 kernel; the GPS receiving module adopts timlh of Swiss ubrov, and the signal receiving capability is strong; the GPRS module uses the G20 wireless module of Motorola, the feature is embedded with the TCP/IP protocol, which is simple to use and stable in performance. The display part adopts the 8-inch TFT color LCD screen produced by the sharp company. by displaying the color map of the current position, achieve good visualization. External Storage devices use large-capacity flash storage bodies produced by Samsung. The advantage is that they are inexpensive and have simple interfaces with controllers (high-speed SPI bus ).

Figure 2

The main functions of this navigation terminal are as follows:

① The end user queries the current location;
② After obtaining the current geographic location information, the corresponding map area is displayed on the tft LCD screen;
③ The navigation terminal can send its own information to a specified network server, such as its geographical location and status;
④ The navigation terminal receives control commands sent by the network server for corresponding control;
⑤ End users can call through the GPRS module.

The system works as follows:

The core control part of the navigation terminal is the at91sam7s64 microcontroller based on the ARM7 kernel. Its core is to read the positioning data of the GPS receiving module and control the GPRS module, this includes connecting to the Internet, sending data to the network monitoring server, and reading the data sent from the server. Finally, it controls the flash storage body and obtains the current geographical location information, read the corresponding part of the map stored in the flash storage body and display it on the TFT color LCD screen.

The controller controls the GPRS module through the serial port uart0 and sends the corresponding at command to control the G20 module, such as connecting to the Internet, sending information to the server, receiving data, and making phone calls. The key commands are as follows:

At + mipcall = 1, cmnet // create a wireless GPRS Link
+ Mipcall: 10.103.201.135
// Return the local IP address (Note: After the GPRS module dials the internet, it will obtain a unique IP Address Provided by the server. Here, 10.103.201.135 is used as an example)
At + mipopen =, "10.103.67.30", 1
// Open a socket. The local port is 2000 and the target IP address is
// "10.103.67.30"
OK
+ Mipopen: 3000 // The returned destination port is, and the protocol type is UDP
At + mipsend = 1, "41424344" // send four letters "ABCD" to the server. Here, the "ABCD" character is used as an example to replace the data to be sent.
+ Mipsend: 1,1367
OK // sent successfully
At + mippush = 1 // prepare to receive data
+ Mippush: 0
OK // The data is successfully received.
+ Miprudp: 211.139.189.180, 47280,1, 5, 5152535455 // receives the "qrstu" character from the server

The data reception of the GPS module is achieved through the serial port uart1, And the positioning data is obtained from the serial port of the module by setting the baud rate specified by the GPS module. The common command format for GPS is nmea0183, and the most important information is a set of positioning information. If the communication between the GPS receiver and the satellite is normal at this time, the data format of the positioning information that can be received is as follows:

$ Uplmc, 204700, A, 3403.868, N, 11709.432, W, 001.9, 336.9, 170698,013.6, E * 6e

The data is described as follows:

$ Uplmc indicates the shortest Data recommended by GPS;
204700 utc_time represents the standard time in the 24-hour format, in the hour/minute/second format;
A A or v a indicates that the data is "OK", and V indicates a warning. The 3403.868 lat latitude value is precise to the first four digits of the decimal point, and the last three digits n lat_dir n indicates the north latitude, s indicates the south latitude;
11709.432 Lon longitude value, accurate to the first five decimal places, the last three W lon_dir W indicates the western longitude, and E indicates the eastern longitude.

If there is no contact with the satellite, the string format is:

$ Gprs mc, utc_time, V ,...

The following is an example:

$ Gprs mc, 204149, V, 170698, * 3A

Because the only information to be received here is the positioning information, that is, the shortest Data recommended by GPS, when receiving data from the GPS module, you only need to determine whether the keyword starting with each row of data is "$ uplmc". If so, it is received.

The last step is to control the flash storage and TFT color LCD screen. Here, the CPU uses a common SPI high-speed serial bus to drive the flash storage body. You can obtain a digital color latitude and longitude map of common precision from the Local Survey Department and store it in the flash storage body, and use the ordinary I/O pins to drive the TFT color LCD screen, the positioning information obtained from the GPS module is analyzed, and then processed, and the corresponding part of the map stored in the flash storage body is displayed on the LCD.

3 System Software Design

In the entire GPS navigation system, a complete set of software systems are composed of user software, the underlying driver software of the navigator, and the server-side control software. Here, the underlying driver software of the navigator is used to explain how the software of the entire system is designed and operated.

The underlying driver software of the navigator is divided into several modules, which are composed of the main module and multiple sub-modules. Here, the use of real-time embedded system μC/OS-II, its advantage is powerful, the occupation of system resources is small, real-time response, in addition, you can easily schedule multiple tasks. HereProgramSet the task as follows:

① Ostaskcreate (systeminit, (void *) 0, (OS _stk *) & systeminit [ostaskstksiz], 4 );
// Initialization of the entire system, as the first task, including initialization of CPU, GPRS, GPS, and LCD
② Ostaskcreate (gps_get_data, (void *) 0, (OS _stk *) & GPS [ostaskstksiz], 5 );
// Read positioning information from the GPS module as the second task
③ Ostaskcreate (maid, (void *) 0, (OS _stk *) & maid [ostaskstksiz], 6 );
// Set the task of sending data to the specified network server through the GPRS module
④ Ostaskcreate (maid, (void *) 0, (OS _stk *) & maid [ostaskstksiz], 7 );
// Set the GPRS module to receive data from the specified network server as another task
⑤ Ostaskcreate (LCD _draw, (void *) 0, (OS _stk *) & LCD [ostaskstksiz], 8 );
// Drive the tft LCD to display the map part corresponding to the current geographic location area as the whole display part of the task
⑥ Ostaskcreate (flash_drive, (void *) 0, (OS _stk *) & LCD [ostaskstksiz], 9 );
// Drive the flash storage body to read the map part of the corresponding geographical location information, so as to prepare the LCD display part

After completing the modular design of the entire system software, call the osstart () function to run the entire system. From the above software composition instructions, you can understand the entire system software workflow as follows:

① The CPU obtains the current geographic location information through the GPS module.
② Using the GPS positioning information obtained just now, the CPU can obtain the map of the current region from the flash storage body, and then display it by driving the TFT color LCD screen.
③ If necessary, after the CPU connects to the Internet through dialing through the GPRS module, it sends the obtained positioning information to the specified network server or receives data from the server.
④ After receiving the control command from the server, return a response and take corresponding measures, such as stopping GPS data reception and changing the cycle of the navigation terminal sending data to the server through the GPRS network.

As shown in figure 3.

Figure 3

In actual tests, a digital color latitude and longitude map with common precision is used and loaded into the flash storage body of the navigation system. Through the actual test and comparison in the open air, the navigation system can read the current GPS positioning information and display the map of the current area on the TFT color LCD screen, the positioning information and related data sent by the navigation terminal are well received on the server where a specific network monitoring software is installed.

Conclusion

In this navigation system, its core design is very different from the traditional gpsgsm positioning system. First of all, the use of GPRS wireless network to transmit data has been greatly improved, especially its operation cost, compared with the previous methods of sending text messages through GSM network, both in terms of operation cost and reliability, compared with the traditional GPS-GSM positioning system, the positioning system is reduced by 2 orders of magnitude. Secondly, the good visual effects of this navigation system provide users with excellent navigation interfaces. In comparison, the traditional GPS Positioning System on the market only displays the current GPS positioning data, the current surrounding geographic conditions cannot be provided to users. This navigation system controls the core's high-performance microcontroller based on the ARM7 kernel. Therefore, both performance and scalability can be achieved, compared with the traditional 8-bit single-chip microcomputer as the control core, it has a considerable advantage. Currently, with the increasing demand for GPS navigation technology and the high-speed popularization of GPRS networks in China, we believe that the new generation of navigation technology combined with the two will be extremely successful.

References
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