Logistics transportation vehicle monitoring system based on GPS and CDMA

　　The logistics industry has developed rapidly in recent years, and a design scheme for a logistics vehicle monitoring terminal based on GPS (Global Positioning System) and CDMA (Code Division Multiple Access) technology was proposed. The S3C2440 A ARM chip is used as the main control chip, and the appropriate GPS module and CDMA module are selected for hardware design. The study analyzed GPS and CDMA technologies. The GPS serial port receiving program and the wireless communication program between the terminal and the monitoring center are designed on the WinCE 5.0 platform. The results show that the system operates stably, the data refresh time is less than 3 s, and the GPS position drift value is less than 20 m.

　　Although various logistics, transportation and warehousing enterprises have accumulated rich practical experience in the long-term development process, the real-time monitoring of vehicle dynamic information has not been perfectly solved. For example, the information feedback is not timely, accurate, and incomplete, etc. The problem has resulted in a huge waste of transportation capacity and high operating costs. Using GPS to manage and monitor logistics vehicles and logistics objects has become a development trend. In view of the above situation, this paper studies the logistics vehicle monitoring terminal and proposes an overall system architecture based on GPS+GIS+CDMA. The system integrates Global Positioning System (GPS), Geographic Information System (Geographic Information System, GIS) and CDMA (Code Division Multiple Access) wireless communication technologies.

　　1 Overall system design

　　The logistics transportation vehicle monitoring system based on GPS and CDMA consists of a vehicle monitoring terminal, a data transmission network and a monitoring center. The data transmission network consists of CDMA network and Internet.

　　Through the GPS satellite network, the vehicle terminal can accurately position logistics vehicles and logistics objects, access the Internet through the CDMA wireless network and link to the monitoring center server, and transmit the longitude and latitude, speed, heading, altitude, time and other GPS of the logistics vehicle to the monitoring center in real time. Data information, the monitoring center can display and query various vehicle information on an electronic map with geographical information processing and query functions, and monitor the vehicle operating status in real time.

　　In addition, the monitoring center also has the function of communicating with vehicle-mounted terminals, which can dispatch logistics transportation vehicles in real time and handle emergencies in a timely manner, and is suitable for various logistics and transportation fields.

　　2 Terminal hardware design

　　The logistics vehicle terminal hardware structure designed in this article consists of S3C2440A, JTAG on-chip debugging interface, video interface, audio interface, reset circuit, CDMA wireless communication module, GPS module, power circuit, LCD touch screen, keyboard, etc., with external SDRAM, NAND FLASH, NOR FLASH is used as an external memory, and its hardware structure is shown in Figure 1.

　　2.1 CPU selection

　　2.2 CDMA module interface design

　　The terminal uses Huawei EM200 CDMA1X module. The module's working frequency band is 800 MHz, the maximum transmit power is 0.25 W, the receiving sensitivity is less than -106 dBm, the working voltage is 3.3~4.2 V, and it integrates rich resource interfaces such as UART, UIM card, and antenna. Supports standard AT command set. The ultimate working temperature is -30℃～+75℃, and the working temperature range is wide, suitable for various logistics and transportation environments.

　　S3C2440A has 3 UART serial ports. The EM200 module and S3C2440A are connected through serial port 1. Because the input and output of both are TTL levels, they can be connected directly without level conversion. Among them, the EM200 module

The pin is the data sending end and is connected to the RXD end of S3C2440A; the EM200

The pin is the data receiving end and is connected to the TXD end of S3C2440A, thereby realizing data transmission and reception between the two. The connection diagram between Huawei EM200 CDMA1X module and S3C2440A is shown in Figure 2.

　　Among them, the TXD0, nRTS0, and DTR pins of S3C2440 pass through three 1 kΩ resistors and the EM200 pin respectively.

pins are connected to prevent excessive current from causing damage to the chip.

　　2.3 GPS module interface design

　　The GPS module is the key to accurate positioning of the terminal and the core of the terminal design, so this terminal selected the SIFEIII generation GS-15B module of Gstar Company.

　　GS-15B is a high-efficiency, low-power consumption intelligent satellite receiving module. It uses the MT3329F satellite positioning receiving chip designed by Taiwan MediaTek Technology Co., Ltd. and is a complete satellite positioning receiver. At the same time, it has a full range of functions and can meet the strict requirements of professional positioning and industrial-level needs. Built-in GPS antenna, using MTK high sensitivity, low power consumption chip MT3 329F. It has the ability to quickly locate and track 32 satellites. Ultra-small in size, the chip has 200,000 built-in satellite tracking operators, which greatly improves the ability to search and calculate satellite signals. Supports NMEA-0183 v2.2 version specification output. The receiving sensitivity is -157 dBm, the operating temperature is -40℃~85℃, TTL level output, the working voltage is 3.3~5.0 V, the cold start positioning time is only 42 s, and the average positioning accuracy is 10~15 m. It not only meets the terminal's demand for high cost performance, but also meets the terminal's demand for precise positioning.

　　The interface connection diagram between S3C2440A and GS-15B is shown in Figure 3. The terminal uses serial port 2 of S3C2440A to connect to the GPS module. In order to enhance the driving capability, two 100 kΩ pull-up resistors are added to the TXD1 and PXD1 pins of S3C2440A. The terminal generally only receives GPS information and does not write to the GPS. Therefore, in order to protect the chip, a 100 Ω resistor and a reverse diode of model MCIA148 are added between RXD1 of S3C2440A and GS-15B, thus ensuring Terminal runtime stability.

　　3 Terminal software design

　　The software part of the terminal is designed based on the WinCE 5.0 embedded operating system. WinCE is a multi-tasking, fully preemptive 32-bit embedded operating system that supports WinCE MFC, ATL, WinCE API and some additional programming interfaces and various communications. technology. The WinCE embedded operating system has the advantages of good operation interface, high real-time performance, small resource usage, rich development tools and strong technical support, which fully meets the design needs of this terminal software.

　　3.1 Terminal software design process

　　First, power on the system, start the bootloader, load the WinCE kernel, and start the WinCE embedded operating system. Then initialize peripheral modules such as CPU, LCD, GPS, CDMA, etc., and then load the serial port driver and network protocol. If the loading is successful, the user application will be executed. If the loading fails, it will return and reload the serial port driver and network protocol. The user applications of the terminal include: CDMA wireless network access program, network data transmission program, GPS serial port receiving program, etc. The terminal software design flow chart is shown in Figure 4.

　　3.2 CDMA wireless network access procedure

　　The terminal controls the CDMA module through AT commands to implement wireless network access and network data transmission.

　　After the system is running, first initialize the CDMA module, set the baud rate to 115 200 b/s, and then enter the dial-up waiting state. The terminal logs in to the network through PPP dial-up connection. The access number is 777, and the user name and password are both card. After confirming successful login to the network, the GPS serial port receiving program and network data transmission program are called, and the terminal's GPS positioning information is sent to the monitoring center in a scheduled manner.

　　The AT commands and return values ​​for establishing PPP (point-to-point protocol) connections are as follows:

　　3.3 CDMA wireless network communication program

　　After the terminal is connected to the Internet through the CDMA network, the wireless network communication program uploads the GPS data analyzed by the terminal to the monitoring center through Internet. This terminal software is designed to use stream format sockets for network communication, corresponding to the connection-oriented TCP protocol in the TCP/IP protocol. The network data transmission program is programmed using the client/server mechanism. The terminal (client) process is controlled by the user; while the monitoring center (server) process resides on the host and runs continuously, waiting for the terminal connection request to enter.

　　The network communication program flow of the monitoring center is as follows: 1) Use the socket() function to create a socket and assign a value to the socket address structure; 2) Use the bind() function to bind the socket to the local IP address and port number, and select static IP address; 3) Use the listen() function to listen for connection requests on the socket; 4) Use the accept() function to receive the terminal connection request, generate a new socket and descriptor and connect to the terminal, using the new socket Send and receive data; 5) Use the fork() function to spawn a new child process to communicate with the terminal, and the parent process continues to listen to other requests. This can avoid the problem that after a terminal establishes a connection with the monitoring center, the monitoring center can no longer communicate with other terminals.