Passengers' service demands extend beyond the journey itself, encompassing both before and after travel; they require not only transportation but also quality and comfort. These multi-layered and diverse needs are beyond the capabilities of traditional operating models and dispatching methods; only the implementation of intelligent public transportation systems can fundamentally address these issues. The implementation of intelligent public transportation systems not only brings significant benefits to passengers and enhances the city's image but also saves public transportation companies substantial operating costs and improves their scientific management. Therefore, the construction of intelligent public transportation systems yields significant social and economic benefits.
The intelligent public transportation system consists of the following parts:
1) Vehicle-mounted equipment subsystem, abbreviated as "vehicle terminal";
2) Intelligent electronic station sign system;
3) Public transport management system.
The paper mainly focuses on the vehicle-mounted terminal, a subsystem of in-vehicle equipment.
1 System Overall Scheme Design
This paper studies a smart bus terminal based on GPS and 3G; in short, it studies the onboard terminal equipment located on the vehicle body. The research is mainly divided into three parts: video surveillance; GPS positioning; and transmission via existing 3G networks.
The video surveillance system consists of two cameras installed on the exterior of the bus and four cameras installed inside. One camera is installed at the front and one at the rear of the bus to monitor traffic conditions and provide strong evidence for determining liability in the event of a traffic accident. Inside the bus, one camera is installed at the driver's location to monitor for violations such as making phone calls or chatting; one camera is installed at the fare box to monitor for fare theft; and one camera is installed in the middle of the bus to prevent passengers from staging accidents and extorting money, as well as theft, thus reducing the crime rate on buses. One camera is installed at the exit door to observe passenger disembarkation, ensuring all passengers have disembarked and preventing fare evasion such as boarding through the rear door.
The GPS positioning component enables comprehensive navigation functionality. By using the GPS global positioning system to determine the bus's location and transmit real-time location and traffic information to a PC monitoring terminal, it plays a crucial role in vehicle dispatching.
Regarding the 3G network transmission, my country's 3G network has matured significantly in recent years, enabling efficient transmission of video information. This system uses the 3G network to transmit video and CPS information collected on the bus to the control terminal, achieving full-process monitoring of the bus during operation. The overall system design is shown in Figure 1.
2 System Hardware Design
In terms of hardware design, this system uses the ARM S3C2440 microprocessor chip as the main control chip. The system expands storage with 128MB of NAND flash and 64MB of SDBAM, allowing for better storage of video information. Peripheral expansion modules include a universal USB camera, GPS module, 3G module, and LCD display. The system's hardware block diagram is shown in Figure 2.
2.1 Selection of Main Control Chip
The monitoring terminal designed for this system requires multi-channel transmission, strong real-time performance, and low power consumption. Therefore, the main control chip selected for this system is an ARM9 processor with an ARM920T core. Since the S3C2440 chip is widely used, has abundant on-chip resources, complete documentation, and a moderate price, it was chosen as the system's microprocessor. This processor is a 32-bit RISC-based microprocessor with a working frequency of 400 MHz, which can reach a maximum of 533 MHz, meeting the system's processing speed requirements. Furthermore, this processor integrates rich communication interfaces and controllers, effectively reducing system complexity and providing a good hardware platform for system development.
2.2 Selection and Connection of Camera Module
This paper describes a dynamic video monitoring method. The selected camera is the NetEye V2000, whose image sensor and digital signal processing chip are Omnivision's OV7620 and OV511. It boasts fast imaging speed, high image quality, low cost, and good versatility. Using a USB interface, it eliminates the need for a video card, offering plug-and-play functionality, ease of use, and clear, continuous images with low pixelation. This provides a reliable hardware foundation for effective video recording. The NetEye V2000 camera connects directly to the USBHost interface integrated on the CPU via its USB interface.
The OV7620 is a highly integrated, high-resolution color image sensor. It has a resolution of 640x480 and a transmission rate of up to 30 frames per second. The OV7620 is controlled using the SCCB (Serial Camera Control Bus) protocol, allowing for settings adjustments and image data readout via its SCCB interface.
The OV511 is the main control chip for the camera. Its on-chip high-performance compression engine can achieve an image compression ratio of 7:1, ensuring fast image transmission from the image sensor to the main controller.
2.3 GPS Module Selection and Connection
The GPS module used in this system is the HOLUX GB-87 module. This module supports the NMEA0183 protocol, supports V3.3-V5.5 voltage input, TTL interface level, and configurable baud rate. In this system, the GR-87 module is connected to the motherboard via a 6-pin ribbon cable. Pin 1 is the power input pin, connected to a 5V power supply; pins 2 and 3 are for data reception and transmission; and pin 5 is grounded. During operation, the GPS module's serial port 2 communicates with the main controller S3C2440. By setting the module to periodically output GPS positioning data, the main controller processes the GPS data, extracting useful information such as latitude, longitude, and time, providing reliable data for automatic station reporting and punctuality assessment, ensuring the implementation of these functions.
2.4 Selection and Connection of 3G Modules
Based on different wireless interface technologies, existing 3G technologies can be divided into China Unicom's WCDMA technology, China Telecom's CDMA2000 technology, and China Mobile's TD-SCDMA technology. Considering factors such as transmission bandwidth, network stability, and practicality, this system adopts China Telecom's CDMA2000 as the wireless network transmission and ZTE's MC8630 module as the video data transmission module. The MC8630 module has functions such as voice, SMS, data services, and GPS. It operates on the 800MHz frequency band and, through dual-antenna diversity and equalization technologies, achieves a maximum uplink rate of 3.1 Mbit/s and a maximum downlink rate of 3.1 Mbit/s. The MC8630 module can be connected to the MIN2440 (a development board with S3C2440 as the main chip) processor via a USB interface to realize the packaged video data transmission.
3 System Software Design
Currently, common embedded operating systems include WinCE, Linux, and VxWorks. Among them, the Linux operating system has completely open source code. Due to its advantages such as high efficiency and stability, abundant network resources, small kernel, fast execution speed, and good portability, it is widely used in the field of embedded systems. Therefore, the embedded Linux operating system was chosen as the software development platform for this system.
In terms of software design, the first step is to establish a cross-compilation environment between the microcontroller and the PC to compile the bootloader and the Linux kernel. Then, the bootloader is ported; the Linux kernel is configured and compiled; and the root file system and low-level drivers are created. Finally, upper-level applications are written to perform functions such as image acquisition, GPS information collection, and 3G transmission. The following sections detail the design principles of several key programs.
3.1 Image Acquisition Program
For video capture, this paper uses the NetEye V2000 camera, which is a camera with the OV511 as its main control chip. It was chosen because the Linux kernel includes the OV511 driver, eliminating the need to write a custom camera driver; it can simply be selected during kernel customization, saving development time.
After the Linux system boots normally, plug in the V2000 camera. If the driver loads successfully, a device file named device0 will be created for the camera in the /dev/v41/ directory. Upper-level applications can then access the camera through this device file to capture images. With the embedded system platform successfully built, to achieve real-time image acquisition, an image acquisition program needs to be implemented using the V4L (Vidio for Linux) programming interface. Considering the large amount of 640x480 RGB image data captured by the camera, the image compression function put_image_jpeg is used to convert the image to JPEG format. This reduces the NandFlash space required for storage and also reduces transmission costs and ensures successful transmission when sending data back to the monitoring center via the 3G network.
3.2 GPS parsing program
The HOLUX GR-87 GPS receiver module outputs data in a format conforming to the NMEA.183 standard. The NMEA.183 protocol is a serial communication data protocol developed by the National Marine Electronics Association (NMEA). All input and output information is presented as a single line of ASCII characters. Each message is called a sentence, and each sentence begins with a "$" and ends with a newline character () followed by several fields separated by commas.
Because the GPS module's settings are lost upon power failure, it must be initialized every time the system starts. The module is set to output GPS information once per second. After system startup, the module receives GPS information, parses it, and calculates the actual distance by comparing the parsed latitude and longitude with the station information stored in the data area. If the distance reaches a threshold, a GPS station reporting interrupt is initiated. This GPS module's receiver follows the NMEA.0183 protocol and can output data frames in various formats, all beginning with "MYM". The output data uses ASCII characters and includes information such as latitude, longitude, speed, date, heading, and satellite status. This system uses only the $GPRMC positioning data frame format. After system startup, the GPS module is configured via serial port. Since the system does not have high real-time requirements, the GPS is set to output RMC data once per second. The approach to extracting GPRMC statements is to set up a data buffer, placing all received GPS data into this buffer. When the buffer is full, it checks if a GPRMC positioning statement has been received; if not, GPS data is re-received. If a GPRMC location statement is found, it is necessary to determine whether the position of the statement in the buffer is more than 62 bytes away from the maximum number of bytes in the buffer (because the GPRMC location statement required by this program contains 62 bytes). Then, relevant latitude, longitude, time, and speed information are extracted through multiple programs and processed by the data processing thread. The running process is shown in Figure 3.
3.3 3G Module Parsing Program
The MC8630 module driver can be generated through cross-compilation of the driver source code. The process of loading the MC8630 module and establishing a dial-up connection is as follows:
1) Before compiling, you must first ensure that the compilation environment for compiling the driver and the kernel is the same, that is, you need to use the same version of the cross-compilation tool (the Linux version in this system is 2.6);
2) Modify the driver source code Makefde file, including adding the kernel source code directory and compilation tools;
3) After compilation with Make, ztemt.ko is generated;
4) `insmod ztemt.ko` generates four device nodes: `/dev/ttyUSB0`, `/ttyUSB3`, and `/dev/ttyUSB0`.
5) `mknod /dev/ttyUSB0 c 188 0`, create a device node;
6) Write Linux dialing scripts, chat configuration files, and account/password configuration files;
7) Add kernel options to compile a kernel that supports the PPP protocol;
8) `pppd call evdo` establishes a dial-up connection, and `ifconfig` checks if the network is connected.
9) ppp-off interrupts the connection.
4. Conclusion
The intelligent bus terminal designed in this system adopts advanced 3G/GPS technology. By collecting, transmitting and processing information on the operation of buses, it realizes real-time monitoring and dispatching of bus operations, quickly adjusts the operating status of buses, improves the efficiency of vehicle operation, and enables the optimal utilization and allocation of bus resources, thus achieving intelligent bus operation.
