Design of intelligent public transportation system based on wireless communication technology

introduction

Public transportation has strong advantages that cannot be matched by individual transportation. Giving priority to the development of urban public transportation systems is the best way to solve the traffic problems in large and medium-sized cities. In recent years, the intelligence of urban public transportation systems has become the main direction of public transportation research. Most of the existing trial-operated intelligent public transportation systems in China use GPS global positioning system for positioning, and use GPRS network for data transmission. The vehicle-mounted GPS module can obtain navigation positioning data such as location, direction, time, etc. in real time, and then transmit the data to the monitoring center through the vehicle-mounted GPRS module to realize the positioning and monitoring of the vehicle. The monitoring center can send the real-time information or announcement information of the vehicle to the electronic bus stop through the GPRS module of the electronic bus stop to estimate the arrival time and distance, and then display it on the electronic bus stop. Although the existing trial-operated intelligent public transportation system has a wide positioning coverage and high accuracy, it can realize the full range of vehicle positioning and monitoring. However, in the actual operation process, there are still the following shortcomings:

GPS signals may have blind spots in tunnels and viaducts;

During operation, GPS information needs to be sent to the monitoring center via GPRS, and then the monitoring center sends the display information to the electronic station sign via GPRS, so the operating cost is high;

GPRS modules are expensive. There are many buses and they all need to be installed with GPRS modules, so the hardware cost is high.

Communication between buses and bus stops cannot be achieved, and services such as advance stop announcements cannot be implemented.

1 System Overall Plan

Since Xi'an is a small city with concentrated roads and dense bus routes, the distance between electronic bus stops is mostly around 500 meters. Therefore, the monitoring center does not need to conduct real-time full-range monitoring of buses. It only needs to know the range of the bus stop signs to roughly locate the bus.

In order to absorb the advantages of the existing intelligent public transportation system solutions, overcome their shortcomings, and combine the characteristics of Xi'an city itself, this paper introduces ZigBee short-range wireless communication technology into the intelligent public transportation system, and improves the data transmission method of the GPS positioning and GPRS information transmission solutions commonly used in the existing domestic trial-operated intelligent public transportation systems. The overall architecture of the improved intelligent public transportation system solution is shown in Figure 1.

Figure 1 Overall plan of intelligent public transportation system

The system mainly consists of three parts: bus terminal, electronic bus stop terminal and management monitoring center server.

The bus terminal can locate the bus's location information in real time based on the on-board GPS module and compare it with the location information of each bus stop. When it arrives at a bus stop, the bus will automatically announce the stop with voice and display the arrival information on the LCD screen.

The electronic bus stop terminal and the bus terminal can communicate through the ZigBee short-range wireless communication network. The bus can announce the bus stop in advance. When the bus arrives at a bus stop, it will send its vehicle information, status information, etc. to the bus stop. After receiving the information from the management center, the electronic bus stop will display the location information of the bus on the electronic map of the bus stop.

The management center server and the electronic bus stop terminal can communicate through the GPRS wireless communication network. The electronic bus stop terminal processes and repackages the received bus information through the wireless networking of the GPRS module, and then sends it to the wireless network. The server side is generally a PC connected to the Internet, which can receive information on the Internet through the TCP/IP protocol, and can also send the real-time location information and announcement information of the buses on the running route to the electronic bus stop terminal. The server can manage and query information through the database to facilitate the management and dispatch of the bus company.

2 System Hardware Design

2.1 Hardware composition of vehicle terminal

The vehicle terminal hardware in this system mainly includes power module or power access module, ARM processor, RAM, FLASH, GPS positioning module, ZigBee radio frequency transmission module, video monitoring module, LCD display module, serial port and debugging module, vehicle population counting module and voice module, etc. Figure 2 shows the hardware block diagram of the vehicle terminal in the system.

Figure 2 Block diagram of vehicle terminal hardware composition

The ARM embedded processor is the core of the entire vehicle terminal, and can be connected to various functional modules through various interfaces. This vehicle terminal uses a 16/32-bit RISC embedded microprocessor S3C2410 based on the ARM920T core from Samsung, South Korea. The operating frequency of S3C2410 can reach 203 MHz, and it is mainly aimed at high-cost-effective and low-power applications such as handheld devices.

In the intelligent public transportation system, the system positioning module generally uses a GPS-OEM (Original Equipment Manufacture) board.

In embedded vehicle terminal systems, when selecting GPS modules, factors such as positioning accuracy, price, power consumption, volume, and anti-interference ability should usually be considered. Based on the above principles, this design uses LEADTEK's third-generation GPS SiRF star III7855 module to achieve positioning. The main performance indicators of this module are as follows:

There are 20 parallel channels, which can receive 20 satellites at the same time;

Positioning time: recapture time is 0.1 s, hot start <1s, cold start <42 s, automatic search less than 30 s;

The output differential accuracy can reach 10 meters, and the power consumption is less than 1 W;

The ASCII code statements of NEMA-0183 protocol can be output through RS232 interface, including GPGGA, GPGSA, GPGSV, GPRMC, GPVTG, GPGLL, etc.

Using a 5 V power supply, a DB9 interface can be connected through the TX and RX pins to communicate with the serial port of the embedded microprocessor.