Design of Public Transportation Information Platform System Based on ZigBee

    In recent years, with the rapid development of cities in China. The number of urban population and the number of private cars owned by citizens have increased year by year, making urban traffic congestion worse and worse. The serious traffic congestion has become a common problem faced by large and medium-sized cities in China. The problem of difficulty in taking a bus caused by the congestion has troubled everyone, and the environmental pollution caused by it is also very serious.

    According to the overall level of research on vehicle positioning technology at home and abroad, it can be concluded that the existing positioning technologies have their own advantages and disadvantages. Through the current research on vehicle positioning technology, it can be known that the best solution is to select the data information of multiple systems and then use appropriate algorithms to obtain the best solution in a certain sense. At present, cities are developing rapidly, people are increasingly dependent on public transportation, and the requirements for the quality of transportation services are getting higher and higher. If the arrival information and vehicle information of the bus can be notified to the waiting people in a timely and accurate manner, it will play an important role in alleviating the congestion of the station personnel during rush hour. The information prompt system installed on the bus stop sign will provide the waiting people with the arrival time of the upcoming bus and the personnel on the bus. At the same time, they can also know the approximate arrival time of the next bus, so that the waiting passengers can prepare in advance according to their needs, providing convenience for passengers.

1 System Design

    The system uses ZigBee wireless sensor network technology to timely and accurately reflect the specific location of the bus to the bus dispatch station computer system and publish it to the driving route station in a timely manner, so that passengers and dispatchers can have a grasp of the driving status and distribution of the buses on the current route. Passengers can understand the driving information of the current vehicle; dispatchers can make reasonable arrangements and dispatch according to the real-time operation data of the vehicle. When an emergency occurs (such as traffic jams, vehicle damage, etc.), the dispatch center can make more reasonable dispatch arrangements and effectively avoid the phenomenon of early departure of bus drivers. The

    intelligent bus system can estimate the time to arrive at the next stop based on the location of the vehicle and the average speed of the vehicle. The location information of the bus is transmitted to the bus stop through the ZigBee network and displayed to passengers through the electronic display screen, so that passengers can know the information of the vehicle they want to take at any time; at the same time, the location information is finally transmitted to the dispatch center through the forwarding between ZigBee nodes for dispatch personnel to dispatch and allocate vehicles. The vehicle positioning and tracking technology applied in this system can understand the passenger flow distribution on the route, provide a basis for the formulation of the driving schedule, and at the same time, it can effectively

solve the current situation of bus operation and improve the level of vehicle management.

2 System Hardware Design

    The hardware platform of the lower computer of the intelligent bus system consists of CC2430/2431 chip, gateway system, wireless reference node and positioning node, and adopts wireless positioning mechanism to locate the moving vehicle and collect and forward the positioning data.

2.1 ZigBee Wireless Positioning Microcontroller CC2430/CC2431

    The CC2430/CC2431 chip is developed based on the CC2420 chip architecture, and integrates the microcontroller, memory and ZigBee RF front end on the chip, as shown in Figure 1. It mainly consists of an 8-bit MCU (8051), 32/64/128KB programmable flash memory, 8KB RAM, analog/digital converter (ADC), timer, AES128 co-processor, 32 kHz crystal oscillator with sleep mode timer, watchdog timer, power-off detection circuit, power-on reset circuit and 21 programmable I/O pins.

2.2 Gateway system

    The gateway system includes a baseboard and a CC2430 ZigBee module. The baseboard has a graphic Chinese character LED LCD display, a ZigBee wireless module interface, an adjustable resistor, an LED, a keypad, a power interface, and an RS-232 interface. [page]

2.3 Wireless reference node and positioning node

    The module contains CC2430/CC2431, which is a ZigBee wireless network module that complies with the IEEE802.15.4 standard. The CC2430/CC2431 module has the physical layer and hardware layer of ZigBee/802.15.4, and can realize wireless communication of data through the physical layer and the media access control sublayer.

2.4 ZigBee wireless positioning system

    The ZigBee wireless positioning system consists of two parts: a wireless positioning network and a host computer monitoring software. The wireless positioning network nodes in this system use the CC2431 chip with hardware positioning engine function and the CC2430 chip with routing function produced by TI/Chipcon. The wireless positioning network is mainly composed of terminal nodes, reference nodes and gateway nodes.

3 System software design

3.1 Design of the lower computer of the intelligent public transportation system

    The overall design of the intelligent public transportation system structure is shown in Figure 2. The CC2431 chip with the positioning engine function is deployed on the bus. At this time, CC2431 plays the role of the terminal node in the entire wireless positioning network. The CC2430 chip is deployed on both sides of the bus line and on fixed transportation facilities such as bus stops and street lights. CC2430 plays the role of a reference node in the wireless positioning network. The gateway node is deployed in the dispatch center and connected to the server of the dispatch center through the RS232 serial port data line. First, the reference node automatically forms a network system with self-organizing characteristics and starts to send its own position coordinate information and RSSI value to the terminal node. After the constantly moving terminal node receives the information of the reference node closest to it, it calculates its own coordinates through its own positioning engine and sends it to the gateway node in the network. After receiving the data, the gateway node uploads it to the upper computer for further processing. If it is necessary to dispatch and manage the bus, the dispatch center can issue instructions to direct the dispatch of the vehicle.

3.1.1 Workflow of terminal nodes in intelligent public transportation system

   The nodes in the intelligent public transportation system include terminal nodes, reference nodes and gateway nodes. Among them, the terminal node is a positioning node. After receiving the RSSI values ​​of all reference nodes in the positioning area, it calculates its own coordinate position through the positioning algorithm. The coordinate position of the reference node is a fixed value, but it does not participate in the positioning calculation. A positioning area usually consists of 8 reference nodes. CC2431 is used as the positioning node, CC2430 and the network expansion board are combined to form a gateway system, and finally connected to the computer through the serial port on the expansion board. The terminal node uses the RSSI positioning algorithm to calculate its own coordinate position based on the RSSI value sent by the reference node in the positioning area. Figure 3 is a diagram of the terminal node workflow.

    After sending a connection request in the network, the terminal node communicates with the reference node closest to it, and calculates its own coordinate position through the coordinate value and RSSI value of the reference node and according to the input parameters (A, N). This coordinate information is sent to the gateway node and finally transmitted to the server of the dispatch center through the RS232 serial port data line.

3.1.2 Design of the network layer of the intelligent public transportation system

    The network layer of the intelligent public transportation system is mainly responsible for the functions of data transmission such as networking and routing. In the network of the intelligent public transportation system, there are mainly three types of data: data sent from the bus to the central node, data sent from the platform node to the central node, and data sent from the central node to the platform node.

    The most important function of the network layer is to complete data forwarding. The network layer data service entity service access point completes the transmission of application protocol data units (APDUs) between peer application entities; the network layer management service entity service access point completes the transmission of command frames between the upper layer and the network layer management service entity. [page]

3.2 Design of system host software

    The host software of the intelligent public transportation system is developed using the Visual C++6.0 platform. The host software is divided into serial communication module, data receiving module, data processing module, data display module and data storage module. After the data is transmitted to the PC through the RS232 serial port data line, the host software completes the display and processing of the data.

    The intelligent public transportation system consists of two parts: the lower computer and the upper computer. The lower computer mainly includes hardware modules CC2431 and CC2430, which transmit data through the wireless positioning network to avoid the trouble of wiring. The upper computer is developed using VC6.0, has a friendly interface, and is a data monitoring and storage center. As shown in Figure 4.

4 Test

    The human-machine interface is mainly used to complete information interaction with the user. Through the display of the interface, the vehicle information received by the serial port is displayed to the user. The user can effectively manage the operation and scheduling of the vehicle by analyzing the information. Therefore, the design and implementation of a friendly and convenient human-machine interface is very important in the development of this system. The completion of the entire framework of the system and the human-machine interface makes the subsequent development work more organized.

    Figure 5 is the vehicle information query interface of the intelligent bus system. From the figure, you can see the vehicle ID, which line it is currently on, and how many stations it has passed.

    Figure 6 is the route information query interface of the intelligent bus system. From the figure, we can see the route name, platform number and platform name.

    This paper designs the host computer software and divides the overall functions of the system. It analyzes and discusses the communication protocols, databases and modules used in the system, designs a more feasible monitoring system and explains the key technologies in the system. Finally, after the system is implemented, the function test and simulation test of the host computer are carried out.



5 Conclusion

    ZigBee is a low-rate, low-cost and high-reliability wireless communication technology. This paper aims at the current congested traffic problem and analyzes the environment of the current public transportation system. Finally, it designs and implements an intelligent bus system platform based on ZigBee technology. The system can accurately transmit the specific location of the bus to the dispatching center and publish the data to the electronic display screen of the platform in time through the dispatching center, so that passengers and dispatchers can timely grasp the specific location of the bus. The real-time monitoring of the vehicle by the dispatching center can effectively complete the dispatch and arrangement of the vehicle. The experiment verifies that the system can operate stably and efficiently and has certain application value.