Application of Wireless Sensor Network in Intelligent Transportation System
chrispeng [ad_1]
The application of intelligent transportation system (ITS) in urban traffic is mainly reflected in microscopic traffic information collection, traffic control and guidance, etc., by improving the effective use and management of traffic information to improve the efficiency of the traffic system, mainly by information collection and input , Strategy control, output execution, data transmission and communication between subsystems and other subsystems. The information collection subsystem collects vehicle and road information through sensors, and the strategy control subsystem uses calculation methods (such as fuzzy control, genetic algorithm, etc.) to calculate the best Scheme, and output control signals to the executive subsystem (usually a traffic signal controller) to guide and control the passage of vehicles to achieve the preset goals.
Wireless sensor network is a new technology that integrates short-range wireless communication technology, microelectronic sensors, and embedded systems. It is gradually being used in intelligent transportation systems and other related fields that require data collection and detection. The ZigBee technology based on the IEEE 802.15.4 specification has the following good features: ①Low power consumption, 2 ordinary AA batteries can support a node to work for 6 to 24 months; ②Strong networking capability, the network can reach up to a node, It also supports a variety of networking methods such as tree, star, and mesh; ③The transmission distance is long, the outdoor transmission distance of two nodes can reach hundreds of meters, and the transmission power can reach several kilometers; ④High reliability, with Multi-level security mode; ⑤Low cost, open simplified ZigBee protocol stack, working in 2.4GHz license-free ISM frequency band.
The wireless sensor network has excellent characteristics and can provide an effective means for the information collection of the intelligent transportation system. It can monitor vehicles in all directions at the intersection. According to the monitoring results, simplify and improve the signal control algorithm to improve the traffic efficiency. The wireless sensor network can be applied to the control subsystem and the guidance subsystem in the execution subsystem. For example, this technology can be used to improve the signal controller to realize the bus priority function of the intelligent bus system.
Construction of wireless sensor network for ITS
As shown in Figure 1, in the wireless sensor network structure, the sink nodes on both sides of the installation road form a self-organizing multi-hop mesh basic network architecture. The sensor terminal nodes dedicated to traffic information collection and each adjacent sink node form a star. Type network for communication, the final data will be aggregated to the gateway node. The gateway node can be installed as a module in the traffic signal controller at the intersection, and the collected data will be sent to the traffic control center for further processing through the signal controller’s proprietary network.
In the deployment of wireless sensor networks, convergent nodes can be installed on roadside columns, bars and other transportation facilities, gateway nodes can be integrated into traffic signal controllers at intersections, and dedicated sensor terminal nodes can be landfilled under the road or installed on the road. On the roadside, moving vehicles on the road can also install sensor nodes to dynamically join the sensor network.
Figure 1 Wireless sensor network structure for intelligent traffic information collection
Use wireless sensor network to collect traffic information
In the collection of traffic information, terminal nodes can use non-contact geomagnetic sensors to regularly collect and perceive information such as the speed and distance of vehicles in the area. When the vehicle enters the monitoring range of the sensor, the terminal node collects important information such as the driving speed of the vehicle through the magnetic sensor, and transmits the information to the next node that wakes up regularly. When the next node senses the vehicle, combined with the estimation of the vehicle’s travel time between the two sensor nodes, the average speed of the vehicle can be estimated. Multiple terminal nodes aggregate the information collected and preliminarily processed respectively to the gateway node through the convergence node to perform data fusion to obtain information such as road traffic flow and vehicle speed, so as to provide accurate input information for road traffic signal control. By installing various sensors such as temperature and humidity, illuminance, and gas detection on the terminal nodes, it is also possible to detect road conditions, visibility, and vehicle exhaust pollution.
Figure 2 Wireless sensor network deployment for traffic information collection
Application of Wireless Sensor Network in ITS
The realization of the bus priority function in the intelligent bus system requires the transformation of the existing traffic signal controller. By adding auxiliary equipment such as sensors, the traffic signal controller can estimate the time (travel time) for the bus to reach the intersection, calculate whether the bus needs to be given priority at the intersection (you can choose the number of passengers as the priority), and then select the appropriate one Priority control strategy, by adjusting the green letter ratio to give priority to public transport vehicles. The transformation of the traffic signal controller includes:
① Vehicle-mounted wireless communication terminal node;
②Integrate a wireless gateway on the cross-circuit *pass signal controller;
③Terminal nodes used for bus positioning;
④ The above functions can be realized by constructing a wireless sensor network based on ZigBee.
When approaching the intersection, the vehicle-mounted ZigBee wireless terminal node broadcasts the information of the bus. After the wireless sensor network deployed on the roadside obtains the information, the terminal node of the bus positioning tracks it to obtain the information and gathers it on the wireless sensor network gateway node. The final information of the internal connection is transmitted to the traffic signal controller for corresponding priority processing.
Design of network node and gateway node
Network node software function design
In the design of ITS wireless sensor network, network nodes need to be designed separately according to their different functions. The software functions of terminal nodes, sink nodes and gateway nodes are shown in Figure 3. Different sensors are installed at the terminal nodes for moving vehicle information collection and road information acquisition, etc. Its function realization can be realized according to the reduced function device (RFD, Reduced Function Device) standard. The terminal node and the sink node are networked in accordance with the star network, and actively communicate with the sink node when they wake up from a sleep state at a fixed time point. Information routing is completed by the parent (sink) node and the coordinator and router with routing function in the network, which reduces node power consumption and software implementation complexity. The sink node is an extension of the terminal node software function, which realizes the function of expanding the network and routing messages, allowing more important nodes to access the network. It can be designed according to the FFD (Full Function Device) standard.
Figure 3 Software functions of wireless sensor network nodes
The gateway node is the coordinator needed in the network. It is responsible for starting the network, configuring the network member addresses, maintaining the network, maintaining the binding relationship table of the nodes, etc., and is also responsible for the preliminary processing of the collected data and delivery to the traffic signal controller for transmission to the upper The first-level information center requires more storage space, computing and communication capabilities.
{$page$}
Hardware function design of network node
Figure 4 Sensor node design
Figure 5 Imote2 system structure
●Other considerations for node design
The following considerations need to be considered when designing dedicated wireless sensor network nodes for intelligent transportation systems:
① Node low power consumption design. The terminal nodes are all powered by batteries (solar storage batteries can be used).
② The node cost should be low. When deploying large-scale traffic information collection and other deployments, node cost will be the key to the project.
③Data processing and storage capacity of the node. Some nodes need to collect high-speed information and run recognition algorithms, so data processing capabilities are required. It is also necessary to consider functions such as storing programs, data, and supporting code online updates in a limited space.
④In addition, according to the needs of different application occasions, wireless sensor nodes must have different sensor interfaces and can be connected to different sensors.
Among them, energy consumption management should be considered as a key consideration. In particular, the solution of using a 32-bit ARM processor with an external RF chip needs to effectively reduce node energy consumption, and further improve energy consumption management in system-level software, such as optimizing TinyOS or embedded Linux power management functions.
Concluding remarks
More attention has been paid to the application and research of wireless sensor network technology. This article discusses the design of wireless sensor networks and other issues in conjunction with typical applications in intelligent transportation systems. With the development and maturity of technology, wireless sensor network technology can be applied in more critical situations in intelligent transportation systems, such as electronic toll collection, traffic safety and automatic driving, parking management, traffic guidance systems, etc., to further promote the development of intelligent transportation systems. developing.
●Design scheme based on TI-based CC2420 chip and ARM single-chip microcomputer
When designing wireless sensor network gateways, strong data processing capabilities are required to implement complex routing protocols and information processing. As shown in Figure 5, the imote2 node of Crossbow uses a Marvell PXA271 high-performance, low-power processor. The processor uses dynamic voltage regulation technology with a frequency range of 13MHz~416MHz, can work in low voltage (0.85V) and low frequency (13MHz) mode, and has excellent dynamic power management technology. In addition, the processor package integrates three chips 256KB SRAM, 32MB FLASH and 32MB SDRAM, reducing the size. By providing multiple I/Os, different types of sensors can be flexibly supported. The processor also supports an MMX co-processor to improve multimedia processing capabilities and can be used for voice and image processing in wireless multimedia sensor networks. Imote2 uses TI’s CC2420 ZigBee radio frequency chip, which supports 2.4GHz, 16-channel 250kb/s data transmission, and a transmission power of -24～0dBm. The effective communication distance is 30 meters, and the transmission distance can be increased by connecting an external antenna through the SMA interface.
There are a lot of wireless sensor network solutions, including the external radio frequency chip of the single-chip microcomputer and the single chip integrated radio frequency and microprocessor launched by various chip manufacturers. ZigBee radio frequency chips commonly used in node design include AT86RF230 from Atmel, CC2420 from TI, MC1319x and MC1320x from Freescale, and MRF24J40 from Microchip. In addition, chip manufacturers have introduced single-chip solutions, such as TI CC2430 extending the architecture of the CC2420 chip, integrating ZigBee RF front-end, memory and microcontroller on a single chip; Freescale’s MC1321x/MC1322x and Jennic’s JN5121/JN513x Single-chip solutions, etc.
●Based on Atmel’s AT86RF230 radio frequency chip and AVR microcontroller design
The typical terminal node and assembling node design is shown in Figure 4, using Atmel’s 8-bit RISC structure low-power ATMegal1281V MCU as the system control core. Use 512 KB AT45DB041D as external program memory. The radio frequency module uses Atmel’s AT86RF230 which supports ZigBee protocol, the RF power reaches 3dBm, and the outdoor transmission distance can reach more than 300 meters. The expansion interface of the node can be connected to analog input, digital I/O, I2C, SPI and UART interfaces. These expansion interfaces make it It is easy to connect with sensors and other peripherals, such as external sensors such as luminosity, temperature, air pressure, sound, geomagnetism, and acceleration.
[ad_2]
