Framework Design of Monitoring System for Traffic Based on Embedded and RFID Technology
Si Tian, Shuo Shi, Xuemai Gu
School of Electronics and Information Engineering Harbin Institute of Technology
Harbin, P. R. China, 150001
337tiansi@sina.com; crcss@hit.edu.cn; guxuemai@hit.edu.cn
Abstract—With the development of economics, an increasing number of people are involved in the road traffic. Therefore, the traffic security has been paid much more attention recently. The Traffic Monitoring Control System (MCS) can effectively supervise traffic participants so as to reduce the potential security risks. An Intelligent Traffic MCS scheme based on embedded Web server by applying several kinds of technologies like camera and Radio-frequency Identification (RFID) in the Vehicular Ad-Hoc Network (VANET) is designed and implemented in this paper. This system combines image surveillance system with vehicle identification information monitoring, which provides new ideas and methods for the real road monitoring.
Keywords—Intelligent traffic; monitoring system; embedded Linux; Radio-frequency Identification.
I. INTRODUCTION
In the 21st century, with the increasing development of the social economy, the number of vehicles per capita has also continued to increase in recent years. Although vehicles make people feel comfortable and make it more convenient to go out, they cause a lot of problems such as traffic congestion, emissions, traffic accidents, etc. Tens of hundreds of traffic participants, including a large number of private cars, buses, taxis, shuttle buses, pedestrians and cyclists, whose traffic behaviors are more casual and various in direction and speed, are in the large load net, which leads to the rapid change of traffic. On the road, we often meet with the traffic jam caused by traffic accident or other forms of accident. In order to distinguish the responsible party, to make the traffic lights smart, to infuse people’s observation and thinking into the fixed traffic management mode, as well as to make quick response to the traffic incidents, the intelligent transportation monitoring system comes into being.
Meanwhile, some behaviors that violate the Road Traffic Safety Law bring a lot of potential harm to other traffic participants. Intelligent traffic monitoring system can play a great role in obtaining evidence and supervising vehicles so that the police can manage the vehicle more effectively. When your car was stolen or left behind accidentally, the monitoring system that can locate the vehicle can provide effective information for police and the owner to search for the lost car.
Therefore, the traffic monitoring system combination of image
monitoring and vehicle identification information is significant to traffic management.
Usually, a video monitoring system is composed of front end cameras (camera, lens, encoder, PTZ, bracket, protective cover, etc.), transmission system (wired, wireless), monitoring center (matrix switcher, multimedia host), and terminal (monitor, VCR), as shown in Fig. 1. In the traffic monitoring system, an intersection usually has 1-2 cameras. The images taken by multiple camera front ends are transmitted through the network to the monitoring host. Then the monitoring host gathers the video sent by multiple cameras and then sends them to the terminal.
Front end camera 1
Front end camera 2
Front end camera n
Network transmission
Monitoring
host Terminal
Monitor
VCR
Video signal Control signal
Figure 1. Conventional monitoring system architecture
The monitoring system designed in this paper combines the two aspects of vehicle images and vehicle identification information, which has the advantages of small volume, low cost, and easy-to-batch production. The wireless transmission of camera picture data lays a very good foundation of the multi position and multi angle monitoring function. The application of embedded roadside gateway made the distributed monitoring system come true, and increased the stability of the system; the application of active RFID increased the intelligence of the monitoring system, and realized the quick identification and trace of vehicles [1].
The rest of this paper is organized as follows. Section II introduces the architecture of the system and the workflow.
Section III discusses the detailed design method of the system from three aspects of gateway, camera and RFID identification.
The hardware constitution and software design are also introduced in this section. By the experiment in section IV, the system designed in this paper is verified to be both feasible and efficient. Section V concludes this paper.
II. SYSTEM ARCHITECTURE AND WORKFLOW
In view of the fact that the malfunction in the center of the star-topology monitoring system is easy to cause the paralysis of the whole system, the intelligent traffic monitoring system is designed in the distributed architecture in this paper. The system architecture is shown in Fig. 2. The monitoring unit is peer unit in the distributed architecture. Each monitoring unit is a complete system, while the monitoring center plays the part of a centralized client in the distributed system. In this way, there will not exist monitoring blind time which is caused by monitoring unit or monitoring center malfunction, and the framework will release the pressure of central server. We define the network equipment in the monitoring unit as roadside gateway. The network composed of wireless monitoring equipment is called highway network; the Internet and user equipment which is connected to the roadside gateway is defined as external network.
Based on modular ideology, with the application of RFID, the monitoring unit designed in this paper can be divided into three subsystems in terms of hardware [2]. This top-down design not only reduces the complexity of system, improves the facility to expanding and upgrading, but also avoids the disastrous consequence of the system caused by single module
fault. Furthermore, the system design also takes the economy, extensibility and reusability of the system into account.
In this paper, camera and monitoring unit using RFID at one crossing or accident black spots is shown in Fig. 3. The camera is equipped on roadside which is used to monitor the real-time traffic; RFID tags are implanted in the vehicle by relevant departments, which are used to recognize vehicle ID fast. RFID reader is also equipped on roadside which is used to read the information of RFID tags. Camera communicating by Wi-Fi, RFID device and roadside gateway form the highway network of monitoring unit, which is used to gather and upload data. User terminal such as Web page and network equipment forms external network of system, which is used to provide remote monitoring interface for users conveniently.
The main development of the system focus on highway network. Camera communicates and delivers monitoring image data by WIFI protocol and roadside gateway. RFID reader connects to the roadside gateway by UART-USB. Active RF tags are set in vehicles, transmitting information to RFID reader using 2.4GHz band. Roadside gateway publishes the road information after collecting it. PC terminal and mobile phone can monitor road information through connecting to the Internet.
External Network
Highway Network2
Mobile Phone PC
Wi-Fi Ethernet
WIFI
RFID2 RFID1 Camera
Roadside Gateway
Wi-Fi
RFID2 RFID1 Camera
Roadside Gateway WIFI
RFID2 RFID1 Camera
Roadside Gateway
Highway Network3 Highway Network1
Ethernet
Ehernet
Ethernet Internet
Figure 2. Scenario of distributed system
Mobile Phone PC
Ethernet
Wi-Fi
Ethernet
External Network Highway Network
USB2.0 UART Wi-Fi
RFID Reader
RFID1
RFID3 RFID2
Roadside Gateway
2.4GHzRF Camera
Internet
Figure 3. Architecture of intelligent traffic monitoring unit
The framework designed in this paper is a kind of architecture that the center is roadside gateway, surrounded by multi camera multi RFID. The framework is shown in Fig. 4.
On the one hand, multi miniature low-cost cameras equipped in multi position and multi angle reduce the cost and expand the coverage of monitoring. On the other hand, Monitoring system based on RFID technology designed in this paper can identify the vehicle more quickly and accurately, and can roughly find the real-time location of vehicles by searching the vehicle information through the entire monitoring network.
Wi-Fi
Highway Network
RFID2 RFID1 Camera
Roadside Gateway
RFID4 RFID3
Camera Wi-Fi
Figure 4. Roadside gateway surrounded by multi camera multi RFID
The workflow is as follows: When a vehicle passes through the monitoring unit, vehicle RFID tag sends the vehicle identification information to the roadside gateway. At the same time, Wi-Fi cameras take pictures from multi position and multi angle and then store them. A server is embedded in the roadside gateway, which is used to publish the vehicle identification and picture information in the form of web page.
The users located in the monitoring center will monitor the traffic by access to the server.
III. SYSTEM DESIGN
A. Roadside Gateway Designed by Embedded System Roadside gateway is installed on the side of the road. It serves as publishing the website, gathering and storing the monitoring information, and sending it to the Internet, as well as interacting with the client.
The kernel of the roadside gateway is S3C6410 which is a kind of ARM11 chip made by Samsung. NAND FLASH is used to store fixed programs; SDRAM is employed to read and write the data when the system is running; USB interface is attached to the roadside gateway and the RFID reader; RJ45 Ethernet interface is attached to the roadside gateway and the Internet. The structure of roadside gateway equipment is shown in Fig. 5.
ARM11 Chip
S3C6410 USB2.0
RFID Reader DM9000
RJ45 Ethernet
Power Clock Reset
FLASH SDRAM
Figure 5. Structure of roadside gateway equipment
The roadside gateway equipment is programmed into the embedded Linux system which is highly customizable.
Programmers can add or delete the program according to the need of project [3]. What the programmers also need to do extra is recompiling the kernel and generating a new Linux file zImage
B/S network architecture, used as the network model of roadside gateway, has many advantages. For example, it can simplify client, shorten the development cycle, maintain and upgrade easily, possessing unparalleled advantages in functional development that the C/S architecture cannot match.
In the B/S architecture, the browser, server and database are three indispensable parts.
Fig. 6 shows the technology involved in the B/S architecture and the process of the data, which means that the users communicate with the remote server via webpage and call the Ajax program. And the server reacts by calling the local CGI (Common Gateway Interface) program.
Browser User Interface
Ajax Engine
Embedded Web Server Embedded Linux OS
Server Data Calling JavaScript
HTTP Request HTTP Response HTTP Transport
Figure 6. B/S network architecture
In order to support the access of users on the Internet, a web server needs embedding in the roadside gateway. Apache is the most widely used sever with outstanding performance, while the Boa server can only accomplish some simple tasks.
With less accessing users, the monitoring system designed in this paper does not require much better server performance, especially response speed and the concurrent characteristic.
And because of the special condition of embedded application scenario, the large server is not suitable in the roadside gateway.
Based on the above discussions, we select the Boa server which is only 70KB after cross compiling.
A database needs embedding in the roadside gateway so as to record the identification information of the vehicle near the roadside gateway. The lightweight database SQLite which can be transplanted easily among many database softwares is chosen. It requires less memory at run time and streamlines the code [4]. So the SQLite is faster and more effective on embedded devices.
B. Monitoring Vehicle by Camera
Camera module will realize the functions of visual real- time monitoring and wireless transmission. In order to complete the above functions, the scheme of camera module is as follows:
1) Use the miniature camera module which can convert the digital image data to TTL level.
2) Use the UART-WIFI module to convert the TTL level to Wi-Fi packet.
3) Receive the image data and control the camera by socket in the Wi-Fi receiver.
Because of the application of UART, the transmission speed is low. But it is at low cost which is very crucial in the multi camera architecture, and it can complete the function of
wireless transmission designed in this paper. The pseudo codes of operation of camera module are shown in Fig. 7.
a) Judge whether the complete parameter has been input. If not, program over.
b) Setup a socket connection.
c) Judge whether the connection is successful. If not, program over.
1) Set the picture size.
2) Empty the camera cache.
3) Set the camera compression ratio.
4) Reset camera.
d) Take pictures.
1) Send start command.
2) Read the picture size.
3) Read the picture data.
4) Write to binary file.
5) Stop taking pictures and empty the cache.
e) Judge whether or not to stop the program. If not, go to take pictures.
f) Program over.
Figure 7. Operation of camera module
C. Identifying Vehicle by RFID
Due to the large delay when communicating by Wi-Fi equipment and the Wi-Fi’s inability to support high-speed mobile carrier communication, the current vehicle road communication scheme mainly concentrated on the field of RFID technology. The RFID equipment falls into two categories: passive RFID (also called passive tags with no built-in battery) and active RFID. When the label is beyond the range of the RFID reader communication, electronic label is in the passive state; when the label is in the RFID reader communication range, electronic tags get its working energy from the RF energy that is sent by the RFID reader. Passive RFID uses reflection modulation mode to transmit information from electronic tags to the RFID reader in general. Typical applications of passive RFID are RF card system, supermarket exit anti-theft system etc. Active RFID has an internal power supply to supply the IC power to generate external signal [5].
Active tags have longer wireless communication distance and can support large memory capacity to store some additional information sent by the RFID reader. Typical applications are ETC system, parking fees system etc. Passive characteristics of passive RFID limits its effective communication distance, ranging from a few centimeters to several meters, while the active RFID can reach tens of meters to hundreds of meters.
The system designed in this paper uses active RFID instead of passive RFID because of the characteristic of vehicle-road communication in the traffic monitoring system. The nRF24LE1 chip is employed to make up the wireless transceivers. The nRF24LE1 is cost-effective and is embedded microcontroller 2.4GHz RF transceiver. The RF transceiver chip nRF24LE1 has several salient features as follows:
1) 8 bit micro controller with high speed; compatible with the Intel MCS51 instruction set; the instruction cycle is reduced; the performance is 12 times than that of traditional 8051 MCU, and it can be programmed by using the common MCU development software Keil.
2) 16KB on-chip program memory, 1KB on-chip data memory, 512 bytes non-volatile data memory.
3) Flexible input and output.
4) Power-saving mode, low power consumption, efficient running after awakening.
5) Support hardware debugging, which is convenient to modify the protocol for programmer.
The frame structure of the RFID is shown in Table 1.
TagID is the tag number; RSSI is the tag signal strength;
ReaderID is the RFID reader number; the others are fixed.
TABLE I. THE FRAME STRUCTURE OF ACTIVE RFID
Frame 7 6 5 4 3 2 1 0
Master
reader FB 10 00 00 TagID RSSI ReaderID 01 Slave
reader
FB 10 00 00 TagID RSSI ReaderID 02
RFID reader connects the roadside gateway by the UART.
Set the name of UART ttyUSB0; the Baud rate is 9600; 8 bits data, no check bit and 1 stop bit. The pseudo codes of operation of RFID module are shown in Fig. 8.
a) Initialize the UART.
b) Receive 8 bits data from RFID reader.
c) Frame check. If there is something wrong when checking the receiving frame, go to step b).
d) Store right frame.
e) Add a datum to the SQLite database.
f) Judge whether or not to stop. If not, go to step b).
g) The end.
Figure 8. Pseudo codes of operation of RFID module
IV. EXPERIMENT RESULT
The function and performance of the monitoring system was tested in this paper. Two cars mounted with RFID tags drove through a crossing where there is equipped with the monitoring system designed in this paper. The monitoring unit in the highway network took pictures, gathered and uploaded the vehicle identification information. At last, the roadside gateway published the webpage of monitoring. The vehicle identification information monitoring webpage is shown in Fig.
9. The traffic monitoring center can view all roads vehicles by accessing the Webpage, and can view all the crossings the vehicle past and its time by searching the vehicle identification in the Webpage. As can be seen in the Fig. 9, the marks of two cars were 1 and 2 respectively, and the two cars passed the crossing where the No.8 monitoring unit is located at a given time. From the upper-right corner of the page, the searching results can be seen. The performance was tested in this paper: a car carrying an RFID tag drove passing an intersection which is equipped with 3 wireless cameras at various speeds. And the number of pictures taken and the vehicle identification records were analyzed in statistics, as shown in Fig. 10 and Fig. 11. As can be seen from the graph, the number of records and the images decreases gradually as the speed increases. And the monitoring performance is still fantastic when the cars pass through the intersection at a speed of 120km/h. It also can be seen that the conventional intersection monitoring system performs worse. The conventional system can monitor 100%
vehicles with a speed of below 40km/h, while the performance gets worse when the speed is more than 40km/h. In consideration of the limits of the testing car performance, test site, and safety, the system was not tested when the vehicle speed was more than 120km/h.
Figure 9. Webpage of vehicle identification information designed
V. CONCLUSION
By using the technology of camera and RFID, a real-time intelligent traffic monitoring system, with the functions of real- time picture-taking and quick-identification of vehicle information, is proposed in this paper. The application of embedded roadside gateway made the distributed monitoring
system come true, and increased the stability of the system; the application of active RFID increased the intelligence of the monitoring system, and realized the quick identification and trace of vehicles. According to the above discussions, we can see that the intelligent traffic monitoring system put forward in this paper gave a stable and comprehensive traffic monitoring scheme, and proposed a new method of real traffic monitoring.
The research on the intelligent traffic monitoring system is of great significance to ensure the security of traffic.
20 40 60 80 100 120
0 5 10 15 20 25 30 35 40 45 50
Vehicle Speed(km/h)
Number of Pictures
New method Conventional method
Figure 10. Picture capture performance of the system
20 40 60 80 100 120
0 5 10 15 20 25 30 35 40 45 50
Vehicle Speed(km/h)
Number of RFID Records
Figure 11. Identification information capture performance of the system
VI. ACKNOWLEDGMENT
This work was sponsored by the National Natural Science Foundation Project of China (61101123).
VII. REFERENCES
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[2] Yu, Miao, et al. "Application of RFID and GPS Technology in Transportation Vehicles Monitoring System for Dangerous Goods."
Remote Sensing, Environment and Transportation Engineering, International Conference on. IEEE, 2012:1 - 4.
[3] Wen-hui, DAI. "Research of Remote Network Monitoring System Based on Embedded Linux." Computer and Information Technology (2012).
[4] Xiao, Xinyuan, et al. "Research on safety monitoring and evaluation system of dangerous goods transportation." Transportation, Mechanical, and Electrical Engineering (TMEE), 2011 International Conference on.
IEEE, 2011:1900 - 1904.
[5] Hongjian, Wang, et al. "RFID Technology Applied in Highway Traffic Management." Optoelectronics and Image Processing (ICOIP), 2010 International Conference on. IEEE, 2010:348 - 351.
