1 Introduction to RFID
Radio frequency identification (RFID) is an automatic identification technology rising in the 1990s. This technology is a non-contact automatic identification technology. Its basic principle is to realize the automatic identification of the identified object by using the transmission characteristics of RF signal and spatial coupling (inductive or electromagnetic coupling). Its core technology includes radio frequency, computer software and hardware, coding, chip processing technology and other modern high-tech science and technology. It is a complex of a variety of cross category science and technology. It is widely used in many fields, such as industrial automation, commercial automation, modern service industry, transportation control management and so on.
1.2 system composition, working principle and working frequency of RFID
The composition of RFID system will be different due to different applications, but the basic RFID system is composed of electronic tag, reader and antenna. The functions of each part are as follows:
(1) Tag (radio frequency card): also known as contactless IC card, ID card, RF card, etc., it is composed of coupling elements and chips. The tag contains a built-in antenna for communication with the radio frequency antenna. Each tag has a unique electronic code (EPC) and is attached to the target object to be identified. It has the functions of intelligent reading and writing and encrypted communication. It exchanges data with reading and writing equipment through radio waves. The working energy is provided by the RF pulse sent by the reader.
(2) Reader: also known as reader / writer, readout device, etc., it is a device used to read (or write) label information. It can transmit the read-write command of the host to the electronic tag, encrypt the data sent from the host to the electronic tag, decrypt the data returned by the electronic tag and send it to the host.
(3) Antenna: transmit RF signal between tag and reader. Flat panel antenna, Yagi antenna and array antenna are mainly used in low frequency band and high frequency band.
In addition, a complete RFID application system also includes: Middleware (application interface), also known as RFID management software, which shields the diversity and complexity of RFID devices and can provide strong support for the background business system; Application hardware; Application software to record data and realize enterprise management functions.
The working principle of a typical RFID system is as follows: after the system is powered on, the reader periodically sends out an electromagnetic wave (excitation signal) of natural frequency through its internal coil. When the RFID card is placed within the induction range of the reader, the coil in the card generates a weak current under the induction of “excitation signal” as the power supply of the integrated chip in the card. After the card is powered on and reset, the card originally in the “sleep state” is activated, and the information code containing its own type identification code mark, manufacturer’s mark and other information codes are modulated to the carrier and transmitted through the antenna in the card. The card reading module transmits the received wireless signal to the field controller, which processes the signal and sends instructions to the execution device. The reader is controlled by microprocessor and realizes information exchange with the main control computer through wigan-485 conversion module. Its principle block diagram is shown in Figure 1.
The working frequency of NFID system mainly includes: low frequency, 125 kHz; High frequency, 3.56 MHz; VHF, 869 MHz, 902 ~ 928mhz; Microwave band, 2.45 GHz and 5.8 GHz, etc. The 125 kHz system is mainly used in the fields of animal identification and commodity circulation, and the high-frequency 13.56 MHz system is generally used in the fields of public transportation and access control system. In UHF frequency band (869 MHz, 902 ~ 928 MHz), the identification distance of the system is far, which can be applied to highway toll collection, container identification, identification and tracking of railway vehicles. Microwave 2.45 GHz, passive tags can generally provide a recognition distance of about 1 m, and active tags can also reach a recognition distance of more than 10 meters. The 5.8 GHz system is mainly used in the field of transportation. At present, this frequency band is also used as the system standard of vehicle identification in the interim standard of highway network toll collection system in China. Generally, the higher the working frequency, the farther the recognition distance and the stronger the directivity, but the worse the penetration ability.
1.3 advantages of RFID as a new generation identification technology and problems to be solved
1.3.1 advantages of RFID Technology
Compared with traditional bar code identification technology, RFID has the following advantages:
Fast scan for bar codes, only one bar code can be scanned at a time; RFID adopts a non-contact mode without directional requirements. As soon as the tag enters the magnetic field, the interpreter can read and write the information immediately. It usually completes reading and writing once in a few milliseconds. It adopts the anti-collision mechanism to process multiple tags at the same time, realize batch identification, identify up to 50 Tags / s at the same time, and identify in motion.
Small size and diversified shape RFID is not limited by size and shape in reading, and does not need to match the fixed size and printing quality of paper for reading accuracy. In addition, RFID tags can be miniaturized and diversified to apply to different products.
Anti pollution ability and durability the carrier of traditional barcode is paper, so it is easy to be polluted, but RFID has strong resistance to substances such as water, oil and chemicals. In addition, because the bar code is attached to the plastic bag or outer packaging carton, it is particularly vulnerable to damage; RFID volume label stores data in the chip, so it can be free from contamination.
It can be reused. Today’s bar codes cannot be changed after printing. RFID tags can repeatedly add, modify and delete the data stored in RFID labels to facilitate the update of information.
Penetrating and barrier free reading when covered, RFID can penetrate non-metallic or non transparent materials such as paper, wood and plastic, and can conduct penetrating communication. The bar code scanner must be close and there is no object blocking before it can read the bar code.
The memory capacity of data is large, the capacity of one-dimensional bar code is 50 B, the maximum capacity of two-dimensional bar code can store 2 ~ 3000 B, and the maximum capacity of RFID is more than 294. With the development of memory carrier, the data capacity also tends to expand. In the future, the amount of information that items need to carry will be larger and larger, and the demand for the expansion capacity of volume labels will increase accordingly.
Security RFID is solidified in the chip before leaving the factory according to the international unified coding system of electronic product code. It does not repeat the 40 bit unique identification code and cannot be copied and changed. Data can be encrypted, sectors can be locked independently, and important information can be locked according to users. This technology is difficult to be counterfeited and invaded, making domestic chips safer.
1.3.2 problems to be solved in RFID system
(1) Selection of RFID coding standard. At present, there is no unified standard about electronic tag (RFID) all over the world. In terms of China’s standard formulation, the National Standards Commission has jointly conducted research on China’s RFID standards with 14 units such as the Ministry of science and technology, the Ministry of information industry and Shanghai Institute of standardization. At present, the draft of RFID standards for animals has been completed, and Shanghai has launched the general technical specification for electronic labeling of animals, but the specification is only preliminary, It is still under continuous improvement, and it is still difficult to promote it nationwide in a short period of time. The RFID standard of other kinds of agricultural products other than animal husbandry remains to be studied.
(2) RFID information security. RFID data security is also an attractive topic. Because some data is saved in electronic tags, privacy protection has become a very important problem, and even a key point affecting the future of commercial applications. Because the reading of electronic tag data is triggered by the radio frequency transmitted by the reader, that is, as long as the transmission frequency of the reader is the same, the transponder, that is, the tag, will make the same response and transmit the same data, which will create an opportunity for criminals.
In order to solve the above problems, the reading of ID must be limited. At present, the most successful way is to use encryption. By embedding encryption in the electronic tag, the real-time monitoring data can be written into the database. If some system parameters work abnormally, warning information must be given in the interface and the monitoring system must be regulated. In order to facilitate users’ observation and intuitive understanding, it is necessary to convert the collected data into an intuitive and easily acceptable form for users to display, that is, the data is expressed in the form of charts. The GUI in VC can easily support the implementation in the form of chart.
2 Application of RFID technology in ETC system
2.1 etc system overview
In the development of automatic vehicle identification technology, many different automatic identification technologies have been tested and implemented, such as induction coil identification technology, surface acoustic wave identification technology, bar code identification technology, infrared communication identification technology and radio frequency identification technology. However, the mainstream comes down to the automatic vehicle identification technology using radio frequency identification technology as etc system.
ETC system, commonly known as non-stop toll collection system, is an intelligent transportation electronic system dominated by modern communication technology, electronic technology, automatic control technology, computer and network technology to realize non-stop automatic toll collection. Through the special short-range communication between the roadside antenna and the on-board electronic tag, the system carries out the automatic vehicle identification and the exchange of relevant charging data, processes the charging data through the computer network, and realizes the full electronic charging management system of automatic charging without stopping.
The radio frequency identification system uses the radio frequency card (radio transceiver) installed in the vehicle to store the vehicle number and relevant information. The radio frequency antenna installed in the lane can exchange information with the radio transceiver in the form of dedicated short-range communication (DSRC), and read and write the stored content, so as to identify the current passing vehicle.
The non-stop charging system has three main characteristics: non-stop, unmanned operation and cashless transaction. ETC technology has a long history of development abroad. Electronic toll collection systems in many countries and regions such as the United States and Europe have been locally networked and formed economies of scale. At present, Kanto expressway has fully realized etc charging, and only some lanes are reserved for mixed etc and semi-automatic charging. Most commercial vehicles have been equipped with etc on-board units, and many regions in China have begun to use etc system to upgrade expressway toll management system.
The non-stop toll collection technology is especially suitable for highway or bridge and tunnel environment with heavy traffic. The traditional Lane isolation charging system is called single lane non-stop charging system, and the non-stop charging system under free communication without Lane isolation is generally called free flow non-stop charging system. The implementation of non-stop toll collection technology can not only greatly improve the traffic capacity of the highway and make the highway toll automatic, but also greatly reduce the noise level and waste gas emission at the toll gate. Thus, it not only saves the capital construction cost and management cost, but also makes outstanding contributions to the improvement of urban environment. Electronic toll collection system represents the most advanced toll collection technology today, and it is also the direction of future development. It has broad development prospects.
2.2 working principle of non-stop toll collection system
2.2.1 technical principle of ETC system
ETC system collects RF card information from a long distance and non-contact to realize the automatic identification of vehicles in the fast-moving state, so as to realize the automatic management of targets. At present, the requirement of the system is that the remote card reader can read a distance of at least 10 meters. Due to different technical requirements and actual conditions, the models of card readers are also different. As for the working frequency range, the current electronic toll collection system is determined near 5.8 GHz, and the standards of most countries such as Europe, Japan, the United States and China are determined in the frequency band of 5.8 ~ 5.9 GHz.
The selection of 5.8 GHz band in China has the following advantages: firstly, the standard system of China’s communication system is close to the European standard system, and the allocation of radio frequency resources is roughly the same. Secondly, the background noise in 5.8 GHz band is small, and it is easier to solve the interference and anti-interference problems in this band than 915 MHz and 2.45 GHz. Thirdly, there are many equipment suppliers in the 5.8 GHz band, which is conducive to the equipment introduction of China’s etc system, reduce the system cost, and carry out other services in the field of intelligent transportation system in the future.
2.2.2 system composition of ETC system
ETC system is mainly composed of etc toll lane, toll station management system, etc management center, professional bank and transmission network. Lane control subsystem is used to control and manage the communication between various outfield equipment and electronic labels installed on vehicles, record various vehicle information and transmit it to toll station management subsystem in real time. The toll station management subsystem is responsible for collecting and managing the data transmitted. Etc management center is the top management of ETC system. It not only processes and exchanges toll information and data, but also performs necessary management functions. It includes toll franchised companies, settlement centers and customer service centers of all roads, and carries out transactions, account splitting and financial settlement between toll franchised companies and users according to the received data files, Equipped with multiple powerful computers to complete the acquisition and processing of various data and images in the system. Figure 2 is its structural block diagram.
2.2.3 work flow of ETC system
The owner shall purchase the on-board electronic label at the customer service center or agency and pay the stored value. The issuing system inputs the vehicle identification code (ID) and password to the electronic tag, and stores all relevant information of the vehicle in the database (such as identification code, license plate number, model, color, stored value, owner’s name, telephone, etc.). The distribution system inputs the owner and vehicle information into the charging computer system through the communication network. The owner can stick the identification card on the front window glass in the car. When the vehicle enters the etc toll lane and is in the transmitting area of Li antenna, the dormant electronic tag wakes up and starts working under microwave excitation; The electronic tag sends the electronic tag and model code by microwave; After the antenna receives and confirms that the electronic tag is valid, it sends the Li Lane code and time signal by microwave and writes them into the memory of the electronic tag. When the vehicle drives into the transmission range of the antenna at the exit of the toll lane, after the process of wake-up and mutual authentication effectiveness, the antenna reads the vehicle model code and the entry Li code and time, and transmits them to the lane controller. The lane controller stores the original data and edits it into a data file, which is uploaded to the toll collection station management subsystem and transferred to the toll settlement center.
If the vehicle has invalid identification or no card. When passing through the toll lane at high speed, while confirming the invalidity, the antenna will start the fast automatic railing, close the toll lane, and intercept the vehicles flushing the card on the spot; When there is no special toll lane for free flow toll collection, the fee evasion capture camera can be started to record the head and license plate number of the fee evasion and card flushing vehicle, and send it to the lane controller together with the Li code and card flushing time for recording, and then deal with it according to law.
After receiving the collected charging information of each company, the charging settlement center and the management bank deduct the toll and calculated amount from each user account and transfer it to the corresponding company account. At the same time, the bank shall check whether the remaining amount of each user account is lower than the predetermined critical threshold. If it is lower than the threshold, the bank shall timely notify the user to make up the amount and continue to pass. If the remaining amount is lower than the dangerous threshold, the bank shall classify it as an invalid electronic tag, make a blacklist, and notify each toll station to refuse the passage of the invalid electronic tag in the expressway electronic toll lane.
The charge settlement center has a user service organization, which sells identification cards to users, collects supplementary amounts and receives customer inquiries. The backstage has a set of financial operation rules and strong computer network and database support to deal with post charge and other matters.
3 development prospect of RFID
At present, RFID technology has been applied in many industries in China and achieved good results. For example, China has launched RFID application pilot work in qualified departments and places, mainly in the fields of industrial automation; Business automation; Automobile industry; Production management; Supply chain management and modern logistics. RFID technology has become the main development direction of global automatic identification technology in the 21st century. In particular, the application of RFID technology in ETC system has made an indelible contribution to the development of traffic charging industry. From the perspective of the future development of transportation network, etc system will become the mainstream of transportation industry, so the system has broad development prospects in the transportation toll industry.
Through the application of RFID technology in various industries and gradually occupying the mainstream position, it can be seen that RFID technology has stood out from many identification technologies and has been continuously developed and improved. Compared with the traditional charging system, etc system based on RFID technology has absolute development advantages, and the implementation of the system is relatively simple. With the development of RFID technology, etc system will be gradually improved.