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Radio frequency identification (RFID), also known as electronic tag (E-Tag), is a technology that uses radio frequency signals to automatically identify target objects and obtain related information. The earliest applications of RFID can be traced back to the “identification of enemy and myself†system used to distinguish the coalition and Nazi aircraft during the Second World War [1]. With the advancement of technology, the field of RFID applications has been expanding. It has now involved all aspects of people's daily life and will become a basic technology for the future construction of the information society. RFID typical applications include: in the field of logistics for warehouse management, production line automation, daily necessities sales; in the field of transportation for container and parcel management, highway tolls and parking fees; in agriculture, animal husbandry and fishery for sheep, fish, fruit Such as management and pets, wildlife tracking; in the medical industry for drug production, patient care, medical waste tracking; in the manufacturing for the visual management of parts and inventory [2,3]; RFID can also be applied to books and Document management, access control management [3], location and object tracking, context awareness [4,5] and check security [6] and many other applications.
In March 2003, Gartner predicted on the "Symposium ITXPo 2003" that RFID (E-Tags) technology is a technology that will gradually begin to be used on a large scale in the last 2 to 5 years (2005 to 2008), as shown in Figure 1. According to ARC Consulting Group's forecast, the market demand for RFID in the global supply chain will reach 4 billion U.S. dollars by 2008, as shown in Figure 2. 
Figure 1 Trend Prediction of RFID Technology (Data Source: Gartner, March 2003) 
Figure 2 Global Market Analysis and Forecast of RFID Systems (Source: ARC Advisory Group, July 2004)
In the field of labels, bar code technology has been very mature and widely used, and almost all products are now bar coded. Due to the limited storage space, barcodes usually only identify the product type. Compared with barcodes, RFID tags have many advantages such as fast reading speed, large storage space, long working distance, strong penetrability, various shapes, strong adaptability to work environment, and reusability. Fast reading speed: It can complete the reading of hundreds of items of identification information in an instant, thereby improving work efficiency; Large storage space: It can achieve the whole process of single item management and tracking, overcome the barcode can only be on a certain Limits on the management of articles; long working distance: can achieve long-distance management of articles; strong penetrability: it can obtain information from paper, wood, plastic and metal packaging materials; labels can be used according to different applications Made into strips, cards, rings and buttons and other shapes. However, the cost of RFID tags is currently higher than the cost of a few cents or even a few cents.
The second section of this article will introduce the basic structure of the RFID system; Section III analyzes the current research status of RFID; Finally, it summarizes the full text and looks forward to the application prospect of RFID.
2 RFID System Overview
The basic RFID system consists of RFID tags, RFID readers, and application support software. Figure 3 shows a basic RFID system showing three different forms of RFID tags. 
Figure 3 Basic RFID system configuration
RFID tags are divided into two types: Active and Passive, depending on the way they send RF signals. Active tags send RF signals to readers, which are usually powered by a built-in battery, also known as active tags. Passive tags have no batteries, also known as passive tags. The energy required to launch the radio waves and the internal processor is Electromagnetic waves from the reader. After receiving the electromagnetic wave signal from the reader, the passive tag converts part of the electromagnetic energy into energy for its own work. Table 1 compares the active and passive tag characteristics. The active tag usually has a farther communication distance, and its price is relatively high. It is mainly used in applications such as remote detection of valuables. Passive tags have the advantage of being cheap, but their working distance, storage capacity, etc. are limited by the energy source. 
The main task of the RFID reader is to control the radio frequency module to transmit the read signal to the tag and receive the response of the tag, decode the object identification information of the tag, and transmit the relevant information of the object identification information associated with the tag to the host for supply. deal with. Depending on the application, the reader can be handheld or stationary. Current readers have high costs, prices are around $1,000, and most of them can only work at a single frequency. The price of future readers will be greatly reduced, and support for multiple frequency points, can automatically identify the tag information of different frequencies.
RFID Application Support Software In addition to software running on tags and readers, middleware between readers and enterprise applications is an important part of this. The middleware provides a series of computing functions for enterprise applications and is known as Savant in the Electronic Product Code (EPC) specification. Its main task is to filter, aggregate, and calculate the tag data read by the reader and reduce the amount of data transmitted from the reader to the enterprise application. Savant also provides interoperability with other RFID support systems. Savant defines two interfaces for readers and applications.
The user can select an RFID system suitable for his application based on working distance, working frequency, working environment requirements, antenna polarity, life cycle, size and shape, anti-interference ability, security and price and other factors.
3 RFID research status analysis
The current RFID research mainly focuses on RFID technology standards, RFID tag costs, RFID technology, and RFID application systems.
3.1 RFID technical standards
As a technology that will deeply affect everyone's daily life, in order to achieve unified management of items worldwide, but also to regulate the development of tags and readers, to solve the interconnection and compatibility problems of RFID systems, RFID must be Technology is standardized. The standardization of RFID is an important issue that needs to be solved urgently. Countries and relevant international organizations are actively promoting the development of RFID technology standards. At present, there are not yet complete international and domestic standards for RFID. The standardization of RFID involves identification of coding standards, operating protocols, and application system interface specifications. The identification coding specification includes the identification length, coding method, and the like; the operation agreement includes specifications such as air interface, command collection, and operation flow. At present, the main RFID-related specifications are the European and American EPC specifications, the Japanese UID (Ubiquitous ID) specification, and the ISO 18000 series of standards. The ISO standard mainly defines the air interface between the tag and the reader for interoperation.
The EPC specification was developed by the Auto-ID Center and later established EPCglobal [7]. The Auto-ID Center was established in 1999 by the Massachusetts Institute of Technology (MIT). Its goal is to create a global "internet of things" network that has received extensive support from the U.S. government and business community. On October 26th, 2003, a new EPCglobal organization was established to replace the previous Auto-ID center and manage and develop the EPC specification. Regarding labels, the EPC specification has promulgated the first generation of specifications. The specification subdivides the labels into Class 0, Class 1, and Class 2 types. Class 0 and Class 1 tags are written once and read multiple tags, Class 0 tags can only be written by the manufacturer, the user can not be modified, it is also known as read-only tags, mainly used for supply chain management; Class 1 It provides more flexibility, information can be written once by the user. Class 0 and Class 1 tags use different air interface standards for communication, so the two types of tags cannot interoperate. The Class 2 tag has multiple write capabilities and adds some storage space for storing user's additional data. The Class 2 tag allows the addition of security and access control, sensing networks, and Ad hoc networks. EPCglobal is currently developing a second-generation labeling standard, UHF Class 1 Generation 2 (C1G2). C1G2 has the ability to update the content of tags at any time, ensuring that tags always keep the latest information. The EPC specification version 1.0 currently includes the EPC Tag data specification, Class 0 (900 MHz) tag specification, Class 1 (13.56 MHz) tag interface specification, Class 1 (860 MHz to 930 MHz) tag radio and logic communication interface specification, and Physical Markup Language (Physical Markup) Language, PML).
The UID (Ubiquitous ID) specification is developed by the Ubiquitous ID Center in Japan [8]. The Ubiquitous ID Center in Japan was established by the T-Engine Forum. Its goal is to establish and promote automatic item identification technology and eventually build a ubiquitous computing environment. The specification does not impose requirements on the frequency band. The tags and readers are multi-band devices that can support the 13.56 MHz or 2.45 GHz frequency band simultaneously. The UID tag refers to all devices that contain ucode codes, such as barcodes, RFID tags, smart cards, and active chips, and defines nine different types of tags. Associated with RFID tags include: Class 1 read-only RFID tags, Class 2 read-write RFID tags, Class 5 powered RFID tags. In addition to the labels, the UID network also contains two other key parts: The first is the terminal that reads the labels, called ubiquitous communicators (UCs). In addition to communicating with labels, it also provides 3G, PHS, 802.11, etc. Multiple access methods are connected to the information server on the WAN; the other is the ucode resolution server, which provides the function of obtaining the address of the information server from ucode.
There are currently three versions of EPC encoding, the main difference being the different encoding lengths, 64, 96, and 256 bits, respectively [11]. The purpose of using 64-bit encoding is to reduce tag storage and thus reduce tag production costs; 96-bit encoding is to achieve a balance between performance and cost; but in order to meet the goal of providing identification for any object in the world, it must use at least 256 Bit encoding. The three versions of the EPC code are composed of four common domains, which are: version number, management domain (corresponding manufacturer), category (product type), serial number (identification of single item).
The UID code length is 128 bits, and can be expanded to 256, 384, or 512 bits as needed. UID encoding consists of three fields, which in turn are: coding category identifiers, used to be compatible with existing coding standards, such as EAN, UPC, ISBN, etc.; encoding content of a coding standard, used to identify a certain type of goods; unique identification, The specific individual used to identify a product.
Figure 4 compares the EPC and UID coding conventions. 
Figure 4 EPC and UID coding specifications
Currently, RFID technology research focuses on the selection of operating frequencies, antenna design, anti-collision technology, and security and privacy protection.
3.2.1 Selecting Operating Frequency
Operating frequency selection is a key issue in RFID technology. The choice of operating frequency must be adapted to the requirements of different applications. It is also necessary to consider the regulations for the use of radio frequency bands and transmit power in various countries. At present, the RFID operating frequency spans multiple frequency bands. Different frequency bands have their own advantages and disadvantages. It affects not only the performance and size of the tag, but also the price of tags and readers. In addition, the difference in radio transmission power affects the reader-writer operating distance.
The low-frequency band energy is relatively low, the data transmission rate is small, and the wireless coverage is limited. To increase wireless coverage, the tag antenna size must be increased. Although low-frequency wireless coverage is smaller than high-frequency wireless coverage, the antenna has poor directionality and relatively strong ability to bypass obstacles. The low frequency band can use 1 to 2 antennas to achieve full coverage of the wireless range. In addition, the low-band electronic tag has a relatively low cost and has various shapes such as a card shape, a ring shape, and a button shape.
The high-frequency band energy is relatively high and is suitable for long-distance applications. The low-frequency power loss is proportional to the cube of the propagation distance, and the high-frequency power loss is proportional to the square of the propagation distance. Because the high frequency propagates as a beam, it can be used for smart tag positioning. The disadvantage is that it is easily blocked by obstacles, and is easily affected by factors such as reflection and human disturbance, and it is not easy to achieve full coverage of the wireless coverage area. The high frequency band data transmission rate is relatively high, and the communication quality is better. Table 2 shows the RFID frequency band characteristics table. 
An antenna is a device that receives or radiates radio signal power from a radio transceiver in the form of electromagnetic waves. Antennas can be classified into short-wave antennas, ultra-short-wave antennas, and microwave antennas according to their operating frequency bands. Directional antennas can be classified into omnidirectional antennas and directional antennas. According to their shape, they can be classified into linear antennas and planar antennas.
Due to limitations of the application, RFID tags usually need to be attached to the surface of different types and shapes of objects, and even need to be embedded inside the object. RFID tags require high reliability while requiring low cost. In addition, the tag antenna and the reader-writer antenna also assume the role of receiving energy and transmitting energy, respectively. These factors put forward strict requirements for the design of the antenna. The current research on RFID antennas focuses on the effects of antenna structure and environmental factors on antenna performance.
The antenna structure determines the characteristics of the antenna pattern, polarization direction, impedance characteristics, VSWR, antenna gain, and operating frequency band. Directional antennas are suitable for electronic tag applications because they have less return loss. Because the orientation of RFID tags is not controllable, the reader antenna must adopt circular polarization (the antenna gain is large); the antenna gain and impedance characteristics will The effect distance of the RFID system has a greater impact; the working frequency band of the antenna has a great influence on the antenna size and the radiation loss.
Antenna characteristics are affected by the shape and physical characteristics of the identified object. For example, if a metal object attenuates the electromagnetic signal, the metal surface will reflect the signal, the elastic base layer will cause the label and the antenna to be deformed, and the size of the object has certain restrictions on the size of the antenna. Various solutions have been proposed based on the above characteristics of the antenna, such as using a meandering antenna to solve the size limitation [11], and using an inverted F antenna to solve the reflection problem on the metal surface [12].
The antenna characteristics are also affected by the objects and environment around the antenna. Obstacles can hinder the transmission of electromagnetic waves; Electromagnetic shielding of metal objects can result in inability to read the content of the electronic tags correctly; other broadband signal sources, such as engines, pumps, generators, and AC/DC converters, can also generate electromagnetic interference. , affect the correct reading of electronic tags. How to reduce electromagnetic shielding and electromagnetic interference is an important direction of RFID technology research.
3.2.3 Anti-collision Technology Research
In view of the fact that multiple electronic tags operate on the same frequency, when they are in the same scope of the reader/writer, without using a multiple access control mechanism, the information transmission process will produce a conflict, resulting in failure of information reading. At the same time, the overlap of working ranges between multiple readers will also cause conflicts. Document [13] proposed the Colorwave algorithm to solve the reader conflict problem. According to the different frequency bands of electronic tags, people have proposed different anti-collision algorithms.
For tag conflict, the anti-collision algorithm of the tag generally adopts the classical ALOHA protocol in the high frequency (HF) band. Use the ALOHA protocol tag to avoid conflicts by selecting a way to send information to the reader at random times. Most HF readers can scan dozens of electronic tags at the same time. In the UHF band, tree bifurcation algorithms are mainly used to avoid collisions. Compared with the high-frequency band electronic tag using the ALOHA protocol, the tree bifurcation algorithm has more leakage information and is less secure.
The above two tag anti-collision methods belong to Time Division Multiple Access (TDMA) mode and are widely used. In addition, there are currently proposals for frequency-division multiple access (FDMA) and code-division multiple access (CDMA) anti-collision algorithms, which are mainly used in UHF and microwave applications.
3.2.4 Security and Privacy Issues
RFID security issues focus on various aspects such as privacy protection for individual users, protection of commercial secrets for enterprise users, prevention of attacks on RFID systems, and security prevention using RFID technology. The challenges are:
· Ensure that the user’s possession of the information on the label is not being accessed without authorization to protect the user’s privacy in terms of consumption habits, personal whereabouts, etc.;
Avoiding RFID system reading speed, can quickly scan all the goods in the supermarket and track changes, and be used to steal user commercial secrets;
·Protection against various types of attacks on RFID systems, such as: rewriting tags to tamper with article information; using special equipment to counterfeit tags to counter fraudulent readers to create artifacts; and remote eavesdropping tags based on RFID asymmetry. Information; implementation of denial of service attacks by interfering with the working frequency of RFID; destruction of tags by the emission of specific electromagnetic waves;
How to use RFID's unique identification features for access control security, check security, and product security.
In order to prevent RFID tags from bringing customer concerns about personal privacy, and also to prevent confusion caused by users entering the market with tagged products, many merchants remove the tags when the goods are delivered to customers. This method undoubtedly increases the system cost, reduces the utilization of RFID tags, and in some cases the tags cannot be removed. In order to solve the above security and privacy issues, people also propose a variety of technical solutions, as shown in Table 3. 
Based on the unique identification characteristics of RFID tags on objects, it has triggered an upsurge of research on RFID-based applications. Logistics and physical Internet are the hotspots of current RFID application research. Other applied researches include space positioning and tracking, pervasive computing, and system security.
3.3.1 Logistics and Physical Internet
The physical Internet is to build an all-involved item information network on the basis of the existing Internet by attaching RFID tags to all items. The establishment of the physical Internet will affect all aspects of the circulation of goods such as manufacturing, sales, transportation, use, and recycling, and will have a profound impact on the behavior of governments, enterprises, and individuals. Through the physical Internet, any item in the world can be identified, tracked and monitored on demand, anywhere, anytime. The physical Internet is seen as another revolution in the IT industry following the Internet.
In order to realize the goal of the physical Internet, EPCglobal introduced several core technologies such as Savant, Object Name Service (ONS), and Physical Markup Language (PML)[7] based on the basic RFID system. In the physical Internet, when the product is completed, it is affixed with an RFID tag that stores the EPC logo. From then on throughout the product's life cycle, the EPC code becomes the product's unique identifier. This EPC code is indexed to be real-time on the EPC network. Inquiries and updates on product-related information can also use it as a clue to position and trace products in various circulation links. In any link such as transportation, sales, use, and recycling, when a reader detects the presence of a tag within its reading range, the EPC data contained in the tag is transmitted to the connected Savant, and Savant first uses the EPC data. For the key value, the local ONS server obtains the network address of the EPC information server containing the product information, and then Savant queries the EPC information server according to the address to obtain the specific information of the product, and performs necessary processing to trigger the back-end enterprise application to make deeper Hierarchical calculations, at the same time, the local EPC information server and the source EPC information server record and modify the corresponding data for this reader reading. If the local ONS cannot refer to the EPC information server address corresponding to the EPC encoding, it will send a resolution request to the remote ONS. The entire physical Internet architecture is shown in Figure 5. 
Figure 5 Physical Internet Architecture
3.3.2 Space Positioning and Tracking
The popularity of wireless and mobile communication devices has driven people's need for location-aware services. People need to determine the three-dimensional coordinates of items and track their changes. Existing location service systems mainly include GPS systems based on satellite positioning, positioning systems based on infrared or ultrasound, and positioning systems based on mobile networks. The popularity of RFID provides a new solution for space and tracking services for people and objects. The RFID positioning and tracking system mainly utilizes the unique identification characteristics of the tag to the object, and measures the spatial position of the article based on the signal strength of the radio frequency communication between the reader and the tag mounted on the object. The RFID positioning and tracking system is mainly used in indoor positioning where the GPS system is difficult to apply. .
Typical RFID location and tracking systems include the Cricket system developed by the MIT Oxygen project [14], the LANDMARC system of Michigan State University [15], and the Microsoft RADAR system [16]. In view of the low price of RFID tags, the introduction of reference tags and the use of RFID tags as reference points [15] can improve system positioning accuracy and reduce system costs.
3.3.3 Pervasive computing
RFID tags have unique identification capabilities for objects, and can be used in combination with sensor technology to sense the state information of surrounding objects and the environment such as temperature, humidity, and lighting [19], and to use wireless communication technology to conveniently make these status information and changes. Pass it to the computing unit, improve the visibility of the environment to the computing module, build the infrastructure for future pervasive computing, make computing everywhere, and provide services for people on an active, on-demand basis.
3.4 RFID tag costs
The cost of RFID tags is the key to the success of their commercial applications. The cost of an RFID tag is mainly composed of several parts such as an IC chip, an antenna, and a package. According to the survey of ARC Consulting Group, the average price of passive HF band tags was 91 cents in 2003, and the average price of UHF band tags was 57 cents[9]. With the advancement of integrated circuit technology and the expansion of the application scale, the cost of RFID tags will continue to decrease. According to the forecast of the Auto-ID Center, in the case of large-scale production, the lowest production cost of RFID tags can be reduced to 5 cents, including about 1 to 2 cents for IC chips and 1 cents for antennas[10]; ARC Consulting Group It is predicted that by 2008, the average price of passive HF band tags will drop to 30 cents, and the average price of UHF band tags will drop to 16 cents[9]. In addition, the cost of RFID readers is also one of the factors that affect RFID applications. Due to the huge technical advantages of RFID systems, this will result in a significant increase in work efficiency, thus reducing the total cost of ownership of the system.
The application and promotion of RFID systems also involves the transformation of existing business systems. Currently, a large number of companies adopt bar code, ERP, and data warehouse technologies to manage their own production and sales processes. How to reduce the cost of converting an existing business system into an RFID-based one is also an important issue in current RFID research.
4 Conclusion
RFID will build a bridge between the virtual world and the physical world. It can be foreseen that in the near future, RFID technology will not only be widely adopted in all walks of life. Ultimately, RFID technology will be integrated with pervasive computing technology and have a profound impact on human society.
As a global manufacturing base, China will be the world's largest RFID application market in the future. This will be a rare opportunity for domestic research institutions and enterprises. At present, China's research on RFID chips, RFID system security and other core technologies is almost blank, and RFID applications are still at the initial stage. We believe that in the environment of government promotion and corporate participation, attracted by the huge market space, more and more companies and research institutions will participate in the research and development and application of RFID technology in China, and more companies will use RFID. Technology for enterprise information transformation. China will not only dominate the application market for RFID technology, but also become the global R&D center for RFID technology.
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About the Author:
Li Jintao was born in Hunan in 1962. He graduated from the Institute of Computing Technology, Chinese Academy of Sciences in 1989 with a Ph.D. in engineering. From 1989 to 1990, he was engaged in guest research at the Artificial Intelligence International Laboratory of the Czech Academy of Sciences. He has successively undertaken research tasks for a number of national 863 program projects, national science and technology research projects, and natural science fund projects. The main research directions are pervasive computing, multimedia technology, and virtual reality technology. He is currently a research fellow at the Institute of Computing Technology, Chinese Academy of Sciences, a doctoral tutor, director of the Digital Technology Research Office, and deputy director of the Beijing Municipal Science and Technology Commission (technical deputy).
Radio Frequency Identification (RFID) Technology and Its Application
1 Introduction