Wireless RF Identification Technology (RFID)
RFID is an abbreviation in English "Radio Frequency Identification". RF technology is to read and write the recording medium using radio waves. The distance from RF recognition can reach tens of centimeters to a few meters, and according to the way of reading and writing, the information of thousands of bytes can be entered, while also highly confidentiality. Fields applicable to RFIT: Material tracking, vehicle and carriage recognition require non-contact data collection and exchange, requires frequently variable data content to change data content. Such as Hong Kong's vehicle automatic recognition system - driving, the main technique adopted is RF technology. At present, there are about 80,000 vehicles in Hong Kong to install electronic labels, and the electronic label is installed with electronic labeling, and there is no need to park the speed, improve the parking, and improve the parking fee. Efficiency. RF technology has also been widely used in identification and automation management of other items. Now, RFID is the most popular technology in the AIDC field. Although this technique has developed for many years, it is only available to a technical standard in the future. ISO and AIM (Auto-ID Manufactures) are working in this area, believe in the near future, RFID will develop very quickly. 1. The composition of the RFID system RFID system In a specific application process, according to different application purposes and application environments, the composition of the system is different, but from the RFID system's working principle, the system is generally by the signal transmitter, Signal receiver, part of the transmitting receiving antenna consists. The following description is described below:
1) In the RFID system, the signal transmitter will exist in different forms for different applications, and the typical form is the label (TAG). The tag is equivalent to the barcode symbol in the bar code technology, which is used to store information that needs to be identified. In addition, the barcode must be able to automatically or actively emit the stored information under the action of an external force. The label is typically a low electric integrated circuit with a coil, antenna, a memory and a control system. Typical label structure As shown in the figure: There are many different categories in different classification standards. (1), active label, passive tags in practical applications, must be powered by labels to work, although its electric energy consumption is very low (generally one millhwatt level). Different by label acquisition power, you can divide the tag into an active tag and a passive tag. The active label is self-taking the battery, its electrical energy is sufficient, high work reliability, and the distance from signal transmission is far. In addition, the active tag can limit the number of use times or the number of use of the label, which can be used in a location where the battery is used, which can be used in a place where the data transfer is required or the use of data is limited, and within one year, the label only allows read and write. Finite. The disadvantage of the active label is mainly limited by the label service life, and as the battery power consumption, the distance between data transmission is getting smaller and affects the normal operation of the system. The passive tag does not carry a battery internally, and it is necessary to provide energy from the outside world. The passive label typically generates electrical energy is an antenna and a coil. When the label enters the work area of the system, the antenna receives a particular electromagnetic wave, and the coil generates an induction current, and the label is powered by the rectifier circuit. The passive tag has a permanent usage, often used in the label information to read or read or frequently read and write multiple times a day, and the passive tag supports long-term data transfer and permanent data storage. The disadvantage of the passive tag is mainly to be smaller than the active tag. Because the passive label relies on the external electromagnetic sensing, its electrical energy is relatively weak, the distance and signal strength of data transmission are limited, and the signal receiver (reader) that is relatively high in sensitivity can be reliably read. (2) The read-only label and readable writable label can be divided into read-only tags and readable writable labels depending on the memory type internally. The only read-only label has only read only memory ROM (Rand ONLY MEMORY) and random memory RAM (Random Access Memory). The ROM is used to store the transmitter operating system description and security requirements, which complete the internal operation control function of the internal processor or logic processing unit, such as response delay time control, data stream control, power switch control, and the like. In addition, the ROM of the read-only label also stores identification information with the label. These information can be written in the ROM in the label manufacturing process, or write special encoding information based on a particular application purpose when the label begins using a particular application purpose. This information can only simply represent "0" or "1" in the binary, or it can contain complex quite abundant information like a two-dimensional bar code. But this information can only be written once, and read multiple times. The RAM in the read-only label is used to store the temporary data in the data transmission process. In addition, in addition to the ROM and ROM in addition to the ROM and ROM, in addition to the ROM and ROM, it is generally stored for temporarily storeing information waiting for the antenna sent after modulation. The memory inside the readable writable label is in addition to the ROM, RAM, and the buffer memory, as well as an inactive programmable memory memory. In addition to storing data functions, this memory has functions that allow multiple write data in an appropriate condition.
There are many kinds of non-active programmable memory memories, and EEPROM (electrically erasable programmable read-only memory) is a relatively common, and this memory can achieve erase and data of the original data in the case of power-on. Rewind. (3) Identification The label and the portable data file are different depending on the memory data storage capability in the label, and the label can be divided into two types of labels and portable data files for identification purposes only. For identification tags, a number or multiple digital alphabetic strings are stored in the label, in order to identify the purpose of the purpose or to enter the information management system, the key (KEY). The standard code made in the bar code technology, such as the EAN / UPC code, or mixed coding, or the label user can be stored in the identification tag according to the number of special methods. Identification of only identified numbers stored in the label, for specific identification items, such as people, things, locations, and detailed specific information about the identified items, only in the database connected to the system. As the name suggests, the portable data file is that the data stored in the tag is very large, and it can be seen as a data file. This tag is generally user-programmable. In addition to the stored identification code in the label, there is also a large number of information identified items, such as packaging description, process description, and so on. In practical applications, all information about the identified items are stored in the label, and read tags can get all information about the identified item without being connected to the database for information reading. Further, as the label storage capacity increases, the ability of the tissue data can be provided. In the process of reading the label, the data portion of the data can be achieved in different situations in different situations in the process of reading the label. 2) Signal receiver in the RFID system, the signal receiver is generally called the reader. Different from the supported label type and the completion of the completion, the complexity of the reader is significantly different. The basic function of the reader is to provide a channel for data transmission with the label. In addition, the reader also provides fairly complex signal status control, parity error checks and correction functions. In addition to the stored information that needs to be transferred, the label must also contain some additional information, such as error check information, and the like. The identification data information and additional information are prepared together in a certain structure and transmitted outward in a specific order. The reader controls the transmission of the data stream by receiving additional information. Once the information reaches the reader, the reader determines whether or not the transmitter is retransmitted once via a specific algorithm, or know the transmitter stop signal, this is the "command response protocol". Using this agreement, even in a very short time, a small space is read multiple labels, it is also possible to effectively prevent the generation of "spoofing issues". 3) The programmer only needs to be readable to write label systems. The programmer is a device that is written to the label. The programmer write data is generally offline (OFF-line), that is, the data is written in advance in the label, and the label is directly attached to the identified items on the identified item. There are also some RFID applications, write data is completed online, especially when the production environment is used as an interactive portable data file. 4) The antenna antenna is the transmitting and receiving device of the transmitted data between the label and the reader. In practical applications, in addition to system power, the shape and relative position of the antenna can also affect the transmitting and reception of data, requiring professionals to design and install the system's antenna. 2. The data transfer between the wireless data communication (RFDC) tag and the reader is carried out by the air medium in the form of radio waves. Generally, we can use two parameters to measure data in air media, speed of data transmission, and data transmission distance.
Due to the limited volume of the label, the wireless signal emitted from the label is very weak, and the speed of the signal transmission and the distance of the transmission are very limited. In order to achieve data high speed, long-distance transmission, the data signal must be superimposed on a comparison of signals in a rule change, and the process is called modulation, and the rule change is called carrier. In the RFID system, carrier radio waves are typically issued by a reader or programmer. There are a variety of ways to implement data on the carrier, such as change the wave of the carrier by data information; change the frequency called frequency frequency of the carrier; change the phase call of the carrier and the like. In general, the higher the carrier frequency used, the faster the data can transmit, for example, the carrier of the 2.4 GHz frequency, 2 Mbps (equivalent to about 2 million characters per second) can be transmitted). However, the carrier frequency cannot be improved unlimited to increase the information transmission speed, because the use of radio wave frequencies is subject to government regulation, each country generally specifies different application purposes, RFID technology radio waves This provision must also be observed. Currently, there is generally used communication frequency to communicate with 2.4 GHz spread spectrum technology. This is because the frequency band in my country's 2.4G-2.4835GHz does not need to apply to the National Radio Management Committee to use a public frequency band using a license. In the past, commercial wireless data transmission generally adopted narrowband transmission, which is used to transmit data with a relatively single carrier frequency. Now, the commercial sector uses spread spectrum technology to transmit wireless data, that is, with a range of frequencies transmitted data, this has the concept of bandwidth, the bandwidth is the highest carrier frequency and the lowest carrier frequency in communication. The most obvious advantage of using broadband frequency transmission data is that the speed of data transmission is further accelerated, and the reliability is higher because the information can be transmitted by other frequency carrier lines when a frequency carrier line is busy or fails. The actual commercial broadband transmission data technology can be divided into two types: direct sequence spread spectrum technology (Direct Spance Spread Spectrum, Express Technology) and FREQUENCY HOPPING FH. Direct technology uses a pseudo random code to process the data to obtain the spread spectrum sequence, and then modulate the spread spectrum sequence simultaneously transmitted simultaneously. The signal receiving device decodes the signal after receiving the signal and restructive information according to a specific algorithm. Restore information that can be read. Apply this technique, the system occupies the power spectrum density (transmit power on the unit frequency band) greatly reduces, and the information is extended to a relatively wide frequency range to achieve the purpose of resisting other specific frequency interference. The open bands of my country's non-commitment are consistent with European standards. Refer to European standards, Direct technology can be used from 13 channels (central frequency points), in order to avoid self-interference, the different channels associated with each other, two The frequency is at least 30 MHz between the two. The 13 frequency points are set between 2.412 to 2.472GHz, with a total of 60M bandwidth, usually the Direct system can only select data to transmit data propagation, to a certain extent, the frequency band resources cannot be taken to affect the data. transmission speed. In addition, since data transmission of multiple channels is supported by using the same power, the velocity of the carrier on one channel is relatively small, and the distance from the information transmission is limited.
Frequency and Direct Technology are completely different, and the frequency hopping frequency is controlled by a pseudo-random code, and the frequency bandwidth is constantly hopped in its working bandwidth, and the frequency hopping is equivalent to the instantaneous narrowband communication system, at 2.4-2.4853GHz. The channel is set to 79, and a frequency is hop every 0.02-0.1 second. When jumping into a certain frequency point, first determine whether the frequency is noise interference, if it is not transmitted, if it is notified, it is based on algorithm Skip to the next frequency point to continue judgment. Therefore, in different frequency points, frequency hopping frequency and transmission rates may change, and it is difficult to avoid some unnecessary frequencies, that is, the signal transmission delay is caused when the detection frequency is idle. In addition, since the system has response time limits, exceeds the response time, the frequency hopping device considers the detection signal emission failure (packet loss), will command the transmitter to retransmit, and also cause waste of system resources. Variable frequency technology is characterized by good confidentiality, and anti-interference ability is also better. Compared with Direct Technology, the distance between information transmission is relatively far. The frequency of hopping frequencies in the commercial system is low, and within 50 jumps per second, the cost is low. The primary factor affecting data transmission distance is the strength of the carrier signal and the data signal in the label. The intensity of the carrier signal is controlled by the reader power size. The intensity of the data signal in the tag is self-tabby power (active tag) or label. The resulting power (passive tag) size is determined. In general, the larger the power of the reader and the label, the stronger the carrier signal and the data signal, the farther the data can be transmitted. The radio wave is propagated in the air medium. As the distance of the propagation is getting farther and farther, the intensity of the signal will be weaker. In theory, the degree of attenuation of radio waves is proportional to the square of the transmission distance. It should be noted in the actual application of the system that cannot limit the power of the reader and the label in order to achieve the distance of the data transmission, as in the case of the choice of carrier frequency, the power of radio waves is controlled by the government. In addition to the system power affects the distance of data transmission, the nature and data transmission path of the air medium also affect the distance of data transmission. The properties of the air die include the density, humidity, and the like of the air. In general, the higher the carrier frequency, the more obvious the difference in air properties on the data transmission distance. The greater the humidity of the air, the higher the density of the air, the more severe the absorption of the radio wave, the smaller the distance of the data transmission. In addition, if there are many obstacles in the data transfer path, it also affects the distance of the data transmission because the radio waves encountered an obstacle, and the objects generally absorb and reflect radio waves. Considering the nature of the air and through an obstacle, the degree of radio wave attenuation can sometimes reach four squares proportional to the transmission distance. Factors affecting data transmission distance include, launch, receiving antenna design and arrangement, rogue interference, etc. 5, the classification of the RFID system varies depending on the function completed by the RFID system, can be sorry to divide the RFID system into four types: EAS system, portable data acquisition system, network system, and positioning system. 1) EAS Technology Electronic Article Surveillance (EAS) is an RFID technology set in the door that needs to be controlled. The typical application of this technology is where shops, libraries, data centers, etc., when unauthorized people are illegally taken away from these places, the EAS system will warn. When applying EAS technology, the EAS tag is first paid on the item. When the item is transferred or legally removed, the EAS label is deactivated by a certain device, and the item can be taken away. When the item is equipped with the EAS system, the EAS device automatically detects the activity of the label and discovers that the active tag EAS system will issue a warning. The application of EAS technology can effectively prevent theft of the item, whether it is a large product, or a small item.
