Problems faced by the application of RFID in smart supermarket

1. Introduction

It is applicable to the macro information query and management of supermarkets, and can realize the real-time identification and sharing of commodity information, so as to improve the efficiency of commodity information; Moreover, it can speed up the payment speed of customers, improve customer satisfaction and loyalty, and reduce the risk of supermarkets. This paper mainly discusses the application of RFID technology in smart supermarket.

2. How will smart shelf technology change your supermarket?

2.1 Working principle of smart supermarket

Smart supermarket is a modern supermarket integrating RFID technology, computer communication network and database management technology. It has the advantages of high operation efficiency, low risk cost, scientific and advanced management and excellent service quality. The biggest feature of smart supermarket is the use of RFID technology, which does not need to manually scan the bar code of each commodity, which can save a lot of human and material resources, improve efficiency and avoid the long queue at the exit of supermarket. Because the RF signal can penetrate obstacles such as clothes, it can also prevent supermarket goods from being stolen.

How RFID used in super markets?

Every commodity in the supermarket is attached with an electronic label. The information stored in the label includes the code and price of the commodity. When the RFID tags enters the recognition range of the RFID reader, the tag can be activated immediately, and all information of the product can be obtained by the reader and then displayed to customers and staff. The anti-collision algorithm is adopted inside the reader, which can identify multiple tags at the same time without omission. The smart supermarket based on RFID is not only safe, but also fast, and has great market prospects.

For large-scale smart supermarkets, it is composed of multiple subordinate branches, chain headquarters, distribution centers and other institutions. The headquarters, branches and distribution centers of supermarkets are often located in different geographical locations in a city. Their respective LAN servers need to be remotely connected through the Internet. The intelligent supermarket information management system adopts the distributed database structure: that is, the primary data server is located in the headquarters and the secondary data server is located in each branch. All servers constitute a distributed database system as a whole.
Smart supermarket branch structure: each branch is composed of payment system, purchase system, wireless handheld terminal and management system. The four systems are connected by computer network. The core equipment of payment system, purchase system and wireless handheld terminal are RFID readers and writers. The difference is that the payment system deletes commodity records from the database, the purchase system adds commodity records to the database, and the wireless handheld terminal is used by customers and staff.

3. Related technologies of RFID

3.1 foundation and composition of RFID Technology

Because RFID technology integrates multi-disciplinary technologies such as RF technology, information technology and control technology, it shows a variety of different characteristics and characteristics. According to different classification standards, RFID systems in the market can be classified according to the functions and characteristics of the system.

• (1) According to the energy supply mode, it can be divided into active and passive. An important factor restricting the promotion of RFID technology is cost, so the RFID system in smart supermarket selects passive tags.
• (2) According to the working frequency, it is divided into low-frequency system, intermediate frequency system and high-frequency system. The low-frequency system mainly includes 125kHz and 134.2khz. The frequency of if RF card is 13.56mhz, and the frequency of high-frequency RF card mainly includes 433MHz, 915MHz, 2.45GHz, 5.8GHz, etc. Smart supermarket has strict requirements on the reading and writing distance and speed of RFID, so this design scheme adopts high-frequency RF system.
• (3) According to different modulation modes, it can be divided into active and passive. Since the smart supermarket uses passive tags, its reflection modulation scattering can ensure that the reader can only activate the RF card within the identification range. Therefore, it is most appropriate to choose passive in smart supermarket.

3.2 working principle of RFID

The most basic RFID system consists of two parts: one is the electronic tag, which is used to store information and is the identified object; The second is the electronic tag writer, which is used to read the electronic tag information. Between the electronic tag and the reader, the spatial coupling of RF signal is realized through the combination; In the coupling channel, energy transmission and data exchange are realized according to the time sequence relationship.

How can RFID effectively identify products?

In a typical magnetic field, such as a 915MHz RF system, the role between the reader and the tag can be seen as the radar principle model. After receiving the high-frequency signal sent by the reader, the electronic tag is processed by RF detection, voltage doubling, voltage stabilization and storage circuit to convert it into the working voltage required for the operation of the electronic tag. When transmitting the data contained in the electronic tag, the data signal and if signal are modulated through a mixer (logic gate), and the modulation result is used to control the “impedance switch” of the antenna to change the emission coefficient of the antenna, so that the energy received by the reader and writer presents different amplitudes, so as to complete the modulation and transmission process.

4. Application of RFID in smart supermarket

At present, a large number of people at home and abroad are conducting RFID related research, making many achievements, and successfully applying RFID technology to daily life and production. However, no company has applied RFID technology to supermarket management either abroad or at home. Only Wal mart of France is doing pilot operation in individual supermarkets. Wal Mart has not planned to promote this RFID based smart supermarket in the near future. It is not only because the cost of electronic tags is too high, but also because RFID still has many technical defects in the special environment of supermarkets, and many key problems need to be solved urgently.

4.1 hardware circuit design of reader writer

Reader writer is an indispensable device of RFID system, a tool for data exchange between the system and many mobile electronic tags, and a key link of system operation. Its technical parameters have a decisive impact on the overall performance and reliability of the system. Hardware design is the key to determine the performance of the reader. Its goal is to achieve the requirements of long reading distance, fast recognition rate and 100% recognition rate. It is found that some measures can be taken to improve the performance of the reader. According to the application characteristics of supermarket, we designed a passive backscatter RFID reader. In terms of composition, it can be divided into two parts: RF front-end and digital baseband. Reader / writer structure frame: the RF front-end part includes transmitting circuit, receiving circuit, circulator and antenna; Digital baseband includes DSP and FPGA chips. The transmitting circuit can be subdivided into carrier circuit, modulation circuit and amplification circuit, and its working process is as follows:

• (1) The carrier circuit controls the VCO through the phase-locked loop to generate the carrier frequency (860 ~ 960MHz) and send it to the modulation circuit;
• (2) In the modulation circuit, the mixer mixes the carrier signal and the baseband signal of the reader and writer into a modulation signal, which is sent to the amplifier after low noise amplifier and filtering;
• (3) The reader / writer adjusts the gain of the transmitted signal through the attenuator as required, and the transmitted signal is sent to the reader / writer antenna through the ring after passing through the RF power amplifier.

4.2 data transmission and integrity research how to improve the recognition rate of electronic labels is also one of the research focuses of this topic.

For smart supermarkets, there are many goods. If it takes a lot of time to identify the electronic label of a single commodity, it is still impossible to avoid the phenomenon of long queues at the outlet of supermarkets. The key problem to improve the tag recognition rate is to improve the encoding and decoding and data verification rate of the system. RFID system adopts contactless data transmission, so it is easy to be disturbed in the transmission process, including thermal noise inside the system and various electromagnetic interference outside the system, which will distort the transmitted signal and lead to transmission error. In order to improve the reliability of digital transmission system and reduce the error rate of information transmission, CRC-16 is used to verify the transmitted data. When the received data is found to be wrong, let the data be retransmitted. In addition, some anti-interference measures are adopted to improve the anti-interference ability of the system.

4.3 research on Anti-collision Algorithm

The research on anti-collision algorithm is the most key and difficult problem in the research of RFID system in intelligent supermarket. It is an important factor restricting the application of RFID system in supermarket. Generally, there are a large number of goods purchased by customers from supermarkets. These goods should be accurately and completely identified in the shortest possible time, which is a problem to be solved by the anti-collision algorithm. When the customer pushes the shopping cart into the recognition range of the reader / writer, all electronic labels respond at the same time and collide with each other. An algorithm is needed to recognize these labels one by one from this pile of goods. Therefore, RFID system will adopt certain strategies or algorithms to avoid conflicts, and control the response information of tags to be received by readers through RF channels one by one. The research of anti-collision problem mainly solves two problems: one is how to avoid or reduce the conflict between reader and tag. The second is to avoid or reduce the interference and collision between readers. In order to reduce supermarket costs and improve supermarket profits, passive tags are used in intelligent supermarket system. According to EIC / ISO18000-6, only TypeB tags can be used, so the anti-collision algorithm can only use binary algorithm. Binary search algorithm is the most commonly used anti-collision algorithm of RFID system. Its algorithm is very flexible and will not fail to prevent collision. When n labels conflict, it only needs a certain number of anti-collision cycles to accurately identify the appropriate labels. The basic idea of this algorithm is that the reader / writer determines the data conflict location generated when the tag serial number is sent, and then forcibly commands those tags with the information of “0” or “1” sent at the conflict location to exit the conflict. When n-1 transponders exit the conflict, the channel will be fully occupied by the remaining tag and recognized by the reader / writer.

5. Conclusion

Because RFID has the advantages of fast speed and long distance, RFID technology can be successfully applied to supermarket management, improve supermarket management level and reduce supermarket operation cost. After investigation, 915MHz frequency band is selected as the main frequency of the reader and writer, which can be quickly identified from a long distance. The purchase system is installed in the supermarket warehouse and the payment system is installed at the supermarket exit, which is connected with the management system through the computer network, so as to form a complete supermarket management system.

Source: China RFID Retail Solutions Provider – Actility Technologies Company Limited (www.tractility.com)

Actility provides powerful security solutions for retail store management to prevent asset and property losses, improve transaction security, and provide intelligent analysis. We produce AM/EM/RFID systems, EAS tags, EAS soft tags, EAS safer, lanyards, detachers and all kinds EAS accessories products. Infrared people counter and camera people counter is available. If you want to have more information about the article or you want to share your opinion with us, contact us at [email protected]