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According to the technical characteristics of RFID, this solution applies RFID to the intelligent warehouse management of supermarkets; and combines RFID technology with wireless sensor networks. As a sensor node of the wireless sensor network, the RFID system, together with other sensor nodes, such as fire and anti-theft sensors, can form a comprehensive intelligent supermarket monitoring system. This provides the possibility for the supermarket shelf management to further reduce the additional cost of goods as much as possible, and increases the supermarket’s competitiveness in the market. In practice, the RFID application system has certain reference value and practical significance.
The overall frame design of the system
In view of the characteristics of the intelligent warehouse management of large super coins, the system mainly includes: RFID identification system, wireless sensor network, interaction between RFID identification system and wireless terminal.
2.1 RFID radio frequency identification system
The main function of the reader is to read and write data to the transponder through the antenna and communicate with the upper computer. It generally contains a radio frequency module, a control unit and a coupling element connected to the transponder. In addition, the reader has an additional interface to transfer the obtained data to another system.
The reader hardware system is mainly composed of 4 parts: interface circuit, control unit, radio frequency module, antenna, as shown in Figure 1.
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Figure 1 Block diagram of the hardware system
The upper computer is connected with the control unit of the reader through the interface circuit, and sends commands such as read/write card to the control unit, and receives data and operation reports from the control module. The control unit is connected with the radio frequency module, and the main program running on the control unit controls the operation of the radio frequency module according to specific conditions. The radio frequency module modulates the data and sends it to the transponder through the antenna, and demodulates the transponder return signal received from the antenna.
The reader radio frequency module adopts the FM1725 contactless IC card chip of Fudan Microelectronics Company, which completes the functions of data modulation and demodulation, and rectifies and transmits the radio frequency modulation signal. The transmitter part inside the FM1725 chip can directly drive the antenna at a short operating distance without adding an active circuit, while the receiver part provides a reliable demodulation and decoding circuit. Its digital processing part converts parallel data into serial, supports checking the generated frames, generating and checking parity and CRC, as well as bit coding and processing. In addition, FM1725 also provides an SPI compatible interface, and its parallel interface can be directly connected to an 8-bit MCU.
The control unit of the reader adopts the high-performance 8-bit single-chip AT89S52 produced by ATMEL Company, which is mainly responsible for running the program of reading and writing the card, providing the control signal of the FM1725 chip, and completing the data communication with the upper computer or the network through the RS232 interface. The single-chip microcomputer contains 8K bytes of Flash read-only program memory, and its space is large enough to write programs that drive and control the FM1725 radio frequency chip. There is no need to connect other external storage devices, which simplifies circuit design and improves circuit reliability.
The radio frequency card adopts the passive Mifare standard IC card MF1 IC$50, and there is 8K EEPROM in the card. It is the storage carrier of data, and the data is read and written through the antenna of the reader.
Figure 2 Basic operation process
The basic operation process is shown in Figure 2. The user first writes information into the MF1 IC$50 card through the reader. When an MFIIC$50 card enters the reader’s antenna working range, the card is activated and the reader sends a data read signal to the card. The card reads the data according to the received data. The signal sends the data specified in the storage unit to the reader through the antenna, and the reader sends the data to the host computer or network through the RS232 interface.
2.2 Wireless sensor network
The wireless sensor network is composed of many wireless sensor network nodes deployed in the monitoring area. Its purpose is to cooperatively sense, collect and process the information of the sensing objects in the geographic area covered by the sensor network, and pass it to the observer through Ad hoc. .
2.2.1 Sensor node
The wireless sensor network node mainly completes the data collection, processing and transmission functions, and is usually composed of 4 units. See Figure 3.
Figure 3 The composition of wireless sensor network nodes
In the wireless sensor network node, the micro control unit uses TI’s MSP430F19 microcontroller, and the wireless transmission unit uses the IA4420 chip from Integration Associates.
1) Micro control unit. TI’s MSP430 series is a 16-bit hybrid microcontroller with reduced instruction set and ultra-low power consumption. In the wireless sensor node. 2) Wireless transmission unit. The core chip used by the wireless transmission unit is IA4420o, which is a programmable, low-power, multi-channel frequency shift keying (FSK) full-duplex radio frequency transceiver chip launched by Integration Associates. IA4420 can work in the ISM (industrial, scientific, medical) frequency bands, which are 315, 433, 868 and 915MHz respectively. The chip’s working voltage is 2.2-5.4V, low-power consumption mode, standby current of 0.3uA, FSK modulation mode, adjustable transmission power of 5-8dBm, and the measured transmission distance in an open outdoor area is more than 200m.
2.2.2 Wireless sensor network protocol
The media access control protocol is abbreviated as the MAC protocol, which is in the bottom part of the wireless sensor network protocol to solve the problem of how nodes in the wireless sensor network share media to ensure a satisfactory network and performance.
The MAC protocol has a great impact on the performance of wireless sensor networks. It is one of the key network protocols to ensure the efficient communication of wireless sensor networks. The performance of sensor networks such as throughput, delay, and performance depends entirely on the adopted MAC protocol. Cellular phone network and Ad-Hoc are the current mainstream wireless network technologies, but their respective MAC protocols are not suitable for wireless sensor networks. The media access control in GSM and CDMA is mainly concerned with how to meet the user’s Qos requirements and save bandwidth resources, and power consumption is the second priority. Ad-Hoc network considers how to establish links between nodes in a highly mobile environment, while taking into account certain QoS requirements, and power consumption is not its primary concern. The primary consideration for the MAC protocol of wireless sensor networks is to save energy. This means that the MAC protocol of the traditional network is not suitable for wireless sensor networks, and a new MAC protocol suitable for wireless sensor networks needs to be proposed.
Aiming at the application of the IA4420 chip in wireless sensor networks, Integration has proposed a new MAC layer protocol-the protocol framework of the EZMac protocol. EZMac is a MAC layer protocol based on the C language. It provides a simple physical layer interface between nodes for the application design of wireless transceivers, and manages the transmission of signals and the transmission of related data packets from the sender to the output end.
The data packet of EZMac is small and supports data transmission using the internal baud rate generator of the transceiver chip. The state machine action of EZMac is determined by a set of parameters stored in different registers. The MAC engine supports 4 basic modes: sleep, idle, transmission and reception. The sleep mode consumes the least energy, the idle mode takes the second place, and the transmission mode consumes the most energy. These 4 modes can be realized through 9 basic states. The 9 states are: sleep, wake up, idle, detect DQD (data quality detection), receive packet, packet valid, listen, transmit packet, transmit information Mistake. The state transition flow chart of EZMac is shown in Figure 4.
Figure 4 EZMac state transition flow chart
2.3 The interaction between the wireless terminal and the RFID system
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