"As the IoT research and wireless sensing network technology rapidly, ZigBee technology acts as an emerging low cost, low power, low-rate short-range wireless sensing network technology, is based on IEEE802.15.4 standard development wireless The agreement .ieee802.15.4 is responsible for the physical layer and the MAC layer, and the ZigBee alliance is responsible for the development of network layers and application layers. Using ZigBee technology to achieve low cost, low power consumption, and the signal transmission is not affected by the sienet Applications in environmental monitoring, industrial site acquisition, smart home and medical care.
RFID (RFIo Frequency Identification, RF Identification) is a technique for achieving non-contact information transfer through spatial fusion (alternating magnetic field or electromagnetic field) and through the transmitted information to automatic recognition purposes. The advantage of the RF identification card is its non-contactability, so it does not have to manually intervene during completion of the identification, suitable for automation, can identify high-speed moving objects and can simultaneously identify multiple radio frequency cards, and quick and easy. RFID technology is a new technology application area, which covers only RF technologies, as well as radio frequency technology, cryptography, communication principle, and semiconductor integrated circuit technology, is a multi-disciplined emerging discipline. Therefore, the understanding and research of RFID technology has far-reaching theoretical significance.
At present, indoor positioning mainly has ranging techniques and non-gauge techniques, and the positioning algorithm based on ranging is AOA, TOA, TDOA, RSSI; the positioning algorithm based on non-measuring technology, mainly: DV-Hop positioning algorithm, quality algorithm , Convex planning positioning algorithm, etc. Based on the positioning mechanism of the ranging is relatively high, in a high-density network composed of low power wireless devices, the TDOA estimation is difficult to implement due to synchronization between the devices, using AOA, TDOA estimation. Although the distance can be estimated by measuring TOA, multi-diameter and noise, as well as the inclusion of the reference clock, the effect of the distance estimate will be deteriorated; the positioning algorithm based on the non-velocity is not required to measure the Jedi information and angle information between the nodes. It is the location of the network connectivity to calculate the node, but the positioning is low. Based on RSSI-based distance estimation, you can measure it by the sensor node itself, no additional hard support. The RSSI adds additional valuable information compared to the algorithm for connecting information. Therefore, RSSI-based ranging is a method of common use of wireless sensing networks. I use RSSI-based ranging technology, the indoor positioning system that is fused with RFID and ZigBee technology, which effectively improves indoor positioning, and realizes the positioning of the room.
1 Overall design of the positioning system
The design of this system has five components, including host machines, gateways, base stations, electronic tags, reference nodes. The function of the host computer is to monitor and manage the entire system. The structural block diagram of the positioning system is shown in Figure 1.
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The function of the gateway is served by the coordinator. It plays a crucial or so in the entire system. First, it should respond to the command issued by the host computer, turn on the network, wait for other types of nodes to enter the network, but also receive each node Uploaded data and transmitted to the host computer software. The base station consists of the ZigBee module and the RFIDReader module. They transmit data by RX / TX. The function of the base station is to receive the message sent by the host computer during the positioning process, form a radio frequency signal in modulation, and constantly passing the antenna. The radio frequency signal is transmitted outward; the ZigBee module can also be used as a reference node, and it is possible to send its own coordinate information and the RSSI value to the blind node. The electronic tag is composed of ZigBee modules and RFID TAG modules, which are directly connected via the SPI interface. It functions is to receive the radio frequency signal sent by the base station. After demodulation and decoding, the data is transmitted to the zigbee module by the SPI mode, and the ZigBee module is sent to the gateway in the way. The ZigBee module has another effect, which is arbitrary as a blind node that can be moved in the area surrounded by the reference node. It constitutes a positioning system with the reference node and the gateway. The reference node only has only one ZigBee module, which is a node of stationary, known self-position coordinate information, which is functional to send its own RSSI value and location coordinate information to the blind node.
2 hardware design of the positioning system
2.1 gateway
The design of the gateway consists of two parts, namely wireless communication modules, and auxiliary function modules. The wireless communication module is part of this gateway, responsible for communicating with the base station, electronic tag, and reference node, and the like. The auxiliary function module is completed the positioning serial port communication, status indication, LCD display, power supply and other auxiliary functions. The structural block diagram of the gateway is shown in Figure 2.
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2.2 base station
The design of the base station includes two parts, the RFID Reader module, and the ZigBee module. The RFID Reader module is mainly composed of the microcontroller and matching circuit of PIC16F887. Both the RFID Reader module and the ZigBee module are transmitted via RX / TX. The block diagram of the base station is shown in Figure 3.
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The host computer sends a command, the gateway transmits information such as the exciter ID wirelessly to the zigbee module in the base station. The ZigBee module sends the information such as the exciter ID to the microcontroller ID to the microcontroller PIC16F887 by RX / TX. The microcontroller is generated by outputting the PWM signal. The carrier of the frequency 125 kHz and the information such as the exciter ID is modulated on the 125 kHz carrier in the 125 kHz carrier, where the data encoding is encoded by Manchester, and then transfers to the power of the drive TC4422, through the antenna constant direction 125 kHz incentive signals are sent. When there is a RFID TAG module approaches the area, it is awakened, the microneedizer is sent to the RFID TAG module in the form of the Manchester code by the control piece select signal CS. The ZigBee module can be transmitted with RFID Reader, and can also be used as a reference node to send their coordinate information and the RSSI value to the blind node in the electronic tag.
2.3 electronic label
The electronic tag design includes RFID TAG modules and ZigBee modules. The RFID TAG module is mainly composed of an AS3933 front-end analog chip and matching circuit, and the ZigBee module is composed of RF chip CC2530 and matching circuit. They are transmitted through the SPI interface. The CC2530 configures AS3933 via the SPI interface, and the detailed pin connection is shown in Figure 4.
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The RFID TAG module receives the 125k excitation signal sent by the base station, and then demodulate the excitation signal through the AS3933 chip, and decodes the Manchester code, by configuring the associated register of the SPI bus, when Wake is "1" The CC2530 in the ZigBee module reads the data from the DATA in the AS3933, and then packages the data packet wirelessly to the gateway through the antenna, and the host machine is sent according to the exciter ID. And the electronic tag ID determined, you can know that the electronic tag is located in a certain exciter, and the ZigBee module is transmitted from the RFID TAG module, and can be used as a blind node, which constantly sends a positioning request to the reference node, thereby obtaining a reference node The coordinate information and the RSSI value, then calculate its own coordinate information and RSSI values by calling the positioning algorithm, the wireless transmission to the gateway, sending the data to the host computer, and can know the location of the electronic tag according to the coordinate information. The RFID TAG module is mutually matched with the ZigBee module to achieve more area positioning and room level positioning.
2.4 Reference node
In this design, there is a separate reference node module and the ZigBee module on the base station can also be used as a reference node. The design of the reference node includes two parts, which are wireless communication modules and auxiliary functional modules, respectively. The parameter configuration of the especially the serial communication module in the reference node receives the gateway: collecting the RSSI value when the blind node communication is collected, and calculates its average; the average value of the coordinate information and the RSSI can be transmitted. The auxiliary function module contains 3 parts, which are indicative modules, buttons, buttons, and power supply modules, respectively. The indication module is an indication of the positioning state; the button module is the joining and binding network; the power supply module is responsible for power supply to the entire reference node. The structural block diagram of the reference node is shown in Figure 5.
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3 positioning process of the positioning system
The basic idea of the positioning system is that after the system is configured for the reference node and the blind node node, the blind node is waiting for the gateway to send a positioning request. After the blind node receives the positioning request sent by the gateway, it began to send a series of RSSI. BLAST information is broadcast, and the reference node receives the RSSI BLAST data sent by the blind node and saves its RSSI value. After waiting for the blind node configured to complete the specified time interval, the blind node sends the XY-RSSI request broadcast to the reference node, each receiving the reference node that receives the RSSI BLAST information broadcast, will calculate the received RSSI value and according to the RSSI value of the request. And the RSSI value of the previous RSSI BLAST calculates the average, send the XY-RSSI response to the blind node, the blind node receives the XY-RSSI response, the reference node will send its own coordinate information and the RSSI value to the blind node. After the blind node receives these parameters, according to the positioning algorithm, the coordinate information is calculated, and the calculated coordinate information is sent to the gateway, and the gateway sends data to the PC through the serial port. The positioning timing of the positioning system is shown in Figure 6.
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4 experimental results analysis
After the positioning software is designed, the hardware platform is set, and the positioning of the 810 laboratory room is positioned. The red circular point represents the fixed reference node position, the yellow square point represents the actual position of the electronic tag, the pink rectangular representative is placed in the base station, the blue-colored triangle represents the location of the host monitoring software. We placed four reference nodes in the room, and the coordinates were (0, 0), (0, 5), (5, 5), enclosed into a 55 region, and recorded the coordinates of electronic tags. Location; the positioning image is shown in Figure 7 (a). Keep the electronic label point does not move, add a reference node to record the coordinates again; the positioning image is shown in Figure 7 (b). Continue to keep the electronic label does not move, add a base station at the door of the room. Record its coordinates. The positioning image is shown in Figure 7 (c).
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By observing the positioning image of Figures 7 (a), 7 (b) without increasing the base station, it can be found that the measurement value monitored by the host computer is getting closer to the actual value as the reference node increases. Within the range, as the reference node increases to be positioned. In the same reference node, a base station is added at the door of the room, and the positioning image of Fig. 7 (c) is observed, and it is found that the measured value monitored by the host machine is closer to the actual value than the measured value monitored in Fig. 7 (b). . Since there are both RFID READERs on the base station, there is a reference node. So not only increase the positioning, but also determine the specific location of the electronic tag. This shows that the RFID and ZigBee are well combined, it can improve the positioning of the room area, and achieve the location of the room level.
5 Conclusion
In the text, it is mainly introduced by the hardware design, an indoor positioning system based on RFID and ZigBee technology, a detailed introduction of the hardware of the positioning system, and analyzes the positioning system software flow. By reasonable arrangement of reference nodes and base stations, measurement in the indoor environment, within the positioning module communication range, by increasing the number of reference nodes, the number of efficient ways such as the base station, can be effectively improved. Through experiments, the design scheme fused through RFID and ZigBee technology can not only reach 1m, but also the indoor room level is also achieved. The hardware device of the program requires low, high positioning, which meets market demand. The design of the indoor positioning system based on Zig BEE and RFID can be used well in the intelligent building, underground garage, medical care.
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Source: Wiku Electronic Market Network
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