The Design And Implementation Of Active Rfid System

RFID (Radio Frequency Identification) technology is a technology of target recognition and localization derived from the technology of radar in the1950’s and has developed rapidly since the1980’s.The technology is mainly used for non-contact two-way wireless communication, so as to obtain the characteristic information of the target object to achieve the purpose of identification and localization. RFID technology, because of its features of contactless, non-line, high degree of accuracy, low-cost and convenient to extend etc, has become the first choice of indoor positioning technology solutions. There are many different kinds of RFID positioning methods, RSSI (Received Signal Strength Indication) is a very common one, but this method has low localization accuracy and is vulnerable to environmental interference. Therefore, this thesis designed an indoor localization system combining ultrasonic and RF technology by using TOA (Time Of Arrival, arrival time) localization method to identify and locate active electronic tags. The localization system takes full advantages of the RF radio and ultrasonic localization to improve the localization accuracy.This system adopts the UHF radio frequency433MHz, which is more common in the logistics field, and21KHz ultrasonic frequency. Because the two have6orders of magnitude difference in air speed, their arrival time difference can be the ultrasonic propagation time between the tag and the reader, and then multiplied by the speed of sound to get distant information, thereby performing localization.The work of the thesis includes both hardware and software designs. The work of hardware includes the main chip selection, schematic design, PCB (Printed Circuit Board) design and welding components. Micro control unit module chooses the low-power MSP430G2553and RF module chooses the low-power CC1101. System hardware includes the control unit, power supply module, RF transceiver module, ultrasonic transmitting module, ultrasonic receiving module and RS232serial interface module. In the aspect of software, it uses C language to complete each module drivers and radio communication protocol packets design, and C++to finish the design of localization algorithm and graphical display program. Localization algorithm adopts TOA localization algorithm, and uses the algorithm of three-sphere intersect at one point for the calculation of coordinates of point. The MFC program in upper machine implements the serial communication function and graphical display function, the develepment environment is Visual Studio2010. Upon completion of the system, a number of indicators have been tested, including the ultrasonic range accuracy test, the radio communication protocol test and the system localization accuracy test. The results show that the designed indoor localization system based on radio and ultrasound localization has high localization accuracy, the communication distance is appropriate, which can basically meet the design requirements.