Study On Code-decode And Data Verification Problem In UHF RFID System

Because of a long communication distance of the Ultrahigh Frequency(UHF) Radio Frequency Identification(RFID) system, there are have several problems: channel attenuation,signal multipath interference and anti-collision of multi-tags communication etc. Moreover it always working in a hostile environment, its working frequency is a royalty-free Industrial, Scientific, Medical (ISM) Band. In this frequency band, the readers is easily interfered by the noise comes from mobile phone, cordless telephone, wireless headset, wireless data network and other short distance radio equipments. Therefor the security and reliability of the UHF RFID system cannot be ensured, and seriously affect its large-scale commercial applications. Based on above reasons, it's of great significance to the research and improvement of UHF RFID system,especially the design of high speed and high recognition rate of the UHF RFID system has more challenging and more practical application values.The first, this paper investigates the forward link and return link data encoding method in short range communication types A and B in ISO/IEC18000-6, and deeply analyzes encoding method and technical parameters of Bi-Phase Space(FM0)coding, Pulse Interval Encoding(PIE)coding and Manchester coding. We also designed and simulated code circuits and decode circuits of the three encoding method by FPGA experiment platform. The second, We discussed the technical principle of error control of the UHF RFID system, especially for the technology of data verification and calibration, namely cyclic redundancy check that used in ISO/IEC18000-6. The circuits of CRC based on Linear Feedback Shift Register (LSFR) are analyzed from theory and realization, and some means of solving problems are put forward, then an improved LSFR circuit to implement CRC is designed. For some require fast CRC calculation system, we designed a novel parallel CRC circuit by using recursive formula. In the end, we put forward a novel digital baseband circuit of UHF RFID system, it different from common digital baseband circuits is that adds a convolutional coding & Viterbi decoder module between data encoding module and CRC module. Making use of convolutional coding's powerful error correction capability to improve the low recognition rate and slow speed of UHF RFID system in the environment full of electromagnetic interferences, achieved good effect.