The Research On The Base-band Signal Frequency Offset Detection On Uhf (ultra High Frequency) Rfid (radio Frequency Identification)

Radio Frequency Identification (RFID) has become the wide-spread contact-free automatic identification technology in many services. A typical RFID system consists of two basic elements: Reader and Tag. Compared with bar-code card and magcard, the advantage of RFID such as reading-speed quick, contact-free, memory capacity large and anti-interference, the reading distance far, cause it to become identification development direction.The performance of RFID is impacted with many parameters such as adhere object type, speed of conveyor, the interaction of product and tag placement. Along with the standard's development and establishment the RFID product testing to in order to guarantee the product quality in compliance with the standards. The RFID Base-band frequency offset test is an important content of the testing.The high-frequency Signal that backscattered from a Tag is received by Reader's antenna and goes through certain signal processing (such as amplification, quadrature down conversion), Then, we get the base-band signal. RFID standards have different frequency offset requirements for base-band signal under different rate and temperature. This requires frequency offset measurement for RFID base-band signal.This paper has complicated the theoretical Design of RFID Base-band Frequency Offset Detect.This paper takes the method based on FIR. First carrying on lowpass filtering for the sampled data, then throught the correlation to decode data, finally, the following method are used to estimate frequency offset.For the frequency offset estimation under ambient noise known, it can be obtained by pre-set threshold. In view of frequency offset estimation's sensitivity to the point count on the same level, the border point must be carefully decided. Comparing the border point with pre-set threshold to sure weight, then comparing the estimated result with the sampling points in different frequency offset to determine the frequency offset; For the frequency offset estimation under ambient noise unknown, it can be obtained by wave translation. Extract and arrange the sampled data to form four-times sampled signal of cos, at last gets offset through power spectrual density analysis.The simulation under MATLAB shows that: under the best measurement length, if SNR>3dB, the accuracy rate of pre-set threshold algorithem achieve above percent 93. When the survey length is bigger than 100 codes, the accuracyrate of wave translation algorithem's method rate of may achieve above 99%.