The signal transmission and measurement methods of the passive UHF radio-frequency identi¿cation (RFID) system are discussed in this paper. Parts of tag's communication performance, which conform to the ISO/IEC 18000-6 Type C, are obtained by using the software-defined radio test platform. The received power by the platform changes when the communication parameters vary. The measurement results show that the small Tari, half duty cycle and higher modulation index in baseband signal coding allow the RFID system to receive larger power, also allow the RFID system to get larger read range. Index Terms-Radio-Frequency IDenti¿cation(RFID), passive tag, sensitivity, performance test I. INTRODUCTIONRadio frequency identification(RFID) is an automatic identification and data capture technology that gained much attention in last decades. Several standards provide the RFID products' communication parameters such as coding, modulation-demodulation, anti-collision algorithms, and other details. The change of the parameters and environment variables will lead to RFID communication performance changing. The performance measurement on RFID system includes tag test, reader test and system test, but most of tests focus only on the link budget. Kim used two isolated reader antennas to transmit continuous wave and to receive the backscattered signal in office. They adopted small scale fading model to simulate the up-link and down-link of RFID communication process and verified the path loss of bidirectional link is double that of single link[1]. Read range of several types of RFID tags that mounted on different surface such as metal and plastic bottle filled with water were analyzed[2,3].They verified the decline in electric field near an object's surface leading to the decrease in read range, and interpreted the correlation between read range and gain, frequency, impedance, polarization on the resonance frequency. That the tag sensitivity, antenna gains, polarization, impedance mismatch, path loss effect on read range was analyzed [4].The link power were tested through the National Instruments LabVIEW-controlled PXI RF hardware [5].All tests were obtained under fixed communication parameters as Tari, modulation depth, operating frequency,etc. By varying these parameter values, the performance and operation value of the RFID communication are changed.

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The radiation field of a typical UHF RFID portal application was measured using our developed LabVIEW based automatic test platform. Path loss exponent and standard deviation of Log-normal shadowing model were obtained through MMSE criteria from measured data. Rician and Rayleigh empirical models were also introduced to predict the probability of blind spots. And fade margins were successfully compared for different blind spots probability.

Optimal conditions for maximizing the effectively received power of reader receiver in passive ultra high frequency radio-frequency identification system are analyzed in this paper. The mismatched impendence affecting modulation index of tag backscatter link is discussed. Expressions of backscattered modulation indexes for calculating normalized effective received power of reader receiver, lower boundary of signal-to-noise ratio for demodulated output signal, and bit error rate are derived. Modulation indexes of backscatter link under different parameters are measured in open indoor environment. The measurement results show that the tag can be detected successfully when the modulation index of backscatter link is in a range from 5% to 10%.

The discrimination of passive Ultra High Frequency (UHF) Radio Frequency Identification (RFID) system can be affected by several factors. To measure the discrimination of UHF RFID systems, a measurement system based on virtual instruments which can adjust the speed, position and angle of tag is built in this paper. The learning vector quantization neural network based on genetic algorithm (GA-LVQ) is introduced to predict the discrimination of UHF RFID systems. To enhance the searching efficiency, the GA is modified adaptively. Prediction results are found to be good in agreement with experimental data.