Chinese Journal of Computers   Full Text
Title	Energy Efficient Physical Layer Design for Passive RFID System
Authors	WANG Hong-Gang PEI Chang-Xing YI Yun-Hui
Address	(State Key Laboratory of Integrated Services Networks, Xidian University, Xi’an 710071)
Year	2009
Issue	No.7(1356—1364)
Abstract &   Background	Abstract In forward link, to cooperate with ASK modulation, a new data coding method for carrying out more energy to passive tag is presented for passive RFID system in this paper. The basic idea of the coding is to set adjustable and asymmetric high and low level duration within a symbol cycle, and a longer duration for high level. The performance analysis results show the energy of baseband data transmitted from reader to tags increased by 84% at most, compared with that of Manchester coding at typical 40kbps. The system performance can be increased by using this coding. The same results are showed by the testbed and theoretical analysis. In return link, the scheme of coded OOK and coded BPSK is proposed. The cutoff rate is used to study the influence of encoding on system performances. Analysis results show that coded modulation is more energy efficient than uncoded modulation in Passive RFID return link and the system performance is improved with almost no increase in chip complexity. The gains of encoding in system information rates and communication range for different cutoff rate is analyzed and evaluated. Keywords RFID(Radio Frequency Identify); data coding; cutoff rate Background In passive RFID system, tags have no internal power and obtain energy from the RF wave transmitted by the reader. Thus the power received by the passive tags is an important limitation of passive RFID system performances (for example, communication range and information rate). There are three types, type A, B and C, in the UHF RFID standard ISO/IEC 18000-6. In forward link (reader-to-tag), the data encoding in type A and C is PIE (Pulse interval encoding), and the data encoding in type B is Manchester coding. For carrying out more energy to passive tag, a new data coding method in forward link is presented in this paper. In real RFID environments, the power received by tag and reader decrease greatly for multipath fading. Although the reader is not sensitive to it now, there must be a critical value of chip sensitivity that reader can write information into tag but not read out information from tag when the chip sensitivity is lower than this critical value for the backscattering power is not enough for reader receiver to work normally. For this case, the reader receiver sensitivity is also a limitation on RFID readability, and coded modulation in tag side will be a good choice to degrade the receiver sensitivity besides the optimal RF design. In return link (tag-to-reader), the data encoding in type A and B is FM0. In type C, tags encode the data as either FM0 baseband or Miller modulation of a subcarrier at the data rate. The backscatter shall use ASK and/or PSK modulation, and the coded modulation schemes are not taken into account. So, the scheme of coded OOK and coded BPSK is proposed in this paper. The gains of encoding in system information rates and communication range for different cutoff rate is analyzed and evaluated. Simulation and test results show that the system performance can be improved efficiently by the proposed physical scheme. This work was supported by the National Natural Science Foundation of China (No. 60572147), Xi’an Industrial Science and Technology Project (No.YF07015), the 111 Project (No.B08038), and State Key Laboratory of Integrated Services Networks (No.ISN02080002). The group has published highly research papers in the fields of RFID, WSN and wireless networks.