说明：  A system simulation environment in Matlab/Simulink of RFID is constructed in this paper. Special attention is emphasized on the analog/RF circuit.Negative effects are concerned in the system model,such as phase noise of the local oscillator,TX-RX coupling,reflection of the environment, AWGN noise,DC offset,I/Q mismatch,etc.Performance of the whole system can be evaluated by changing the coding method,parameters of building blocks,and operation distance.Finally,some simulation results are presented in this paper.