Passive RFID the Forward and Backward Link Budgets and Comparison of ASK and BPSK Backscatter Modulations

Reflected signal levels in passive RFID require seperate TX and RX antennas to overcome the reader threshold. Using latest improvements, it is shown in this work that both the forward and backward links restrict communication distance given with equations depending upon tag power dissipation, antennas in use, type of modulation and operating environment and parameters to make both distances equal are given. Complete link budget for the forward and backward links in a RFID system are given with constituent parts in detail. After that, to further elaborate on the link budgets, reflection coefficient and power equations are obtained from a RFID front-end model with circuit theory and shown on a passive RFID system. This study shows modulation index m and antenna gain Gt for BPSK and ASK modulations to make two distances equal for the environment to be within, found from two way link equations. Also, ASK and BPSK modulations are compared on communication distance for given average backscatter difference power, minimum SNR to targeted BER on the reader by the equations obtained on the circuit model and MATLAB simulations.

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