Complete link budget for forward and backward link in a RFID system are given with constituent parts. Backward link signal levels with current improvements requires separate TX and RX antenna bistatic configuration to overcome reader threshold. To further elaborate on 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. It is demonstrated that both forward and backward links have limitations on the range depending upon tag power dissipation, antennas in use and type of modulation. To make two distances equal, parameters are found from two way link equations. Then, 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.
RFID, RFID link budget, reflection coefficient, transmitted power, reflected power, ASK and BPSK bac