Investigation of radio link budget for UHF RFID systems

Radio link budget is a determinant factor for the coverage estimation of wireless communication systems. Various studies have been made to model the radio link budget of passive Ultra-High Frequency (UHF) Radio Frequency IDentification (RFID) systems, which operate in dyadic channels. These studies generally either ignore or make simple assumptions on the backscattered-transmission loss due to the circuit of an RFID tag. However, we observed that the loss could vary nonlinearly with the incident power to the tag due to the impedance characteristics of the RFID microchips. Such nonlinear loss can result in discrepancy between the estimated and the actual link budget. Our experiments showed that link budget estimated without considering the nonlinear transmission loss can differ significantly from the actual one.