LINK BUDGETS FOR BACKSCATTER RADIO SYSTEMS
Backscatter radio is a term that refers to systems that communicate wirelessly by scattering electromagnetic waves. Such systems have found application in many radio-frequency identification (RFID) and passive sensor applications. In a typical backscatter radio system, a small, low-power transponder, or radio-frequency (RF) tag, communicates with an interrogator, or reader, by modulating the waves scattered from its antenna. While this communication method allows the transponder to communicate while consuming very little power, system design is challenging because of the complex electromagnetic interactions between the reader, RF tag, and the radio channel. These interactions affect backscatter radio performance by limiting the amount of power received by the RF tag and/or the amount of modulated power backscattered to the reader. If either of these powers drop below a certain threshold, RF tag operation will cease and/or the reader will be unable to reliably detect the backscattered signal. Therefore, it is extremely important for the design and operation of modulated backscatter systems that these received powers be predicted. This chapter, which has been adapted from Griffin and Durgin  and Griffin , describes two radio link budgets ...