Patent ID: 8638255

Claim:
A reader device for reading information transmitted from a transponder via a backscatter signal generated by the transponder in response to a stimulus signal generated by the reader device, the reader device comprising: a first power estimation unit configured to estimate a first power value indicative of power of the stimulus signal at a position of the transponder by evaluating power information included in the backscatter signal; a second power estimation unit configured to estimate a second power value indicative of power of the backscatter signal at a position of the reader device; a distance estimation unit configured to estimate a distance between the reader device and the transponder based on the first power value and the second power value, wherein the first power estimation unit is configured to estimate the first power value by evaluating the backscatter signal based on a predefined nonlinear transfer function of an available power versus modulation efficiency by which the stimulus signal is manipulated by the transponder or evaluating a clock rate of the backscatter signal manipulated by the transponder.