Patent ID: 7787568

Claim:
A radio frequency identification (RFID) reader, comprising: a demodulator configured to demodulate a received quadrature modulated radio frequency signal to an in-phase signal component and a quadrature-phase signal component that contain a current data symbol; a decision module configured to determine a closest point of M previously generated corrected constellation points to the in-phase signal component and the quadrature-phase signal component; a demapper module configured to demap the determined closest point to a data value for the current data symbol; a corrected reference signal generator configured to receive the determined closest point, the in-phase signal component, and the quadrature-phase signal component, and to generate a corrected in-phase reference signal and a corrected quadrature-phase reference signal; an average signal generator configured to receive corrected in-phase reference signals and corrected quadrature-phase reference signals generated for each of S data symbols including the current data symbol, and to generate an averaged corrected in-phase reference signal and an averaged corrected quadrature-phase reference signal; and a corrected constellation points generator configured to receive the averaged corrected in-phase reference signal and the averaged corrected quadrature-phase reference signal, and to generate a current corrected constellation having M current corrected constellation points, wherein each of the M current corrected constellation points is defined by an I coordinate and a Q coordinate.