Patent ID: 7916671
Filing Date: 2011-03-29
Classification: H04B,H04L

Abstract:
1. A method of canceling echo in a frequency division duplex (FDD) radio, the method comprising: receiving a transmitter in-phase baseband signal and a transmitter quadrature-phase baseband signal to be upconverted and transmitted by a transmitter of the FDD radio in quadrature amplitude modulation using a transmitter local oscillator (Tx LO) signal; mixing a transmitter local oscillator (Tx LO) signal and a receiver local oscillator (Rx LO) signal to generate a separation frequency signal having a frequency corresponding to a difference in frequency between the Tx LO signal and the Rx LO signal; upconverting in quadrature the transmitter in-phase baseband signal and the transmitter quadrature-phase baseband signal using a first phase and a second phase, respectively, of the Tx LO to generate a transmitter QAM signal, wherein upconverting is performed by a transmitter of the FDD radio; receiving a receiver QAM signal, wherein receiving is performed by a receiver of the FDD radio; downconverting the receiver QAM signal in quadrature using a first phase and a second phase of the Rx LO signal to generate a receiver in-phase baseband signal and a receiver quadrature-phase baseband signal, respectively; generating a first echo copy signal wherein the first echo copy signal comprises a first product of mixing of the transmitter in-phase baseband signal and a first phase of the separation frequency signal; generating a second echo copy signal wherein the second echo copy signal comprises a second product of mixing of the transmitter quadrature-phase baseband signal and a second phase of the separation frequency signal; summing the receiver in-phase baseband signal with one of the first echo copy or the second echo copy to generate a modified receiver in-phase baseband signal; summing the receiver quadrature-phase baseband signal with the second echo copy or the first echo copy to generate a modified receiver quadrature-phase baseband signal; slicing at least one of the modified receiver in-phase baseband signal or the modified receiver quadrature-phase baseband signal to generate ones and zeros; assessing effectiveness of echo cancellation by analysis of run lengths of ones or zeros; delaying at least one signal of a first group or a second group, wherein the first group comprises at least one phase from the Rx LO signal used for upconversion, and wherein the second group comprises the first echo copy and the second echo copy; scaling the first echo copy signal and the second echo copy signal; and adjusting delaying and scaling based at least partly on the assessment of echo cancellation by analysis of run lengths such that the modified receiver in-phase baseband signal and the modified receiver quadrature-phase baseband signal have at least partially canceled echo.