PROBLEM TO BE SOLVED: To simultaneously estimate I/Q gain and phase mismatches of both transmit and receive paths of an OFDM FDD transceiver.SOLUTION: An up-converted RF signal is generated when the transmit path performs IQ modulation on a reference signal having a single sideband tone. The up-converted RF signal is sent via a loop-back path to the receive path. A down-converted evaluation signal is generated when the receive path performs IQ demodulation on the up-converted RF signal. A single evaluation signal is used to determine the transmit path gain and phase mismatches as well as the receive path gain and phase mismatches. The four I/Q mismatches are estimated without using large hardware not used in regular transmission of data signals. The I/Q mismatches in the data signals are corrected by pre-processing the up-converted RF signals and post-processing the down-converted RF signals by summing attenuated components of the in-phase and quadrature-phase signals.