The invention is used in an OFDM communication system. The apparatus comprises: a frequency mixing module for making frequency mixing for a radio signal in order to generate an in-phase analog signaland a quadrature phase analog signal; an in-phase/quadrature phase unbalanced parameter estimation unit, coupled to the frequency mixing module, for use in estimating a gain compensation value and a phase compensation value; and a signal compensating unit, coupled to the in-phase/quadrature phase unbalanced parameter estimation unit, for use in using the gain compensating value to compensate the gain unbalance and using the phase compensating value to compensate the phase unbalance.