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Architectures for radio receivers are driven by market demands for low-cost and low power solutions for wireless communications. Toward that end, the implementation of direct conversion receivers which convert the radio frequency (RF) signal directly to baseband has been the subject of active research. Gain and phase imbalances between in-phase and quadrature paths, however, are more pronounced in such designs compared to classical heterodyne architectures. If left uncompensated, even small amounts of IQ mismatch could render the communication system ineffective. We propose a novel algorithm for estimation and compensation of gain and phase mismatch values in the receiver mixer for an OFDM communication system. Relations are derived for the estimation of the relevant parameters and the statistical properties of the estimates are investigated. The calibration procedure is tested on an OFDM system designed based on the IEEE 802.11a standard for wireless local area networks.