Preamble Design for an Efficient I/Q Imbalance Compensation in OFDM Direct-Conversion Receivers

The growing number of different mobile communications standards calls for inexpensive and highly flexible receiver architectures supporting these standards. The direct-conversion receiver is a very attractive candidate for reaching this goal. However, unavoidable imbalances between the Iand the Q-branch of the I/Q demodulator lead to a significant performance degradation at the reception of OFDM signals. A digital estimation and compensation of the unwanted effects of the I/Q imbalance is possible. In this paper we consider an I/Q imbalance parameter estimation based on the preamble of OFDM systems. General constraints for the design of the preamble are derived, which enable a robust and computationally efficient I/Q imbalance compensation. Design examples are presented and evaluated.