Compensation of IQ imbalance in OFDM systems

Today a lot of attention is spent on developing inexpensive OFDM receivers. Especially, zero-IF receivers are very appealing, because they avoid costly IF filters. However, this implies IQ demodulation at RF, which therefore cannot be done digitally and thus introduces IQ mismatch. Unfortunately, OFDM is very sensitive to receiver IQ imbalance. Therefore, we developed a new compensation scheme to combat the IQ imbalance at baseband. In this paper, we describe the algorithm and present the performance results. Our compensation scheme eliminates the IQ imbalance almost perfectly. This leads to tremendous improvements, especially in multi-path channels (up to 10 dB performance gain), and enables lowcost zero-IF receivers.