Compensation of transmitter IQ imbalance for OFDM systems

Zero-IF transceivers are gaining interest because of their potential to enable low-cost OFDM terminals. However, the zero-IF architecture introduces IQ imbalance which may have a huge impact on the performance. Rather than increasing component cost to decrease the IQ imbalance, an alternative is to tolerate the IQ imbalance and compensate it digitally. Current solutions require extra analog hardware at the transmitter. We analyze transmit IQ imbalance estimation and propose a low-cost, highly effective estimation scheme, which is fully digital and located at the receiver. Performance analysis shows that this scheme can provide up to 4 dB gain while meeting the IEEE 802.11a constellation accuracy specification and more if larger IQ imbalance is present in the transmitter. It therefore enables the design of low-cost, low-complexity OFDM modems.