Adaptive IQ imbalance correction for OFDM systems with frequency and timing offsets

Direct conversion (from RF to complex I and Q baseband in one mixing step) architectures are increasingly popular as they enable lower implementation costs. The resulting frequency dependent amplitude and phase imbalance between the I and Q conversion rails can cause significant performance degradations to complex modulation techniques such as 64-QAM and above typically used for high data rate transmission. Conventionally, this IQ imbalance is only corrected at the receiver at power up while the imbalance at the remote transmitter is assumed to be pre-corrected. However, aging, manufacturability, and temperature variations can be difficult to calibrate and can result in performance degradation (e.g., range reduction, etc.). Future ad hoc networks will also require imbalance correction per packet as they might come from many different transmitters. in this paper, we propose an adaptive scheme in the receiver to correct the IQ imbalances at the remote transmitter as well as the receiver. The proposed scheme, as it jointly corrects remote transmitter and local receiver I imbalances in the presence of frequency and timing rate offsets, is therefore more robust than the earlier results.