Joint compensation of IQ imbalance and frequency offset in OFDM systems

Zero-IF receivers are gaining interest because of their potential to enable low-cost OFDM terminals. However, zero-IF receivers introduce IQ imbalance which may have a huge impact on the performance. Rather than increasing design time or component cost to decrease the IQ unbalance, an alternative is to tolerate the IQ imbalance and compensate it digitally. Current solutions require extra analog hardware or converge too slowly for bursty communication. Moreover, the tremendous impact of a frequency offset on the IQ estimation/compensation problem is not considered. In this paper, we analyze the joint IQ imbalance-frequency offset estimation and propose a low-cost, highly effective, all-digital compensation scheme. For large IQ imbalance (∈ = 10%, Δφ = 10°) and large frequency offsets, our solution results in an average implementation loss below 0.5 dB. It therefore enables the design of low-cost, low-complexity OFDM receivers.