Joint compensation of IQ imbalance and frequency offset in OFDM systems

Zero-IF receivers are gaining interest because they enable low-cost WLAN OFDM terminals. However, zero-IF receivers introduce IQ imbalance which may have a huge impact on 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 converge too slowly for bursty WLAN communication. Moreover, the tremendous impact of a frequency offset on the IQ estimation/compensation problem is not considered. We analyze joint IQ-CFO estimation/compensation and propose a low-cost, highly effective compensation scheme. For large IQ imbalance (ε=10%, Δφ=10°) and large frequency offset, our solution results in an average remaining degradation below 0.5 dB compared to the reference case without IQ imbalance or frequency offset. It therefore enables the design of low-cost, low-complexity WLAN OFDM receivers.