Frequency Offset Estimation Scheme in the Presence of Time-Varying DC Offset and IQ Imbalance for OFDM Direct Conversion Receivers

In WLAN systems, direct conversion architecture has been implemented. Though this architecture reduces the cost and power consumption, it may suffer from DC offset, frequency offset, and IQ imbalance. This paper presents a frequency offset estimation scheme for OFDM direct conversion receivers. In this paper, a frequency offset estimation scheme in the presence of time-varying DC offset and IQ imbalance is proposed. The novelty of this scheme is in its usage of a differential filter to reduce DC offset. Evaluation of the presented estimation scheme was carried out on an OFDM communication system designed to the specifications of the IEEE 802.11a/g standard for WLANs. Numerical results through computer simulation show that the proposed frequency offset estimation scheme works well even with large DC offset and IQ imbalance.