Joint Compensation of Frequency-Selective I/Q Imbalance and CFO in OFDM-Based WLAN

Recently, based on modified periodic pilot (MPP), a compensation scheme for carrier frequency offset (CFO) and I/Q imbalances in direct-conversion wireless receivers, has been proposed. However, it cannot be applied to IEEE 802.11 a WLAN directly, where only periodic pilot (PP) exists. In this paper, the impact of PP on the MPP-based scheme is studied. The results indicate that PP causes fatal degradation of performance, by inducing sign ambiguity in CFO estimation and invalidating the compensation of I/Q imbalances in the absence of CFO. Then, an efficient compensation scheme for the IEEE 802.11 a WLAN is proposed. In the proposed scheme, the CFO estimation is enhanced by a CFO sign detection and an autocorrelation-based estimator. Also, a novel I/Q imbalances compensation algorithm robust to the CFO value is proposed. Taking full advantage of the 802.11 a preamble, the proposed scheme is competent for various scenario of CFO and I/Q imbalances, which is confirmed by simulations.