Noncircular Measurement and Mitigation of I/Q Imbalance for OFDM-Based OFDM WLAN Transmitters
Abstract: In future high-speed speed communication networks, the in in-phase/quadrature phase/quadrature (I/Q) imbalance mitigation and oscillator drift compensation is a key issue in the design of orthogonal frequency division multiplexing (OFDM) (OFDM)-based based wireless LAN (WLAN) transmitters. To this end, we propose a two-stage two stage I/Q imbalance measurement method, where ere by virtue of the WLAN standard standard-compliant compliant training sequences, a coarse I/Q imbalance estimation is initially performed jointly with channel equalization. This makes it possible to decouple the effects of frequency-selective frequency channels from the exact ampli amplitude tude and phase imbalances induced by the local oscillator. Next, the so recovered symbols in DATA field of standardized OFDM systems, such as the IEEE 802.11ac, are recalibrated using a decision-directed decision scheme; this facilitates least squares-based squares fine I/Q Q imbalance estimation. For rigor, augmented complex statistics is employed to account for the effects of data noncircularity and widely linear natures of communication channels. Computer simulations and real world experiments based on the IEEE 802.11ac compliant co signals demonstrate the high accuracy of the proposed technique for OFDMOFDM based WLAN transmitters.