Analysis of space-frequency coded OFDM with I/Q imbalance

Imperfections in analog circuits are serious obstacles to the realization of high data rate transmission for multiple-input multiple- output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems. An I/Q imbalance is one of such imperfections affecting the up- and down-conversions of quadrature modulators and demodulators in RF front-ends of transceivers. In this paper, we consider MIMO OFDM with the receiver I/Q imbalance and propose a novel space-frequency code (SFC) over mirror subcarriers based on the Alamouti scheme. The suggested scheme compensates for the I/Q imbalance efficiently without any additional signal processing. We analyse the symbol-error rate (SER) performance of the proposed scheme under two linear receiver algorithms and different fading conditions, and compare it with the SER of the SFC scheme across the adjacent subcarriers. A modification of the latter scheme is proposed and analyzed too. We present recommendations about using the above SFC schemes under different fading scenarios.