Joint estimation of I/Q imbalance and channel response for MIMO OFDM system

In this paper, we study joint estimation of in-phase and quadrature-phase (I/Q) imbalance and channel response for multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems using training sequence. A new class of optimal sequences, called circularly-shift orthogonal sequences, are introduced for estimating the MIMO channels. By using the newly proposed sequences, the channel coefficients can be obtained by multiplying the received vectors with an M × M unitary circulant matrix, which can be computed efficiently using FFT. Then, we develop a new method for jointly estimating the MIMO channel responses and I/Q imbalance. The proposed time-domain method needs only one OFDM training block. Simulation results show that the proposed method can accurately estimate both the I/Q imbalance and MIMO channel response.