Efficient Joint Estimation Methods of Channel and IQ Imbalance for MIMO-OFDM Systems

In Orthogonal Frequency Division Multiplexing (OFDM) systems, a general method to estimate frequency-selective in-phase and quadrature-phase (IQ) imbalance is to transmit pilot signal over two symbols with half the subcarriers nulled to avoid inter-carrier interference (ICI). In Multiple-Input Multiple-Output (MIMO)-OFDM systems, the number of pilot symbols required to mitigate interference increases in proportion to the number of transmit antennas. In this case, the total transmission rate is also degraded. To reduce this problem, we propose an efficient joint estimation method of channel and IQ imbalance using a novel pilot signal with multiple impulses in the time domain. Thanks to the pilot design with densely arranged impulse responses, we can identify the IQ imbalance and obtain the accurate channel response with a small number of pilot symbols.