Digital baseband compensation of joint TX/RX frequency-dependent I/Q imbalance in mobile MIMO-OFDM transceivers

Direct-conversion Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from transmit and receive analog processing impairments such as In-phase/ Quadrature (I/Q) imbalance causing Inter-Carrier Interference (ICI) between the sub-carriers. Another source of performance-limiting ICI, but with a different nature, in OFDM systems is Doppler spread due to mobility. Unlike previous work which considered these two problems separately, we develop a generalized analytical framework to characterize, estimate and jointly mitigate ICI due to both I/Q imbalance and high mobility. Based on our general model, we exploit the special ICI structure to design efficient channel and I/Q imbalance parameter estimation and digital baseband compensation schemes for joint transmit/receive frequency-independent and frequency-dependent I/Q imbalance under high-mobility conditions. Moreover, we extend the model, compensation and channel estimation methods to the Multiple Input Multiple Output (MIMO) case, Spatial Multiplexing (SM) in particular.