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

Abstract

Abstract-Direct-conversion Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from transmit and receive analog processing impairments such as Inphase/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 frequencydependent 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.

Performance and Compensation of I/Q Imbalance in Differential STBC-OFDM

“…However, by examining Eqs. (17) and (18), we find that the differential relationship no longer holds in the presence of RX-IQI even without noise,…”

“…The system parameters are similar to [17]. The transmitter sends 8-PSK modulated symbols over a bandwidth of 5MHz and the operating frequency is 2.5GHz.…”

“…The frequency-domain RX-IQI-distorted received signals in Eqs. (17) and (18) can be expressed in the widely-linear equivalent form shown in Eqs. (45) and (46) below where S k+1 (n) = S k (n)U k+1 (n).…”