Abstract
Multiple-input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) scheme has been considered as the most promising physical-layer architecture for the future wireless systems to provide high-speed communications. However, the performance of the MIMO-OFDM system may be degraded by in-phase/quadrature-phase (I/Q) imbalances caused by component imperfections in the analog front-ends of the transceivers. I/Q imbalances result in inter-carrier interference (ICI) in OFDM systems and cause inaccurate estimate of the channel state information (CSI), which is essential for diversity combining at the MIMO receiver. In this paper, we propose a novel approach to analyzing a MIMO-OFDM wireless communication system with I/Q imbalances over multi-path fading channels. A virtual channel is proposed as the combination of multi-path fading channel effects and I/Q imbalances at the transmitter and receiver. Based on this new approach, the effects of the channel and I/Q imbalances can be jointly estimated, and the influence of channel estimation error due to I/Q imbalances can be greatly reduced. An optimal minimal mean square error (MMSE) estimator and a low-complexity least square (LS) estimator are employed to estimate the joint coefficients of the virtual channel, which are then used to equalize the distorted signals. System performance is theoretically analyzed and verified by simulation experiments under different system configurations. The results show that the proposed method can significantly improve system performance that is close to the ideal case in which I/Q are balanced and the channel state information is known at the receiver.
Highlights
Due to the rapid growth of broadband wireless applications, the generation of wireless communication systems poses major challenges for efficient exploitation of the available spectral resources
The results show that the proposed method can significantly improve system performance that is close to the ideal case in which I/Q are balanced and the channel state information is known at the receiver
We introduce a new virtual channel concept to analyze the I/Q imbalances in a Multiple-input multiple-output (MIMO)-orthogonal frequency-division multiplexing (OFDM) wireless communication system over multi-path fading channels
Summary
Due to the rapid growth of broadband wireless applications, the generation of wireless communication systems poses major challenges for efficient exploitation of the available spectral resources. In [29], the input-output relation of a MIMO-OFDM system with frequency-independent I/Q imbalances at the receiver is derived Based on this result, an adaptive method is introduced to compensate for the received data. In [31], the effect of frequency-dependent I/Q imbalances on MIMO-OFDM system is studied, using a pilot-based compensation scheme In both studies, the received signals are diversity combined using inaccurate channel state information (CSI) estimated under I/Q imbalances, leading to system performance degradation. A novel approach is proposed to analyze MIMO-OFDM wireless communication systems with I/Q imbalances over multi-path fading channels. A frequency-dependent I/Q imbalances model and an Alamouti scheme-based MIMO-OFDM model with transmitter and receiver I/Q imbalances are described.
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