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 intercarrier 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.
"However, no antenna diversity was considered in  . The scheme in  considers MIMO OFDM with high mobility and applies comb-type pilots , which is not optimal for indoor scenario with block fading channels. Moreover, the efficient self calibration scheme in  is only applicable for MIMO OFDM systems with symmetrical TX and RX structures. "
[Show abstract][Hide abstract] ABSTRACT: MIMO OFDM is a very promising technique for high-speed wireless transmission. By applying the Direct Conversion Architecture (DCA), low-cost, low-power and fully integrated implementation of such systems is enabled. However, the performance of DCA may be seriously limited by I/Q-imbalance, which shows frequency selectivity in broadband systems. In this paper, we consider an indoor scenario and present effective preamble based joint compensation of the MIMO wireless channels (block fading) and the TX- and RX-frequency-selective I/Q-imbalance. Two low overhead preambles are proposed, which are constructed in time- and frequency domain, respectively. Both of them have their own advantages. Compared to the literature, our paper considers more practical issues and shows how to choose the adequate preamble design according to system parameters to achieve the best performance with relatively low computational complexity. Effectiveness of the proposed schemes is verified by numerical simulation.
2010 IEEE Wireless Communications and Networking Conference, WCNC 2010, Proceedings, Sydney, Australia, 18-21 April 2010; 01/2010
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