Digital baseband compensation of joint TX/RX frequency-dependent I/Q imbalance in mobile MIMO-OFDM transceivers
ABSTRACT 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.
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ABSTRACT: In-phase and quadrature-phase (I/Q) imbalance is a major performance-limiting impairment for direct- conversion orthogonal frequency division multiplexing (OFDM) transceivers. I/Q imbalance degrades the signal-to-noise-ratio in an OFDM system by causing inter-channel-interference (ICI) between image subcarriers. Doppler spread due to mobility also causes ICI but mainly between adjacent subcarriers. In this work, we investigate the combined effects of mobility and I/Q imbalance in a multiple-input-multiple-output-OFDM system with the alamouti space-frequency block-coding scheme and design an effective compensation technique. Furthermore, we propose a novel pilot allocation and channel estimation scheme, and exploit the problem structure to reduce complexity.Global Telecommunications Conference, 2008. IEEE GLOBECOM 2008. IEEE; 01/2009
Conference Paper: Compensation of IQ imbalance in OFDM systems[Show abstract] [Hide abstract]
ABSTRACT: Today a lot of attention is spent on developing inexpensive OFDM receivers. Especially, zero-IF receivers are very appealing, because they avoid costly IF filters. However, this implies IQ demodulation at RF, which therefore cannot be done digitally and thus introduces IQ mismatch. Unfortunately, OFDM is very sensitive to receiver IQ imbalance. Therefore, we developed a new compensation scheme to combat the IQ imbalance at baseband. In this paper, we describe the algorithm and represent the performance results. Our compensation scheme eliminates the IQ imbalance almost perfect. This leads to tremendous improvements, especially in multi-path channels (up to 10 dB performance gain), and enables low-cost zero-IF receivers.Communications, 2003. ICC '03. IEEE International Conference on; 06/2003
Conference Paper: Digital Baseband Compensation of I/Q Imbalance in Mobile OFDM[Show abstract] [Hide abstract]
ABSTRACT: I/Q imbalance and high mobility in OFDM systems result in performance-limiting intercarrier interference (ICI). However, the nature of ICI due to each of them is quite different. Unlike previous works which considered these two impairments separately, we develop a unified mathematical framework to characterize and mitigate ICI when both impairments are present. In addition, we exploit the special ICI structure to design efficient OFDM channel estimation and digital baseband compensation schemes for I/Q imbalance under high-mobility conditions.Wireless Communications and Networking Conference, 2008. WCNC 2008. IEEE; 01/2008