Direct-conversion radio architecture is a low-cost, small-size design for the analog front-end subsystem in a wireless communication transceiver. This architecture, however, induces radio impairments such as I-Q imbalance and dc offset that, along with frequency offset, incur severe degradation in communication performance. This paper aims to improve the performance of estimation and compensation for cascaded transmitter and receiver radio impairments in the MIMO-OFDM (multiple-input, multiple-output orthogonal frequency-division multiplexing) systems. First, a novel two-stage compensation scheme is proposed which is applicable to a general form of MIMO operations with any number of transmit and receive antennas. Second, with a periodic training, an improved low-complexity joint estimation and compensation algorithm for radio impairments is proposed. Numerical results show the superiority of proposed method over the existing ones in bit error rate (BER) performance and training overhead.

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Direct-conversion radio architecture is a low-cost, small-size design for the analog front-end subsystem in a wireless communication transceiver. This architecture, however, induces radio impairments such as I-Q imbalance and dc offset that incur severe degradation in communication performance. In this paper, a new time-domain method is proposed to self-calibrate simultaneously the transmitter and receiver impairments without a dedicated analog circuit in the feedback loop. Thanks to the timedomain approach, the method is applicable to all types of systems and is able to calibrate jointly the frequency-independent I-Q imbalance, frequency-dependent I-Q imbalance, and dc offset. In addition, training sequence design is investigated to optimize the performance of calibration. Analytical and simulation results confirm the effectiveness of the proposed method.

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