Transaction on IoT and Cloud Computing 2(1) 13-56 2014 Preamble Assisted Estimation and Compensation of Frequency Selective I/Q Imbalance in MIMO OFDM Systems

MIMO OFDM is a key technique for achieving high capacity in future wireless communi-cation systems. The desired low-cost, low-power and fully integrated implementation of MIMO OFDM systems leads to the application of direct (up/down) conversion architec-ture, whose performance can be seriously limited by the RF impairment I/Q imbalance. Thus, the compensation of I/Q imbalance is a crucial issue in the implementation of MI-MO OFDM systems, which requires reliable parameter estimation. In this paper, we first present an overview of I/Q-imbalance compensation in MIMO OFDM systems. After-wards, we propose three preamble assisted schemes for efficient joint estimation of the MIMO channel and frequency-selective transmiter (Tx) and receiver (Rx) I/Q imbalance. Correspondingly, three advanced preamble designs are presented, incl. a preamble based on Time Domain Separation (TDS), a preamble based on Frequency Domain Separation (FDS) and a multi-functional preamble. All preamble designs allow low overhead and low Crest-Factor (CF). Based on these preamble designs, low complexity estimators are developed, which can achieve performance close to the Cramer-Rao Lower Bound (CRL-B). Numerical simulation results and complexity analysis have verified the advantages of the proposed schemes over the existing schemes. Finally, we discuss how to select the most appropriate scheme- out of the proposed three- by considering a tradeoff between performance, complexity and overhead