Preamble design for joint estimation of CFO and I/Q imbalance for direct conversion OFDM system

This paper proposes a preamble structure for joint estimation of carrier frequency offset (CFO) and I/Q imbalance. Because existing methods cannot guarantee correct solutions within all range of CFOs, we derive two constraints of phase rotations applied to repetition patterns. By using the preamble based on the presented constraints, CFO is optimally estimated, and I/Q imbalance estimation is possible in all ranges of CFO with low complexity. Numerical results verify the importance and necessity of these constraints for joint estimation.