CRLB and low-complex algorithm for joint estimation of carrier frequency/phase and IQ imbalance in direct-conversion receivers

Due to aggressive goals for future communication systems, direct-conversion receivers are an attractive option in terms of compactness and power dissipation. However, the price to pay is an additional impairment introduced by IQ imbalance, which might be compensated by appropriately designed DSP algorithms. In this context, joint recovery of carrier phase and IQ gain/phase imbalance has been presented in some recent publications. Since correlation of the noise components has been neglected, this issue was explored by the authors in a follow-on paper. In the current contribution, the carrier frequency offset is taken into account as well. Through several simplification steps, an approximate closed-form solution is developed for joint estimation of carrier frequency/phase and IQ gain/phase imbalance, whose jitter performance is close to the Cramer-Rao lower bound (CRLB) as the theoretical limit.