Low-Complexity Estimation of Carrier and Imbalance Parameters 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. But the price to pay is an additional impairment introduced by IQ mismatch and DC offset, which might be compensated by appropriately designed DSP algorithms. In this context, recovery of carrier and imbalance parameters has been investigated in many publications available from the open literature. For the current paper, however, we first derive the Cramer-Rao lower bound (CRLB) as the theoretical limit of the jitter variance for joint estimation of carrier frequency/phase, IQ gain/phase imbalance, and DC offset; to this end, the correlation of the noise components – in numerous contributions tacitly neglected – is explicitly taken into account. In the sequel, by means of several simplification steps, we present an approximate closed-form solution for the recovery of carrier and imbalance parameters, whose jitter performance is verified to be close to the CRLB, underlining this way the efficiency of the proposed method.