Timing sensitivity analysis of a direct transmitter self-calibration technique

This paper studies a least-square-based (LS-based) self-calibration technique in a direct frequency conversion quadrature modulator. The technique requires the in-phase (I) and quadrature (Q) signals and their associated instantaneous power measurement at the transmitter to calculate the gain/phase/DC-offset coefficients. The time synchronization between the I/Q signals and the power measurement is of importance for accurate gain/phase/DC-offset coefficient estimation. In this paper, we analyze the sensitivity of the LS-based technique to the time synchronization error using higher-order statistics techniques. The analytical result of the coefficient estimation error is derived. Numerical simulations are used to validate this derivation. It is shown that the analytical result is accurate and the self-calibration technique can tolerate a timing error up to 10% of the symbol interval.