On Estimation of Intermodulated Frequencies for Sinusoidal Signals With Unknown Fundamental Frequencies

In this correspondence, the problem of estimating the intermodulated frequencies of sinusoidal signals with unknown fundamental frequencies is investigated. It is shown that by formulating the intermodulation structure as a constraint in the estimation of these frequencies, a smaller Cramer-Rao lower bound (CRI,B) can be obtained, that is, a more accurate estimate of these frequencies can be obtained. The steps in the proposed estimation procedure are i) obtaining initial estimate of the frequencies using existing methods, ii) establishing the intermodulation structure from the initial estimate of the frequencies, and iii) refining the initial estimate using the intermodulation structure. The implementation and performance of the proposed estimation procedure is demonstrated by a simulation example.