Co-channel signal separation using coupled digital phase-locked loops




Hedstrom, Brad Allen

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Side effects of frequency reuse are discussed, particularly co-channel interference in scalar measurement FM systems. Continuous and discrete time state-space models for multiple source angle modulated communications environments are developed and coupled digital phase-locked loop (CDPLL) estimator structures are derived based on the Extended Kalman Filter (EKF). Separability of two sources is investigated by examination of state observability and by simulations of the derived estimators. The relationship between the EKF and the CDPLL is presented and their linear and nonlinear behavior discussed. Acquisition and tracking characteristics are simulated and results presented. The new estimator is compared to related efforts found in the literature. The effects of time-varying signal multiplicity is briefly treated. An example of polarization diversity for frequency reuse (vector measurement) is also presented and is shown to be adequately modeled by the derived communications model.



Signal processing, Digital computer simulation