Improved Demodulation of Sampled FM Signals in High Noise

Simulation results are presented which are very convincing in favor of FM demodulators driven by in-phase and quadraturephase signals. Application of the extended Kalman filtering algorithms to the appropriate signal model directly yields demodulators in which the error covariance equations are uncoupled from the state estimate equations. These demodulators perform a little better than others derived using different nonlinear filtering techniques and the necessary approximations to achieve "decoupling." More significantly, these demodulators using in-phase and quadrature-phase sampled signals are readily augmented to achieve demodulation with delay by the application of fixed-lag smoothing algorithms. Simulations highlight the attractive trade-offs between demodulation complexity and performance results for this class of demodulator.