Recovery of an information sequence with the help of the extended Kalman filter included in the variable-symbol-frequency modem

The digital modem structure with the chaotically varying symbol frequency is proposed. Two approaches to symbol-frequency recovery, which are based on chaotic sequence synchronization and an extended Kalman filter, are discussed. It is found that the spectrum of an output signal with the chaotically varying symbol frequency contains substantially decreased (by 12–15 dB) unwanted components. Energy curves making it possible to estimate the dependence between the error probability and the degree of variation in symbol-interval duration are constructed. An experimental model of the modem built around a Spartan-3A DSP field programmable gate array is proposed.