V.I. Simongauz – Ph.D.(Eng.), Associate Professor, Moscow Aviation Institute (National Research University)
To quickly enter the phase synchronization loop tracking mode, it is necessary to obtain an estimate of the carrier oscillation frequency. This problem is solved at the stage of entering into communication. When receiving a radio signal with a suppressed carrier, a nonlinear transformation of the input process should be performed to eliminate the influence of the modulating function. For a binary phase modulation (BPSK) radio signal, this conversion is reduced to squaring the input process. The processing of a complex envelope is considered. Spectral characteristics of the process after quadratic transformation are obtained. In digital processing, the construction of a discrete spectrum of samples in a given range of frequency uncertainty using the FFT algorithm is performed. The frequency of the discrete spectrum component with the maximum level is taken as an estimate of the frequency. The calculation of the probability of «abnormal» error in the evaluation of the frequency depending on the energy characteristics of the radio line. With the energy potential characteristic of the radio lines of long-range space communication, it is advisable to process the unmodulated carrier at the stage of entering into the connection, and the results of the frequency assessment are used as initial data in the tracking algorithm of phase synchronization in the processing of the radio signal with modulation. The processing of an unmodulated carrier provides a significant energy gain in noise immunity compared to the processing of a modulated radio signal.
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