V.I. Simongauz – Ph.D.(Eng.), Associate Professor,
Department 402, Moscow Aviation Institute (National Research University) E-mail: simongauz@rambler.ru
The article deals with the task of constructing algorithms for estimating the frequency of the carrier oscillation at the stage of entering into the connection. When processing a radio signal with quadrature phase modulation (QPSK), the nonlinear transformation of digital samples of the complex envelope – raising to the fourth power – is used to eliminate the influence of the modulating function. Frequency estimation is based on the construction of a discrete spectrum in a given range of frequency uncertainty using the FFT algorithm. The calculation of the probability of an anomalous error in estimating the carrier frequency is given and the energy characteristics that provide the necessary noise immunity are found. When the energy potential characteristic of the radio space communication, it is advisable at the stage of entering the connection to carry out processing of the unmodulated carrier, and to use the results of the frequency evaluation as initial data in the tracking phase synchronization algorithm for radio processing with modulation. Processing the unmodulated carrier provides a significant energy gain in noise immunity compared to processing a modulated radio signal.
To quickly enter the phase synchronization loop tracking mode, it is necessary to obtain an estimate of the carrier frequency. This problem is solved at the stage of entry into the relationship. When receiving a suppressed carrier radio signal, a non-linear transformation of the input process should be performed to eliminate the influence of the modulating function. For a radio signal with quadrature phase modulation (QPSK), this transformation is reduced to the construction of the input process in the fourth degree. The processing of the complex envelope is considered. The spectral characteristics of the process after nonlinear transformation are obtained. In digital processing, a discrete sampling spectrum is built in a given frequency uncertainty range using an FFT algorithm. As an estimate of the frequency, the frequency of the discrete spectrum component with the maximum level is taken. The calculation of the probability of an «anomalous» error in the evaluation of the frequency, depending on the energy characteristics of the radio link. When the energy potential characteristic of the radio space communication, it is advisable at the stage of entering the connection to carry out processing of the unmodulated carrier, and to use the results of the frequency evaluation as initial data in the tracking phase synchronization algorithm for radio processing with modulation. Processing the unmodulated carrier provides a significant energy gain in noise immunity compared to the processing of a modulated radio signal.
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