Perekrestov I. Demodulation in radio channels with variable parameters based on open-loop systems of phase synchronization

Object - the process of digital signals demodulation in radio channels with variable parameters. Purpose - solution the task of open-loop phase synchronization based on the maximum likelihood method in channel with time-varying parameters for optimum demodulation. Analysis methods: a mathematical analysis for substantiation of open-loop phase synchronization correspondence to maximum likelihood method of estimation, mathematical analysis with usage of statistical radio engineering methods during research for developed synchronization method, computer simulation in the research process, and the least square method approximation at development of estimation algorithms of radio channels statistical characteristics. Theoretical and practical results: To solve the task in the processing of high-frequency region the method of open-loop phase synchronization was developed and analyzed in detail, including reasonable the realization of the maximum likelihood estimation. In the processing of low-frequency region the rules of optimal adaptive estimation of time-varying parameters in the multi-path radio channel were de-fined. Correlation properties of the radio channel parameters for different models in frequency and time domains and the law of probability distribution of frequency shifts were studied. The known expression of nonorthogonality noise power estimation was refined. Minimum error probability of recovered binary digital signal was used as an objective criterion for the quality of synchro-nization. Scientific novelty: 1. For the first time was revealed that the frequency shifts in multi-path radio channel for moving subscriber have scalable Student distribution. Using founded distribution law of frequency shifts and investigations of correlation properties of frequency shifts, the expression of nonorthogonality noise power estimation was refined. 2. The theory of open-loop phase synchronization was further developed - new method of synchronization at high-frequency processing was substantiated. The correspond schemes in terms of influence of self-distortions and noise on the synchronization accuracy and noise immunity were analyzed. 3. For the first time the new method of definition of time-frequency coherence area was proposed. This method takes into account that at the signal processing in conventional coherence area the additive noise and linear channel processing distortions affects on estimation accuracy. Revealed - the size of coherence area is the function of signal-to- noise ratio. 4. For multi-path radio channel models that are recommended by ITU for third-generation transmission systems, the analytical expression of correlation function of amplitude fading in frequency domain was refined -coefficients that specify the rms of channel delay spread was founded. According to this, for the first time the expression for definition of channel delay spread by estimation of pilot subcarrier in one OFDM symbol was developed. 5. Improved method for determining of Doppler spectrum spread, the corresponding analytical expression is obtained. The results introduced in the following organizations: Odessa National Academy of Telecommunications named after A. S. Popov, proposed for use in education process and for graduate students' scientific research.