A key task in the way of creating new digital radio communication systems is the development of more efficient and more resistant to unfavorable reception conditions of digital synchronization methods. At the same time, the main role is played by systems using phase manipulation of the signal, which are the most common and, accordingly, the most practically important.
A hybrid method of signal demodulation is proposed, which combines algorithms for direct estimation of signal parameters (feedforward) with further synchronization of parameters according to schemes with feedback. A comparative simulation of well-known traditional demodulation methods and the hybrid method is performed on the example of signals with phase manipulation. The obtained results confirm that in conditions of rapid changes in signal parameters, the hybrid algorithm provides the minimum value of the bit error depending on the SNR in comparison with traditional methods, which are based separately on feedback or feedforward synchronization schemes. The proposed hybrid combination of feedback and feedforward algorithms made it possible to apply feedback algorithms to signals with a packet data transmission mode. The considered approach to synchronization can also be used for signals with other types of phase manipulation.
Modern frame synchronization algorithms for the DVB-S2 satellite communication standard have been studied. The use of differential methods makes it possible to abandon the initial estimate of the carrier frequency offset and speed up the registration of the communication modem. An algorithm with an adaptive threshold is proposed, which is based on the use of differential signal correlation. A feature of the presented method is that with a change in the level of the input signal, the threshold for making a decision also changes adaptively, which allows to abandon the system of automatic power regulation at this stage of signal processing. Comparative modeling of the proposed method of frame synchronization with known methods based on the calculation of differential correlation was carried out, the results of the obtained characteristics of the probability of omission from the signal/noise ratio showed the advantage of the proposed algorithm over known methods. Ways of practical implementation of this algorithm on the FPGA element base are also considered.
A new approach to signal demodulation based on particle filtering methods is introduced. The main principle of corpuscular filtering is the approximation of the distribution of unknown parameters using a discrete set of particles and their associated weighting factors. A model of the state space of the observation signal is formulated, taking into account the dynamics of updating channel parameters. A comparative analysis with well-known demodulation methods was carried out on the example of signals with phase manipulation. It is shown that with a sufficient number of corpuscles, the demodulation efficiency, namely ensuring the minimum bit error (BER), can be improved by applying corpuscular filtering methods at low signal-to-noise ratios against a background of non-Gaussian noise.
A method of detecting the version of the DVB-S2/S2X standard has been developed using the proposed methods of synchronization and decoding of service information of the physical level. The detector consists of frame synchronization systems, a demodulator and a PLSCODE field decoder. The formulas for calculating the PLSCODE bit field and decoding the service information, respectively, are proposed for the DVB-S2 and DVB-S2X broadband notification standards. The presented detector allows to determine to which revision the transmitted signal belongs and to determine the parameters of the frame. A software model of the described method has been developed. Experimental calculations of the ROC curve and the miss detection probability from the signal/noise ratio were performed. The obtained simulation results show the high efficiency of the proposed detection method even with negative signal to noise ratios.
Also, the paper proposes a method of identifying signals that are transmitted using Carrier-to-Carrier technology using QPSK modulation. The method is based on the calculation of fourth-order cumulants to detect changes in the shape of the signal constellation, which are characteristic of Carrier-in-Carrier signals. According to the receiver operating characteristic (ROC) methodology, a threshold value for the decision rule is found. It was established that the proposed method provides correct detection of the sum of QPSK signals for a wide range of signal-to-noise ratios, different amplitudes of signals from the sum, and also for different bandwidths of mixed signals. The obtained results indicate the high efficiency of the proposed detection method. The advantage of the proposed detection method over the "radius" method is also shown.
