Vladimir O. Varlamov

This article presents the results of developing an algorithm for coherent processing of wideband non-binary orthogonal signal-code structures for voice transmission in a decameter radio channel. The structure of a radiogram, including preamble and data symbols, is presented, taking into account message length limitations for real-time voice transmission. An ensemble of orthogonal wideband phase-shift keyed signals is used as signals. The noise-correcting code used is a non-binary low-density parity-check code whose Galois field dimension is matched to the number of signals in the ensemble. Decoding is performed using a belief propagation algorithm, which involves calculating aposteriori probabilities for each possible transmitted symbol, taking into account observations. The article presents analytical expressions for calculating these probabilities, taking into account multipath signal propagation, assuming separation of the paths without their mutual interference, and also taking into account different a priori uncertainties regarding the complex channel transmission coefficients for each path. Three types of a priori information are assumed: fully known complex channel gains, an unknown phase shift of the channel gains, or an unknown phase shift and level of the channel gains. A fourth, widely used, quadratic ray summation option is also considered. In coherent processing, complex channel gains are assumed to be known or measured in some way. This article considers several options for measuring complex channel gains: using a separate measurement channel using the maximum likelihood method and using a Kalman filter. In one version, the Kalman filter operates on data from a separate measurement channel, while in another version, it operates on preamble symbols and on radiogram data symbols with feedback on decisions regarding the data symbols. Using the Waterson model of the ionospheric channel, this article substantiates the autoregressive order of the Kalman filter from the perspective of algorithm complexity and achievable noise immunity. Noise immunity curves are presented for the coherent processing algorithm using the Kalman filter and non-coherent processing algorithms. The corresponding energy gain is estimated.

Increasing the data transfer rate is an urgent task in cellular, high-frequency (HF) and special communication systems. The most common way to increase the data rate is to expand the bandwidth of the transmitted signal, which is often achieved through the use of multitone systems. One such system is the filter bank multicarrier (FBMC). In addition, speed improvements are achieved using multi-input–multi-output (MIMO) systems. In this study, we developed an algorithm for equalizing FBMC signals with offset-QAM modulation (OQAM) with self-interference compensation due to its correlation properties in a MIMO channel with memory. An analytical derivation of the proposed algorithm and an analysis of the computational complexity are given. According to the results of simulation modeling and a comparative analysis of performance in terms of the bit error rate and error vector magnitude with solutions with similar computational complexity, a similar level of performance was shown compared to a more complex parallel multistage algorithm, and a better performance was demonstrated compared to a one-tap algorithm.

This article describes a method to compensate distortions carried by analog analysis filters of a hybrid filter bank. Were obtained expressions describing hybrid filter bank based ADC with addition of compensator. Described processing system was modeled and quantitative measurements of signal distortions were calculated for system with and without compensator. Were shown that insertion of a compensator can significantly improve the characteristics of the system. Methods to increase the computational efficiency of the compensator were described. Dependencies were obtained between the accuracy of compensation and the computational complexity of the compensator.

Currently, there is a tendency to increase the speed of information transmission by increasing used frequency band. However, when switching to broadband signals and operating under conditions of a high level of noise, a wide dynamic range is required when digitizing the received signal. To increase the dynamic range, it is proposed to use a hybrid filter bank, which allows processing the broadband signal with low-speed precision analog-to-digital converters. In this paper, was calculated and simulated a hybrid analysis-synthesis filter bank for the 26.25 MHz-86.25 MHz frequency range. Using matched filters, we estimated the distortion of a linearly frequency-modulated signal during the passage of filter banks without intermediate processing, after upsampling and downsampling intermediate signals from the outputs of analog filters. To reduce phase shifts and time delays arising during signal processing by synthesis filters, compensation delays and phase shifts were introduced, adjusted to distortions carried by the processing system. It was shown that phase correction allows reducing signal distortions. It was also shown that in the case of receiving a mixture of signal and noise, the distortion introduced by the processing system does not significantly affect the signal-to-noise ratio of the output signal.