P.S. Pokrovsky – Ph.D.(Eng.), Associate Professor, Department «Radio Control and Communications»,  Ryazan State Radio Engineering University E-mail: paulps@list.ru

The processing of radio signals with controlled coupling between quadrature components (RСCQC) using one of the classification modulation algorithm is analyzed. The synthesis of RСCQC is done to maximize the entropy of this classification algorithm decisions. The first synthesized RСCQC is rational to use for increasing the structural hiding of radio channel with restrictions on the spectral and energy characteristics. The second synthesized RСCQC provides the maximum of ambiguity for the considered classification modulation algorithm, but it is inferior to known radio signals with bandwidth-efficient modulations of 0.8 dB for noise immunity and 8% for spectral efficiency.

In the article radio-signals with controlled communication between the in-phase and quadrature components (RSCCQC) are considered. The mathematical apparatus of these signals allows to combine in software-tunable devices forming and processing units for radio signals with such bandwidth-efficient modulations as Gaussian minimum shift keying (GMSK), K. Feher-patented quadrature phase shift keying (FQPSK), trellis-coded offset quadrature phase shift keying (T-OQPSK), etc. For such RSCCQC, decisions generated by one of known modulation type recognition algorithms are analyzed. At that three series of known RSCCQC are considered which include both sets to form signals with GMSK and FQPSK, as well as a set of the signals synthesized by the combined criterion «occupied bandwidth – crest factor».

It is shown that the considered recognition algorithm with probability more than 50% distinguishes different RSCCQC inside these series as both radio signals with frequency modulations and ones with phase modulations. To define signals that are stable to recognize modulation type by the considered algorithm, an additional analysis of the RSCCQC set was made. The entropy of decision obtained by the recognition algorithm was used as quality index in this analysis. As a result, several local maxima of entropy was detected on the RSCCQC set. For the most pronounced optima, five RSCCQC were synthesized using methods nonlinear programming. These RSCCQC are characterized by an ambiguity of modulation type recognition corresponding to an entropy of 1.5 bits.

Subsequent analysis allowed to select two signals which are reasonable to use in prospective communication systems. The first RSCCQC is comparable with known bandwidth-efficient signals in terms of the main spectral and energy features. This RSCCQC provides the entropy of decision generated by considered the recognition algorithm at the level of 1.58 bits. The second RSCCQC is inferior to known radio signals in general parameters (of 0.8 dB for noise immunity and 8% for occupied bandwidth), but provides the ambiguity maximum of modulation type decisions (entropy of more than 1.95 bits) within the analyzed set.

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