JUSTIFICATION OF REQUIREMENTS FOR A STRUCTURAL EFFICIENCY INDICATOR OF UNEQUAL-ENERGY COMPLEX SIGNAL ENSEMBLES IN CODE DIVISION MULTIPLE ACCESS SYSTEMS
DOI:
https://doi.org/10.18664/1994-7852.216.2026.362542Ключові слова:
structural efficiency indicator, unequal-energy complex signal ensemble, code division multiple access system, multiple-access interference, cross-correlation, total squared correlationАнотація
The characteristics of a code division multiple access system significantly depend on the choice of an ensemble of complex signals. The structure of the complex signals in the ensemble is taken into account through the cross-correlation of the signals and the signal energies in the ratio of useful signal energy to the total energy of multiple-access interference and noise. For ensembles of equal-energy complex signals, the available efficiency indicators make it possible to estimate the influence of the ensemble on multiple-access interference without separately taking into account the signal energy distribution, since the signals can be normalized to unit energy. For ensembles of unequal-energy complex signals, the signal energy distribution affects the level of multiple-access interference together with the cross-correlation of the signals. The purpose of the article is to substantiate the requirements for the structural efficiency indicator of ensembles of unequal-energy complex signals in code division multiple access systems on the basis of analysis of multiple-access interference energy and the ratio of useful signal energy to the total energy of multiple-access interference and noise. It is established that, for assessing complex signal ensembles, it is appropriate to distinguish between indicators through which the ratio of useful signal energy to the total energy of multiple-access interference and noise can be expressed directly and general squared-correlation functionals that do not provide such a direct expression. For equal-energy ensembles, the assessment of structural efficiency can be reduced to the cross-correlations of the signals, and the structural efficiency indicator can be the product of the signal ensemble size and the square of the maximum ensemble-wide value of cross-correlation. For unequal-energy ensembles, the total energy of multiple-access interference is not reduced to a form analogous to the equal-energy case, because it is simultaneously affected by the cross-correlations of the signals and by the nonuniform distribution of their energies. Taking into account the analysis performed, the following requirements should be imposed on the structural efficiency indicator of unequal-energy complex signal ensembles: the indicator should be related to the signal-to-interference-plus-noise ratio, be sensitive to unfavorable cases of multiple-access interference realization, and be suitable for ranking and comparing unequal-energy complex signal ensembles of different sizes, while remaining consistent with the equal-energy limiting case.
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