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In radar systems, when solving the problem of detecting objects behind dielectrically transparent obstacles against a background of noise and interference, methods of compressing modulated UWB signals are often used. The most widespread in solving this problem are Barker codes, which are binary sequences of finite length N = 2,3,4,5,7,11,13. One of the main features of Barker codes is the equality of the amplitudes of all lateral maxima of the autocorrelation function at their minimum possible level not exceeding 1 / N. Code sequences with such properties have not been found for N< 13. Recently, the theory of quasi-orthogonal matrices has arisen and is being developed, which include the Mersenne and Raghavararo matrices. Mersenne matrices exist in all orders N = 4n-1, where n is a natural number. The indicated matrices, which are the kernel of the Hadamard matrices and generalize them, can have both cyclic and symmetric constructions. In this paper, we consider the modulation of UWB signals using the Mersenne and Raghavararo codes obtained from the rows of the corresponding quasi-orthogonal matrices. The compression characteristics of code-modulated signals in comparison with Barker codes are investigated by the method of simulation modeling. The results of evaluating the compression characteristics of the considered signals showed the advisability of using, for example, for N = 13 the Raghavararo code instead of the Barker codes. This provides greater noise immunity of UWB signals in the channels for detecting objects behind obstacles. Since, in addition to radar systems, the Barker sequence of length 11 is widely used in digital data transmission systems, the developed simulation model and the results obtained using Mersenne codes are of great theoretical and practical importance in studies of noise immunity in digital UWB data transmission channels in a complex electromagnetic environment.
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