Representation of cascade codes in the frequency domain

The mathematical apparatus of the multidimensional discrete Fourier transform over finite fields is considered. Methods for the description of linear block codes in the frequency domain are investigated. It is shown that, in contrast to iterative codes (code-products), cascade codes in the general case cannot be described in the frequency domain in terms of multidimensional spectra. Analytic expressions are obtained that establish a one-to-one functional correspondence between the spectrum of a sequence over a finite field and the spectra of the corresponding words obtained by limiting this word to a subfield. A general solution of the problem of representation of cascade codes in the frequency domain is obtained, which allows constructing in the frequency domain using computationally efficient algorithms of encoding and decoding, and the derived analytic dependences of components of multidimensional spectra.