The classical theory of Fourier series deals with decomposition of a function into sinusoidal waves. Unlike these continuous waves the Vilenkin (Walsh) functions are rectangular waves. Such waves have already been used frequently in the theory of signal transmission, multiplexing, filtering, image enhancement, code theory, digital signal processing and pattern recognition. The development of the theory of Vilenkin-Fourier series has been strongly influenced by the classical theory of trigonometric series. Because of this it is inevitable to compare results of Vilenkin-Fourier series to those on trigonometric series. There are many similarities between these theories, but there exist differences also. Much of these can be explained by modern abstract harmonic analysis, which studies orthonormal systems from the point of view of the structure of a topological group.
The first part of the book can be used as an introduction to the subject, and the following chapters summarize the most recent research in this fascinating area and can be read independently. Each chapter concludes with historical remarks and open questions. The book will appeal to researchers working in Fourier and more broad harmonic analysis and will inspire them for their own and their students' research. Moreover, researchers in applied fields will appreciate it as a sourcebook far beyond the traditional mathematical domains.

Involves several applications (signal transmission, multiplexing, filtering, image enhancement, code theory) Develops the theory of Vilenkin-Fourier series in the harmonic analysis context Connects classic theories to modern harmonic analysis

Résumé
"The book offers a wonderful overview, very well structured and complete, on the theory of harmonic analysis developed in the context of the Vilenkin-Fourier series. ... each chapter begins with a broad introduction rich in bibliographical citations that allow the reader to locate himself in the historical context of the topics to be addressed ... the authors include an important and interesting list of open problems proposed with a view to being resolved in future research." (Iris Athamaica López Palacios, zbMATH 1512.42042, 2023)

Contenu

1. Partial Sums of Vilenkin-Fourier Series in Lebesgue Spaces. - 2. Martingales and Almost Everywhere Convergence of Partial Sums of Vilenkin-Fourier Series. - 3. Vilenkin-Fejér Means and an Approximate Identityin Lebesgue Spaces. - 4. Nörlund and T Means of Vilenkin-Fourier Series in Lebesgue Spaces. - 5. Theory of Martingale Hardy Spaces. - 6. Vilenkin-Fourier Coefficients and Partial Sums in Martingale Hardy Spaces. - 7. Vilenkin-Fejér Means in Martingale Hardy Spaces. - 8. Nörlund and T Means of Vilenkin-Fourier Series in Martingale Hardy Spaces. - 9. Convergence of Vilenkin-Fourier Series in Variable Martingale Hardy Spaces. - 10. Appendix: Dyadic Group and Walsh and Kaczmarz Systems.