@article{EJP727,
author = {Werner Linde and Antoine Ayache},
title = {Series Representations of Fractional Gaussian Processes by Trigonometric and Haar Systems},
journal = {Electron. J. Probab.},
fjournal = {Electronic Journal of Probability},
volume = {14},
year = {2009},
keywords = {Approximation of operators and processes, Rie-mann--Liouville operator, Riemann--Liouville process, Haar system, trigonometric system.},
abstract = {The aim of the present paper is to investigate series representations of the Riemann-Liouville process $R^\alpha$, $\alpha >1/2$, generated by classical orthonormal bases in $L_2[0,1]$. Those bases are, for example, the trigonometric or the Haar system. We prove that the representation of $R^\alpha$ via the trigonometric system possesses the optimal convergence rate if and only if $1/2 < \alpha\leq 2$. For the Haar system we have an optimal approximation rate if $1/2 < \alpha <3/2$ while for $\alpha > 3/2$ a representation via the Haar system is not optimal. Estimates for the rate of convergence of the Haar series are given in the cases $\alpha > 3/2$ and $\alpha = 3/2$. However, in this latter case the question whether or not the series representation is optimal remains open. Recently M. A. Lifshits answered this question (cf. [13]). Using a different approach he could show that in the case $\alpha = 3/2$ a representation of the Riemann-Liouville process via the Haar system is also not optimal.},
pages = {no. 94, 2691-2719},
issn = {1083-6489},
doi = {10.1214/EJP.v14-727},
url = {http://ejp.ejpecp.org/article/view/727}}