Wednesday, 13 February 2008

pr.probability - Problem with a Long Range Correlated Time Series

Consider a stochastic process Xt , tin1,2,3,..,N.



Xt is a Bernoulli variable and Pr(Xt=1)=p for all t.
The Autocovariance function gamma(|st|)=E[(Xtp)(Xsp)] is given



gamma(k)=frac12(|k1|2H2|k|2H+|k+1|2H).



For a constant Hin(0,1) This is the same autocovariance as for fractional gaussian noise (increments of the fractional brownian motion), and give a autocovariance which falls like a power law when k goes to infinity.



Let X and Y be process with the given properties, I am interested in the following probability distribution:



Prleft(sumNi=0XiYi=kright)



That is the distribution of the overlap of two such processes. For H=1/2 the process is not correlated and I have the simple result that Pr(XtYt)=p2, and that



Prleft(sumNi=0XiYi=kright)=Nchoosekp2k(1p2)Nk.



But for Hneq1/2, I do not know how to deal with the long range correlation. Is there a way to proceed on this problem? I regret i never took a class in Stochastic Analysis, and I really hope the question makes sense. Any help or input would be highly appreciated.

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