Joint temporal and contemporaneous aggregation of random-coefficient AR(1) processes

Abstract

We discuss joint temporal and contemporaneous aggregation of $N$ independent copies of AR(1) process with random-coefficient $a \in [0,1)$ when $N$ and time scale $n$ increase at different rate. Assuming that $a$ has a density, regularly varying at $a = 1$ with exponent $-1 < \beta < 1$, different joint limits of normalized aggregated partial sums are shown to exist when $N^{1/(1+\beta)}/n$ tends to (i) $\infty$, (ii) 0, (iii) $0 < \mu < \infty$. The limit process arising under (iii) admits a Poisson integral representation on $(0,\infty) \times C(\mathbb{R})$ and enjoys "intermediate" properties between fractional Brownian motion limit in (i) and sub-Gaussian limit in (ii).