On the uniform ergodicity of Markov processes of order 2

Abstract

We study the uniform ergodicity of Markov processes (Z_n, n ≥ 1) of order 2 with a general state space (Z, Z). Markov processes of order higher than 1 were defined in the literature long ago, but scarcely treated in detail. We take as the basis for our considerations the natural transition probability Q of such a process. A Markov process of order 2 is transformed into one of order 1 by combining two consecutive variables Z_2n-1 and Z_2n into one variable Y_n with values in the Cartesian product space (Z x Z, Z ⊗ Z). Thus, a Markov process (Y_n, n ≥ 1) of order 1 with transition probability R is generated. Uniform ergodicity for the process (Z_n, n ≥ 1) is defined in terms of the same property for (Y_n, n ≥ 1). We give some conditions on the transition probability Q which transfer to R and thus ensure the uniform ergodicity of (Z_n, n ≥ 1). We apply the general results to study the uniform ergodicity of Markov processes of order 2 which arise in some nonlinear time series models and as sequences of smoothed values in sequential smoothing procedures of Markovian observations. As for the time series models, Markovian noise sequences are covered.