Definition (Excursion time)
Define the length of the r-th excursion to state i as the difference between passage times or Si(r)=Ti(r)−Ti(r−1)for r≥1.
Lemma (Excursion Time Lemma)
By strong markov property Si(2),Si(3),… are iid. With common distribution is distribution of Si(2) conditional on X0=i
Lemma (Excursion Time Lemma)
Assume X1=i and P recurrent, then:
- Si(2),Si(3),… are iid
- P(limr→∞r1Ti(r)=mi)=1 where mi=Ei[Ti(1)]