You may need some portion of the Time Series Analysis. Read about two topics "Stationary Processes" and "Spectral Analysis". I guess this will be enough to cover part in the article.
Wiki links are:
http://en.wikipedia.org/wiki/Stationary_process & http://en.wikipedia.org/wiki/Spectral_theory
The Two topics covered in Chpter 2 and Chapter 4 in Brockwell Davis's book "Introduction to Time Series and Forecasting"