# Self-correlation vs Digital frequency: figure from paper

In the paper, is discussed a MIMO-OFDM system over the frequency self-correlation of i.i.d. Rayleigh channels and subcarrier grouping. in this paper is shown the following figure.

it shows the self-correlations of different fading environments.

Questions:

1. It is shown autocorrelation function in this figure, isnt?
2. What conlusion can I do accroding to this figure?