In matlab I modelled. I have received results about what you spoke. Abou
dispersive the communications channel it is clear. And about shape th
frequency spectrum of the subcarriers - I see that dependence is, but
can not mathematicly describe it.

For example, at me is 12 subcarriers, on everyone subcarrier - PSK4
everyone has speed of transfer of 50 bod.

What length of a prefix should be if the interval between subcarriers i
100Hz?.
And what length of a prefix should be if the interval between subcarrier
is 60Hz?
How it can be mathematicly calculated?