Is there just a carrier in each frequency band in FDMA? The figure is the FDMA,and i know that FDMA is that dividing the bandwidth into many blocks(frequency band),i want to ask Is there just a carrier in each frequency band in  FDMA?i mean one carrier for User1 ,one carrier for User2,and one carrier for User3,and so on.Or for the user N,there are lots of carrier in it,if i want to send a signal,then i have to use a carrier?
That's undefined.

FDMA just says that different users use different parts of the spectrum.

What these users do within "their" frequency ranges is up to the system to define.