  We present a comprehensive analysis for the determination of the confusion
levels for the current and the next generation of far-infrared surveys assuming
three different cosmological evolutionary scenarios. We include an extensive
model for diffuse emission from infrared cirrus in order to derive absolute
sensitivity levels taking into account the source confusion noise due to point
sources, the sky confusion noise due to the diffuse emission, and instrumental
noise. We use our derived sensitivities to suggest best survey strategies for
the current and the future far-infrared space missions Spitzer, AKARI
(ASTRO-F), Herschel, and SPICA. We discuss whether the theoretical estimates
are realistic and the competing necessities of reliability and completeness. We
find the best estimator for the representation of the source confusion and
produce predictions for the source confusion using far-infrared source count
models. From these confusion limits considering both source and sky confusions,
we obtain the optimal, confusion limited redshift distribution for each
mission. Finally, we predict the Cosmic Far-Infrared Background (CFIRB) which
includes information about the number and distribution of the contributing
sources.
