  We consider a class of spatially flat cold dark matter (CDM) models, with a
cosmological constant and a broken-scale-invariant (BSI) steplike primordial
spectrum of adiabatic perturbations, previously found to be in very good
agreement with observations. Performing a Fisher matrix analysis, we show that
in case of a large gravitational waves (GW) contribution some free parameters
(defining the step) of our BSI model can be extracted with remarkable accuracy
by the Planck satellite, thanks to the polarisation anisotropy measurements.
Further, cosmological parameters can still be found with very good precision,
despite a larger number of free parameters than in the simplest inflationary
models.
