  The minimum mean-square error of the estimation of a signal where observed
from the additive white Gaussian noise (WGN) channel's output, is analyzed. It
is assumed that the channel input's signal is composed of a (normalized) sum of
N narrowband, mutually independent waves. It is shown that if N goes to
infinity, then for any fixed signal energy to noise energy ratio (no mater how
big) both the causal minimum mean-square error CMMSE and the non-causal minimum
mean-square error MMSE converge to the signal energy at a rate which is
proportional to 1/N.
