  The spectral efficiency achievable with joint processing of pilot and data
symbol observations is compared with that achievable through the conventional
(separate) approach of first estimating the channel on the basis of the pilot
symbols alone, and subsequently detecting the data symbols. Studied on the
basis of a mutual information lower bound, joint processing is found to provide
a non-negligible advantage relative to separate processing, particularly for
fast fading. It is shown that, regardless of the fading rate, only a very small
number of pilot symbols (at most one per transmit antenna and per channel
coherence interval) should be transmitted if joint processing is allowed.
