  In wireless networks, frequent reference signal transmission for accurate
channel reconstruction may reduce spectral efficiency. To address this issue,
we consider to use a data-carrying reference signal (DC-RS) that can
simultaneously estimate channel coefficients and transmit data symbols. Here,
symbols on the Grassmann manifold are exploited to carry additional data and to
assist in channel estimation. Unlike conventional studies, we analyze the
channel estimation errors induced by DC-RS and propose an optimization method
that improves the channel estimation accuracy without performance penalty.
Then, we derive the achievable rate of noncoherent Grassmann constellation
assuming discrete inputs in multi-antenna scenarios, as well as that of
coherent signaling assuming channel estimation errors modeled by the
Gauss-Markov uncertainty. These derivations enable performance evaluation when
introducing DC-RS, and suggest excellent potential for boosting spectral
efficiency, where interesting crossings with the non-data carrying RS occurred
at intermediate signal-to-noise ratios.
