  In this paper, for a single-input multiple-output (SIMO) system aided by a
passive reconfigurable intelligent surface (RIS), the joint transmission
accomplished by the single transmit antenna and the RIS with multiple
controllable reflective elements is considered. Relying on a general capacity
upper bound derived by a maximum-trace argument, we respectively characterize
the capacity of such \rev{a} channel in the low-SNR or the rank-one regimes, in
which the optimal configuration of the RIS is proved to be beamforming with
carefully-chosen phase shifts. To exploit the potential of modulating extra
information on the RIS, based on the QR decomposition, successive interference
cancellation, and a strategy named \textit{partially beamforming and partially
information-carrying}, we propose a novel transceiver architecture with only a
single RF front end at the transmitter, by which the considered channel can be
regarded as a concatenation of a vector Gaussian channel and several
phase-modulated channels. Especially, we investigate a class of vector Gaussian
channels with a hypersphere input support constraint, and not only generalize
the existing result to arbitrary-dimensional real spaces but also present its
high-order capacity asymptotics, by which both capacities of
hypersphere-constrained channels and achievable rates of the proposed
transceiver with two different signaling schemes can be well-approximated.
Information-theoretic analyses show that the transceiver architecture designed
for the SIMO channel has a boosted multiplexing gain, rather than one for the
conventionally-used optimized beamforming scheme.Numerical results verify our
derived asymptotics and show notable superiority of the proposed transceiver.
