  To support massive connectivity and boost spectral efficiency for internet of
things (IoT), a downlink scheme combining virtual multiple-input
multiple-output (MIMO) and nonorthogonal multiple access (NOMA) is proposed.
All the single-antenna IoT devices in each cluster cooperate with each other to
establish a virtual MIMO entity, and multiple independent data streams are
requested by each cluster. NOMA is employed to superimpose all the requested
data streams, and each cluster leverages zero-forcing detection to de-multiplex
the input data streams. Only statistical channel state information (CSI) is
available at base station to avoid the waste of the energy and bandwidth on
frequent CSI estimations. The outage probability and goodput of the virtual
MIMO-NOMA system are thoroughly investigated by considering Kronecker model,
which embraces both the transmit and receive correlations. Furthermore, the
asymptotic results facilitate not only the exploration of physical insights but
also the goodput maximization. In particular, the asymptotic outage expressions
provide quantitative impacts of various system parameters and enable the
investigation of diversity-multiplexing tradeoff (DMT). Moreover, power
allocation coefficients and/or transmission rates can be properly chosen to
achieve the maximal goodput. By favor of Karush-Kuhn-Tucker conditions, the
goodput maximization problems can be solved in closed-form, with which the
joint power and rate selection is realized by using alternately iterating
optimization.Besides, the optimization algorithms tend to allocate more power
to clusters under unfavorable channel conditions and support clusters with
higher transmission rate under benign channel conditions.
