  We consider non-orthogonal multiple access (NOMA) downlink with a
multiple-antenna base station (BS) and single-antenna mobile users. Cell-edge
users that are blocked from the BS are assisted by intelligent reflective
surface (IRS) for data reception. Cell-center and IRS-assist users are paired
to share the same frequency-time resource block and zeroforcing transmit
beamforming from the BS. We propose to optimize IRS-element coefficients and
transmit power to minimize the total power for a given rate threshold.
Differing from the existing work, the proposed joint optimization is based on
channel covariance instead of fast-changing channel coefficients. Our scheme
can reduce larger total power when the number of IRS elements increases. The
performance of IRS-assist users decreases significantly if the rank of BS-IRS
channel matrix is low.
